[PATCH 0/1] btrfs: Tree lock return value enhancement to avoid deadlock on crafted image

[PATCH 0/1] btrfs: Tree lock return value enhancement to avoid deadlock on crafted image

[Qu Wenruo]

The patch along with all submitted patches for fuzzed image can be found
at the following repo:
https://github.com/adam900710/linux/tree/tree_checker_enhance

Although fuzzed images are not really possible to happen in real world,
it's still a pretty possible Deny of Service to attack the kernel, so we
still need to address such problems.

Instead of previous failed attempt to use cached eb to determine if
we're allocating new tree blocks on already used tree block, this time
we allow btrfs_tree_lock() to return error number to inform callers
there is something wrong so we can exit a little more gracefully.

This branch should address the 2nd wave of fuzzed images reported by Xu
Wen.

Please note, since extent tree corruption is the worst scenario, we
still keep kernel to WARN() on such problem.
But at least for that fuzzed image we can switched to RO other than
deadlock the kernel.

Qu Wenruo (1):
  btrfs: locking: Allow btrfs_tree_lock() to return error to avoid
    deadlock

 fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
 fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
 fs/btrfs/extent_io.c       |  8 ++++--
 fs/btrfs/free-space-tree.c |  4 ++-
 fs/btrfs/locking.c         | 12 ++++++--
 fs/btrfs/locking.h         |  2 +-
 fs/btrfs/qgroup.c          |  4 ++-
 fs/btrfs/relocation.c      | 13 +++++++--
 fs/btrfs/tree-log.c        | 14 ++++++++--
 9 files changed, 114 insertions(+), 28 deletions(-)

-- 
2.18.0

[PATCH 1/1] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

[BUG]
For certains crafted image, whose csum root leaf has missing backref, if
we try to trigger write with data csum, it could cause deadlock with the
following kernel WARN_ON():
------
WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230 btrfs_tree_lock+0x3e2/0x400
CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
Workqueue: btrfs-endio-write btrfs_endio_write_helper
RIP: 0010:btrfs_tree_lock+0x3e2/0x400
Call Trace:
 btrfs_alloc_tree_block+0x39f/0x770
 __btrfs_cow_block+0x285/0x9e0
 btrfs_cow_block+0x191/0x2e0
 btrfs_search_slot+0x492/0x1160
 btrfs_lookup_csum+0xec/0x280
 btrfs_csum_file_blocks+0x2be/0xa60
 add_pending_csums+0xaf/0xf0
 btrfs_finish_ordered_io+0x74b/0xc90
 finish_ordered_fn+0x15/0x20
 normal_work_helper+0xf6/0x500
 btrfs_endio_write_helper+0x12/0x20
 process_one_work+0x302/0x770
 worker_thread+0x81/0x6d0
 kthread+0x180/0x1d0
 ret_from_fork+0x35/0x40
---[ end trace 2e85051acb5f6dc1 ]---
------

[CAUSE]
That crafted image has missing backref for csum tree root leaf.
And when we try to allocate new tree block, since there is no
EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
and use it.

However we have already locked csum tree root leaf by ourselves, thus we
will ourselves to release read/write lock, and causing deadlock.

[FIX]
This patch will allow btrfs_tree_lock() to return error number, so
most callers can exit gracefully.
(Some caller doesn't really expect btrfs_tree_lock() to return error,
and in that case, we use BUG_ON())

Since such problem can only happen in crafted image, we will still
trigger kernel warning, but with a little more meaningful warning
message.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
Reported-by: Xu Wen <wen.xu@gatech.edu>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
 fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
 fs/btrfs/extent_io.c       |  8 ++++--
 fs/btrfs/free-space-tree.c |  4 ++-
 fs/btrfs/locking.c         | 12 ++++++--
 fs/btrfs/locking.h         |  2 +-
 fs/btrfs/qgroup.c          |  4 ++-
 fs/btrfs/relocation.c      | 13 +++++++--
 fs/btrfs/tree-log.c        | 14 ++++++++--
 9 files changed, 114 insertions(+), 28 deletions(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 4bc326df472e..6e695f4cd931 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -161,10 +161,12 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
 {
 	struct extent_buffer *eb;
+	int ret;
 
 	while (1) {
 		eb = btrfs_root_node(root);
-		btrfs_tree_lock(eb);
+		ret = btrfs_tree_lock(eb);
+		BUG_ON(ret < 0);
 		if (eb == root->node)
 			break;
 		btrfs_tree_unlock(eb);
@@ -1584,6 +1586,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 	for (i = start_slot; i <= end_slot; i++) {
 		struct btrfs_key first_key;
 		int close = 1;
+		int ret;
 
 		btrfs_node_key(parent, &disk_key, i);
 		if (!progress_passed && comp_keys(&disk_key, progress) < 0)
@@ -1637,7 +1640,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 		if (search_start == 0)
 			search_start = last_block;
 
-		btrfs_tree_lock(cur);
+		ret = btrfs_tree_lock(cur);
+		if (ret < 0) {
+			free_extent_buffer(cur);
+			return ret;
+		}
 		btrfs_set_lock_blocking(cur);
 		err = __btrfs_cow_block(trans, root, cur, parent, i,
 					&cur, search_start,
@@ -1853,7 +1860,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 			goto enospc;
 		}
 
-		btrfs_tree_lock(child);
+		ret = btrfs_tree_lock(child);
+		if (ret < 0) {
+			free_extent_buffer(child);
+			goto enospc;
+		}
 		btrfs_set_lock_blocking(child);
 		ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
 		if (ret) {
@@ -1891,7 +1902,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		left = NULL;
 
 	if (left) {
-		btrfs_tree_lock(left);
+		ret = btrfs_tree_lock(left);
+		if (ret < 0) {
+			free_extent_buffer(left);
+			left = NULL;
+			goto enospc;
+		}
 		btrfs_set_lock_blocking(left);
 		wret = btrfs_cow_block(trans, root, left,
 				       parent, pslot - 1, &left);
@@ -1906,7 +1922,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		right = NULL;
 
 	if (right) {
-		btrfs_tree_lock(right);
+		ret = btrfs_tree_lock(right);
+		if (ret < 0) {
+			free_extent_buffer(right);
+			right = NULL;
+			goto enospc;
+		}
 		btrfs_set_lock_blocking(right);
 		wret = btrfs_cow_block(trans, root, right,
 				       parent, pslot + 1, &right);
@@ -2069,7 +2090,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 	if (left) {
 		u32 left_nr;
 
-		btrfs_tree_lock(left);
+		ret = btrfs_tree_lock(left);
+		if (ret < 0) {
+			free_extent_buffer(left);
+			return ret;
+		}
 		btrfs_set_lock_blocking(left);
 
 		left_nr = btrfs_header_nritems(left);
@@ -2124,7 +2149,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 	if (right) {
 		u32 right_nr;
 
-		btrfs_tree_lock(right);
+		ret = btrfs_tree_lock(right);
+		if (ret < 0) {
+			free_extent_buffer(right);
+			return ret;
+		}
 		btrfs_set_lock_blocking(right);
 
 		right_nr = btrfs_header_nritems(right);
@@ -2874,7 +2903,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 					err = btrfs_try_tree_write_lock(b);
 					if (!err) {
 						btrfs_set_path_blocking(p);
-						btrfs_tree_lock(b);
+						ret = btrfs_tree_lock(b);
+						if (ret < 0)
+							goto done;
 						btrfs_clear_path_blocking(p, b,
 								  BTRFS_WRITE_LOCK);
 					}
@@ -3773,7 +3804,9 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 	if (IS_ERR(right))
 		return 1;
 
-	btrfs_tree_lock(right);
+	ret = btrfs_tree_lock(right);
+	if (ret < 0)
+		goto out_free;
 	btrfs_set_lock_blocking(right);
 
 	free_space = btrfs_leaf_free_space(fs_info, right);
@@ -3811,6 +3844,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 				right, free_space, left_nritems, min_slot);
 out_unlock:
 	btrfs_tree_unlock(right);
+out_free:
 	free_extent_buffer(right);
 	return 1;
 }
@@ -4007,7 +4041,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 	if (IS_ERR(left))
 		return 1;
 
-	btrfs_tree_lock(left);
+	ret = btrfs_tree_lock(left);
+	if (ret < 0)
+		goto out_free;
 	btrfs_set_lock_blocking(left);
 
 	free_space = btrfs_leaf_free_space(fs_info, left);
@@ -4037,6 +4073,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 			       max_slot);
 out:
 	btrfs_tree_unlock(left);
+out_free:
 	free_extent_buffer(left);
 	return ret;
 }
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3578fa5b30ef..da615ebc072e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8297,14 +8297,19 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct extent_buffer *buf;
+	int ret;
 
 	buf = btrfs_find_create_tree_block(fs_info, bytenr);
 	if (IS_ERR(buf))
 		return buf;
+	ret = btrfs_tree_lock(buf);
+	if (ret < 0) {
+		free_extent_buffer(buf);
+		return ERR_PTR(ret);
+	}
 
 	btrfs_set_header_generation(buf, trans->transid);
 	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
-	btrfs_tree_lock(buf);
 	clean_tree_block(fs_info, buf);
 	clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
 
@@ -8721,7 +8726,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 					       level - 1);
 		reada = 1;
 	}
-	btrfs_tree_lock(next);
+	ret = btrfs_tree_lock(next);
+	if (ret < 0)
+		goto out_free;
 	btrfs_set_lock_blocking(next);
 
 	ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
@@ -8781,7 +8788,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 			free_extent_buffer(next);
 			return -EIO;
 		}
-		btrfs_tree_lock(next);
+		ret = btrfs_tree_lock(next);
+		if (ret < 0)
+			goto out_free;
 		btrfs_set_lock_blocking(next);
 	}
 
@@ -8839,6 +8848,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 
 out_unlock:
 	btrfs_tree_unlock(next);
+out_free:
 	free_extent_buffer(next);
 
 	return ret;
@@ -8887,7 +8897,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 		 */
 		if (!path->locks[level]) {
 			BUG_ON(level == 0);
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			BUG_ON(ret < 0);
 			btrfs_set_lock_blocking(eb);
 			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 
@@ -8929,7 +8940,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 		/* make block locked assertion in clean_tree_block happy */
 		if (!path->locks[level] &&
 		    btrfs_header_generation(eb) == trans->transid) {
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			BUG_ON(ret < 0);
 			btrfs_set_lock_blocking(eb);
 			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 		}
@@ -9107,7 +9119,11 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
 
 		level = btrfs_header_level(root->node);
 		while (1) {
-			btrfs_tree_lock(path->nodes[level]);
+			ret = btrfs_tree_lock(path->nodes[level]);
+			if (ret < 0) {
+				err = ret;
+				goto out_end_trans;
+			}
 			btrfs_set_lock_blocking(path->nodes[level]);
 			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index cce6087d6880..3ba02aac6dd5 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3545,7 +3545,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
 	if (!btrfs_try_tree_write_lock(eb)) {
 		flush = 1;
 		flush_write_bio(epd);
-		btrfs_tree_lock(eb);
+		ret = btrfs_tree_lock(eb);
+		if (ret < 0)
+			return ret;
 	}
 
 	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
@@ -3558,7 +3560,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
 		}
 		while (1) {
 			wait_on_extent_buffer_writeback(eb);
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			if (ret < 0)
+				return ret;
 			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
 				break;
 			btrfs_tree_unlock(eb);
diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index b5950aacd697..948bbc45638a 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -1242,7 +1242,9 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
 
 	list_del(&free_space_root->dirty_list);
 
-	btrfs_tree_lock(free_space_root->node);
+	ret = btrfs_tree_lock(free_space_root->node);
+	if (ret < 0)
+		goto abort;
 	clean_tree_block(fs_info, free_space_root->node);
 	btrfs_tree_unlock(free_space_root->node);
 	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 1da768e5ef75..aa4a3362a9f1 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -224,10 +224,18 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
 /*
  * take a spinning write lock.  This will wait for both
  * blocking readers or writers
+ *
+ * Return 0 if we successfully locked the tree block
+ * Return <0 if some selftest failed (mostly due to extent tree corruption)
  */
-void btrfs_tree_lock(struct extent_buffer *eb)
+int btrfs_tree_lock(struct extent_buffer *eb)
 {
-	WARN_ON(eb->lock_owner == current->pid);
+	if (unlikely(eb->lock_owner == current->pid)) {
+		WARN(1,
+"tree block %llu already locked by current (pid=%llu), refuse to lock",
+		     eb->start, current->pid);
+		return -EUCLEAN;
+	}
 again:
 	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
 	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
index 29135def468e..7394d7ba2ff9 100644
--- a/fs/btrfs/locking.h
+++ b/fs/btrfs/locking.h
@@ -11,7 +11,7 @@
 #define BTRFS_WRITE_LOCK_BLOCKING 3
 #define BTRFS_READ_LOCK_BLOCKING 4
 
-void btrfs_tree_lock(struct extent_buffer *eb);
+int btrfs_tree_lock(struct extent_buffer *eb);
 void btrfs_tree_unlock(struct extent_buffer *eb);
 
 void btrfs_tree_read_lock(struct extent_buffer *eb);
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 1874a6d2e6f5..ec4351fd7537 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
 
 	list_del(&quota_root->dirty_list);
 
-	btrfs_tree_lock(quota_root->node);
+	ret = btrfs_tree_lock(quota_root->node);
+	if (ret < 0)
+		goto out;
 	clean_tree_block(fs_info, quota_root->node);
 	btrfs_tree_unlock(quota_root->node);
 	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index be94c65bb4d2..a2fc0bd83a40 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
 				free_extent_buffer(eb);
 				break;
 			}
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			if (ret < 0) {
+				free_extent_buffer(eb);
+				break;
+			}
 			if (cow) {
 				ret = btrfs_cow_block(trans, dest, eb, parent,
 						      slot, &eb);
@@ -2788,7 +2792,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
 			err = -EIO;
 			goto next;
 		}
-		btrfs_tree_lock(eb);
+		ret = btrfs_tree_lock(eb);
+		if (ret < 0) {
+			free_extent_buffer(eb);
+			err = ret;
+			goto next;
+		}
 		btrfs_set_lock_blocking(eb);
 
 		if (!node->eb) {
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index f8220ec02036..173bc15a7cd1 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
 				}
 
 				if (trans) {
-					btrfs_tree_lock(next);
+					ret = btrfs_tree_lock(next);
+					if (ret < 0) {
+						free_extent_buffer(next);
+						return ret;
+					}
 					btrfs_set_lock_blocking(next);
 					clean_tree_block(fs_info, next);
 					btrfs_wait_tree_block_writeback(next);
@@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
 				next = path->nodes[*level];
 
 				if (trans) {
-					btrfs_tree_lock(next);
+					ret = btrfs_tree_lock(next);
+					if (ret < 0)
+						return ret;
 					btrfs_set_lock_blocking(next);
 					clean_tree_block(fs_info, next);
 					btrfs_wait_tree_block_writeback(next);
@@ -2754,7 +2760,9 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
 			next = path->nodes[orig_level];
 
 			if (trans) {
-				btrfs_tree_lock(next);
+				ret = btrfs_tree_lock(next);
+				if (ret < 0)
+					goto out;
 				btrfs_set_lock_blocking(next);
 				clean_tree_block(fs_info, next);
 				btrfs_wait_tree_block_writeback(next);
-- 
2.18.0

Re: [PATCH 1/1] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Nikolay Borisov]

On 30.07.2018 09:17, Qu Wenruo wrote:
> -void btrfs_tree_lock(struct extent_buffer *eb)
> +int btrfs_tree_lock(struct extent_buffer *eb)
>  {
> -	WARN_ON(eb->lock_owner == current->pid);
> +	if (unlikely(eb->lock_owner == current->pid)) {
> +		WARN(1,
> +"tree block %llu already locked by current (pid=%llu), refuse to lock",
> +		     eb->start, current->pid);
> +		return -EUCLEAN;
> +	}

If this happens it should point to a logical bug in which case we need
to halt the kernel. Furthermore this seems the wrong abstraction level
at which to solve the problem. eb->lock_owner is a runtime
characteristic of the eb, yet when it has an unexpected value you return
EUCLEAN which is an error for an on-disk error.

I don't think it's productive to try and solve every possible
fuzz-inspired corruption. In the worst case this corruption should be
caught a lot earlier rather than when we are locking an in-memory
structure.

Re: [PATCH 1/1] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

On 2018年07月30日 15:18, Nikolay Borisov wrote:
> 
> 
> On 30.07.2018 09:17, Qu Wenruo wrote:
>> -void btrfs_tree_lock(struct extent_buffer *eb)
>> +int btrfs_tree_lock(struct extent_buffer *eb)
>>  {
>> -	WARN_ON(eb->lock_owner == current->pid);
>> +	if (unlikely(eb->lock_owner == current->pid)) {
>> +		WARN(1,
>> +"tree block %llu already locked by current (pid=%llu), refuse to lock",
>> +		     eb->start, current->pid);
>> +		return -EUCLEAN;
>> +	}
> 
> If this happens it should point to a logical bug in which case we need
> to halt the kernel. Furthermore this seems the wrong abstraction level
> at which to solve the problem. eb->lock_owner is a runtime
> characteristic of the eb, yet when it has an unexpected value you return
> EUCLEAN which is an error for an on-disk error.

On-disk corruption leads to unexpected runtime error, this looks valid
to me at least.
Especially when we can't really verify on-disk data for it's cross
reference.

> 
> I don't think it's productive to try and solve every possible
> fuzz-inspired corruption.

Surprisingly, we should.

The point here is, such image can be used to do kernel deny-of-service
attack.
(Such debate happened a long time ago, and at that time I was thinking
the same as you)

No one likes a USB stick to cause kernel deadlock, even for desktop users.

> In the worst case this corruption should be
> caught a lot earlier rather than when we are locking an in-memory
> structure.

This makes sense, although not that doable.
For early detection, we need to do some level cross check, which could
be time and IO consuming.

Currently this fix is the least performance-impacting one I could think of.

Thanks,
Qu

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> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
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> 

Re: [PATCH 1/1] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

On 2018年07月31日 14:48, Su Yue wrote:
> 
> 
> On 07/30/2018 02:17 PM, Qu Wenruo wrote:
>> [BUG]
>> For certains crafted image, whose csum root leaf has missing backref, if
>> we try to trigger write with data csum, it could cause deadlock with the
>> following kernel WARN_ON():
>> ------
>> WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230
>> btrfs_tree_lock+0x3e2/0x400
>> CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
>> Workqueue: btrfs-endio-write btrfs_endio_write_helper
>> RIP: 0010:btrfs_tree_lock+0x3e2/0x400
>> Call Trace:
>>   btrfs_alloc_tree_block+0x39f/0x770
>>   __btrfs_cow_block+0x285/0x9e0
>>   btrfs_cow_block+0x191/0x2e0
>>   btrfs_search_slot+0x492/0x1160
>>   btrfs_lookup_csum+0xec/0x280
>>   btrfs_csum_file_blocks+0x2be/0xa60
>>   add_pending_csums+0xaf/0xf0
>>   btrfs_finish_ordered_io+0x74b/0xc90
>>   finish_ordered_fn+0x15/0x20
>>   normal_work_helper+0xf6/0x500
>>   btrfs_endio_write_helper+0x12/0x20
>>   process_one_work+0x302/0x770
>>   worker_thread+0x81/0x6d0
>>   kthread+0x180/0x1d0
>>   ret_from_fork+0x35/0x40
>> ---[ end trace 2e85051acb5f6dc1 ]---
>> ------
>>
>> [CAUSE]
>> That crafted image has missing backref for csum tree root leaf.
>> And when we try to allocate new tree block, since there is no
>> EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
>> and use it.
>>
>> However we have already locked csum tree root leaf by ourselves, thus we
>> will ourselves to release read/write lock, and causing deadlock.
>>
>> [FIX]
>> This patch will allow btrfs_tree_lock() to return error number, so
>> most callers can exit gracefully.
>> (Some caller doesn't really expect btrfs_tree_lock() to return error,
>> and in that case, we use BUG_ON())
>>
>> Since such problem can only happen in crafted image, we will still
>> trigger kernel warning, but with a little more meaningful warning
>> message.
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
>> Reported-by: Xu Wen <wen.xu@gatech.edu>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
> 
> OK.. I looked through every places where the callee is called.
> Those errors are handled gracefully as my thought.
> Except one nitpick, the %llu about pid_t in btrfs_tree_lock.
> However, you can add the tag:
> 
> Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>

snip

> 
> Nit:
> pid_t is as an signed integer, should be pid=%d .

BTW, how could pid be negative?
And why my gcc doesn't give such warning?

Thanks,
Qu

> 
> Thanks,
> Su
> 
>> +             eb->start, current->pid);
>> +        return -EUCLEAN;
>> +    }
>>   again:
>>       wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers)
>> == 0);
>>       wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers)
>> == 0);
>> diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
>> index 29135def468e..7394d7ba2ff9 100644
>> --- a/fs/btrfs/locking.h
>> +++ b/fs/btrfs/locking.h
>> @@ -11,7 +11,7 @@
>>   #define BTRFS_WRITE_LOCK_BLOCKING 3
>>   #define BTRFS_READ_LOCK_BLOCKING 4
>>   -void btrfs_tree_lock(struct extent_buffer *eb);
>> +int btrfs_tree_lock(struct extent_buffer *eb);
>>   void btrfs_tree_unlock(struct extent_buffer *eb);
>>     void btrfs_tree_read_lock(struct extent_buffer *eb);
>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>> index 1874a6d2e6f5..ec4351fd7537 100644
>> --- a/fs/btrfs/qgroup.c
>> +++ b/fs/btrfs/qgroup.c
>> @@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct
>> btrfs_trans_handle *trans,
>>         list_del(&quota_root->dirty_list);
>>   -    btrfs_tree_lock(quota_root->node);
>> +    ret = btrfs_tree_lock(quota_root->node);
>> +    if (ret < 0)
>> +        goto out;
>>       clean_tree_block(fs_info, quota_root->node);
>>       btrfs_tree_unlock(quota_root->node);
>>       btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
>> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
>> index be94c65bb4d2..a2fc0bd83a40 100644
>> --- a/fs/btrfs/relocation.c
>> +++ b/fs/btrfs/relocation.c
>> @@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
>>                   free_extent_buffer(eb);
>>                   break;
>>               }
>> -            btrfs_tree_lock(eb);
>> +            ret = btrfs_tree_lock(eb);
>> +            if (ret < 0) {
>> +                free_extent_buffer(eb);
>> +                break;
>> +            }
>>               if (cow) {
>>                   ret = btrfs_cow_block(trans, dest, eb, parent,
>>                                 slot, &eb);
>> @@ -2788,7 +2792,12 @@ static int do_relocation(struct
>> btrfs_trans_handle *trans,
>>               err = -EIO;
>>               goto next;
>>           }
>> -        btrfs_tree_lock(eb);
>> +        ret = btrfs_tree_lock(eb);
>> +        if (ret < 0) {
>> +            free_extent_buffer(eb);
>> +            err = ret;
>> +            goto next;
>> +        }
>>           btrfs_set_lock_blocking(eb);
>>             if (!node->eb) {
>> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
>> index f8220ec02036..173bc15a7cd1 100644
>> --- a/fs/btrfs/tree-log.c
>> +++ b/fs/btrfs/tree-log.c
>> @@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct
>> btrfs_trans_handle *trans,
>>                   }
>>                     if (trans) {
>> -                    btrfs_tree_lock(next);
>> +                    ret = btrfs_tree_lock(next);
>> +                    if (ret < 0) {
>> +                        free_extent_buffer(next);
>> +                        return ret;
>> +                    }
>>                       btrfs_set_lock_blocking(next);
>>                       clean_tree_block(fs_info, next);
>>                       btrfs_wait_tree_block_writeback(next);
>> @@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct
>> btrfs_trans_handle *trans,
>>                   next = path->nodes[*level];
>>                     if (trans) {
>> -                    btrfs_tree_lock(next);
>> +                    ret = btrfs_tree_lock(next);
>> +                    if (ret < 0)
>> +                        return ret;
>>                       btrfs_set_lock_blocking(next);
>>                       clean_tree_block(fs_info, next);
>>                       btrfs_wait_tree_block_writeback(next);
>> @@ -2754,7 +2760,9 @@ static int walk_log_tree(struct
>> btrfs_trans_handle *trans,
>>               next = path->nodes[orig_level];
>>                 if (trans) {
>> -                btrfs_tree_lock(next);
>> +                ret = btrfs_tree_lock(next);
>> +                if (ret < 0)
>> +                    goto out;
>>                   btrfs_set_lock_blocking(next);
>>                   clean_tree_block(fs_info, next);
>>                   btrfs_wait_tree_block_writeback(next);
>>
> 
> 
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> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
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Re: [PATCH 1/1] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

On 2018年07月31日 14:44, Qu Wenruo wrote:
> 
> 
> On 2018年07月31日 14:48, Su Yue wrote:
>>
>>
>> On 07/30/2018 02:17 PM, Qu Wenruo wrote:
>>> [BUG]
>>> For certains crafted image, whose csum root leaf has missing backref, if
>>> we try to trigger write with data csum, it could cause deadlock with the
>>> following kernel WARN_ON():
>>> ------
>>> WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230
>>> btrfs_tree_lock+0x3e2/0x400
>>> CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
>>> Workqueue: btrfs-endio-write btrfs_endio_write_helper
>>> RIP: 0010:btrfs_tree_lock+0x3e2/0x400
>>> Call Trace:
>>>   btrfs_alloc_tree_block+0x39f/0x770
>>>   __btrfs_cow_block+0x285/0x9e0
>>>   btrfs_cow_block+0x191/0x2e0
>>>   btrfs_search_slot+0x492/0x1160
>>>   btrfs_lookup_csum+0xec/0x280
>>>   btrfs_csum_file_blocks+0x2be/0xa60
>>>   add_pending_csums+0xaf/0xf0
>>>   btrfs_finish_ordered_io+0x74b/0xc90
>>>   finish_ordered_fn+0x15/0x20
>>>   normal_work_helper+0xf6/0x500
>>>   btrfs_endio_write_helper+0x12/0x20
>>>   process_one_work+0x302/0x770
>>>   worker_thread+0x81/0x6d0
>>>   kthread+0x180/0x1d0
>>>   ret_from_fork+0x35/0x40
>>> ---[ end trace 2e85051acb5f6dc1 ]---
>>> ------
>>>
>>> [CAUSE]
>>> That crafted image has missing backref for csum tree root leaf.
>>> And when we try to allocate new tree block, since there is no
>>> EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
>>> and use it.
>>>
>>> However we have already locked csum tree root leaf by ourselves, thus we
>>> will ourselves to release read/write lock, and causing deadlock.
>>>
>>> [FIX]
>>> This patch will allow btrfs_tree_lock() to return error number, so
>>> most callers can exit gracefully.
>>> (Some caller doesn't really expect btrfs_tree_lock() to return error,
>>> and in that case, we use BUG_ON())
>>>
>>> Since such problem can only happen in crafted image, we will still
>>> trigger kernel warning, but with a little more meaningful warning
>>> message.
>>>
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id 0405
>>> Reported-by: Xu Wen <wen.xu@gatech.edu>
>>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>>
>> OK.. I looked through every places where the callee is called.
>> Those errors are handled gracefully as my thought.
>> Except one nitpick, the %llu about pid_t in btrfs_tree_lock.
>> However, you can add the tag:
>>
>> Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>
> 
> snip
> 
>>
>> Nit:
>> pid_t is as an signed integer, should be pid= .
> 
> BTW, how could pid be negative?
> And why my gcc doesn't give such warning?

My fault, gcc does give warning about this.
I'll fix it soon.

Thanks,
Qu

> 
> Thanks,
> Qu
> 
>>
>> Thanks,
>> Su
>>
>>> +             eb->start, current->pid);
>>> +        return -EUCLEAN;
>>> +    }
>>>   again:
>>>       wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers)
>>> =0);
>>>       wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers)
>>> =0);
>>> diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
>>> index 29135def468e..7394d7ba2ff9 100644
>>> --- a/fs/btrfs/locking.h
>>> +++ b/fs/btrfs/locking.h
>>> @@ -11,7 +11,7 @@
>>>   #define BTRFS_WRITE_LOCK_BLOCKING 3
>>>   #define BTRFS_READ_LOCK_BLOCKING 4
>>>   -void btrfs_tree_lock(struct extent_buffer *eb);
>>> +int btrfs_tree_lock(struct extent_buffer *eb);
>>>   void btrfs_tree_unlock(struct extent_buffer *eb);
>>>     void btrfs_tree_read_lock(struct extent_buffer *eb);
>>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>>> index 1874a6d2e6f5..ec4351fd7537 100644
>>> --- a/fs/btrfs/qgroup.c
>>> +++ b/fs/btrfs/qgroup.c
>>> @@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct
>>> btrfs_trans_handle *trans,
>>>         list_del(&quota_root->dirty_list);
>>>   -    btrfs_tree_lock(quota_root->node);
>>> +    ret =trfs_tree_lock(quota_root->node);
>>> +    if (ret < 0)
>>> +        goto out;
>>>       clean_tree_block(fs_info, quota_root->node);
>>>       btrfs_tree_unlock(quota_root->node);
>>>       btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
>>> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
>>> index be94c65bb4d2..a2fc0bd83a40 100644
>>> --- a/fs/btrfs/relocation.c
>>> +++ b/fs/btrfs/relocation.c
>>> @@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
>>>                   free_extent_buffer(eb);
>>>                   break;
>>>               }
>>> -            btrfs_tree_lock(eb);
>>> +            ret =trfs_tree_lock(eb);
>>> +            if (ret < 0) {
>>> +                free_extent_buffer(eb);
>>> +                break;
>>> +            }
>>>               if (cow) {
>>>                   ret =trfs_cow_block(trans, dest, eb, parent,
>>>                                 slot, &eb);
>>> @@ -2788,7 +2792,12 @@ static int do_relocation(struct
>>> btrfs_trans_handle *trans,
>>>               err =EIO;
>>>               goto next;
>>>           }
>>> -        btrfs_tree_lock(eb);
>>> +        ret =trfs_tree_lock(eb);
>>> +        if (ret < 0) {
>>> +            free_extent_buffer(eb);
>>> +            err =et;
>>> +            goto next;
>>> +        }
>>>           btrfs_set_lock_blocking(eb);
>>>             if (!node->eb) {
>>> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
>>> index f8220ec02036..173bc15a7cd1 100644
>>> --- a/fs/btrfs/tree-log.c
>>> +++ b/fs/btrfs/tree-log.c
>>> @@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct
>>> btrfs_trans_handle *trans,
>>>                   }
>>>                     if (trans) {
>>> -                    btrfs_tree_lock(next);
>>> +                    ret =trfs_tree_lock(next);
>>> +                    if (ret < 0) {
>>> +                        free_extent_buffer(next);
>>> +                        return ret;
>>> +                    }
>>>                       btrfs_set_lock_blocking(next);
>>>                       clean_tree_block(fs_info, next);
>>>                       btrfs_wait_tree_block_writeback(next);
>>> @@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct
>>> btrfs_trans_handle *trans,
>>>                   next =ath->nodes[*level];
>>>                     if (trans) {
>>> -                    btrfs_tree_lock(next);
>>> +                    ret =trfs_tree_lock(next);
>>> +                    if (ret < 0)
>>> +                        return ret;
>>>                       btrfs_set_lock_blocking(next);
>>>                       clean_tree_block(fs_info, next);
>>>                       btrfs_wait_tree_block_writeback(next);
>>> @@ -2754,7 +2760,9 @@ static int walk_log_tree(struct
>>> btrfs_trans_handle *trans,
>>>               next =ath->nodes[orig_level];
>>>                 if (trans) {
>>> -                btrfs_tree_lock(next);
>>> +                ret =trfs_tree_lock(next);
>>> +                if (ret < 0)
>>> +                    goto out;
>>>                   btrfs_set_lock_blocking(next);
>>>                   clean_tree_block(fs_info, next);
>>>                   btrfs_wait_tree_block_writeback(next);
>>>
>>
>>
>> -- 
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
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> 

Re: [PATCH 1/1] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Su Yue]

On 07/30/2018 02:17 PM, Qu Wenruo wrote:
> [BUG]
> For certains crafted image, whose csum root leaf has missing backref, if
> we try to trigger write with data csum, it could cause deadlock with the
> following kernel WARN_ON():
> ------
> WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230 btrfs_tree_lock+0x3e2/0x400
> CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
> Workqueue: btrfs-endio-write btrfs_endio_write_helper
> RIP: 0010:btrfs_tree_lock+0x3e2/0x400
> Call Trace:
>   btrfs_alloc_tree_block+0x39f/0x770
>   __btrfs_cow_block+0x285/0x9e0
>   btrfs_cow_block+0x191/0x2e0
>   btrfs_search_slot+0x492/0x1160
>   btrfs_lookup_csum+0xec/0x280
>   btrfs_csum_file_blocks+0x2be/0xa60
>   add_pending_csums+0xaf/0xf0
>   btrfs_finish_ordered_io+0x74b/0xc90
>   finish_ordered_fn+0x15/0x20
>   normal_work_helper+0xf6/0x500
>   btrfs_endio_write_helper+0x12/0x20
>   process_one_work+0x302/0x770
>   worker_thread+0x81/0x6d0
>   kthread+0x180/0x1d0
>   ret_from_fork+0x35/0x40
> ---[ end trace 2e85051acb5f6dc1 ]---
> ------
> 
> [CAUSE]
> That crafted image has missing backref for csum tree root leaf.
> And when we try to allocate new tree block, since there is no
> EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
> and use it.
> 
> However we have already locked csum tree root leaf by ourselves, thus we
> will ourselves to release read/write lock, and causing deadlock.
> 
> [FIX]
> This patch will allow btrfs_tree_lock() to return error number, so
> most callers can exit gracefully.
> (Some caller doesn't really expect btrfs_tree_lock() to return error,
> and in that case, we use BUG_ON())
> 
> Since such problem can only happen in crafted image, we will still
> trigger kernel warning, but with a little more meaningful warning
> message.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
> Reported-by: Xu Wen <wen.xu@gatech.edu>
> Signed-off-by: Qu Wenruo <wqu@suse.com>

OK.. I looked through every places where the callee is called.
Those errors are handled gracefully as my thought.
Except one nitpick, the %llu about pid_t in btrfs_tree_lock.
However, you can add the tag:

Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>

> ---
>   fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
>   fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
>   fs/btrfs/extent_io.c       |  8 ++++--
>   fs/btrfs/free-space-tree.c |  4 ++-
>   fs/btrfs/locking.c         | 12 ++++++--
>   fs/btrfs/locking.h         |  2 +-
>   fs/btrfs/qgroup.c          |  4 ++-
>   fs/btrfs/relocation.c      | 13 +++++++--
>   fs/btrfs/tree-log.c        | 14 ++++++++--
>   9 files changed, 114 insertions(+), 28 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 4bc326df472e..6e695f4cd931 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -161,10 +161,12 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
>   struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
>   {
>   	struct extent_buffer *eb;
> +	int ret;
>   
>   	while (1) {
>   		eb = btrfs_root_node(root);
> -		btrfs_tree_lock(eb);
> +		ret = btrfs_tree_lock(eb);
> +		BUG_ON(ret < 0);
>   		if (eb == root->node)
>   			break;
>   		btrfs_tree_unlock(eb);
> @@ -1584,6 +1586,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>   	for (i = start_slot; i <= end_slot; i++) {
>   		struct btrfs_key first_key;
>   		int close = 1;
> +		int ret;
>   
>   		btrfs_node_key(parent, &disk_key, i);
>   		if (!progress_passed && comp_keys(&disk_key, progress) < 0)
> @@ -1637,7 +1640,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>   		if (search_start == 0)
>   			search_start = last_block;
>   
> -		btrfs_tree_lock(cur);
> +		ret = btrfs_tree_lock(cur);
> +		if (ret < 0) {
> +			free_extent_buffer(cur);
> +			return ret;
> +		}
>   		btrfs_set_lock_blocking(cur);
>   		err = __btrfs_cow_block(trans, root, cur, parent, i,
>   					&cur, search_start,
> @@ -1853,7 +1860,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>   			goto enospc;
>   		}
>   
> -		btrfs_tree_lock(child);
> +		ret = btrfs_tree_lock(child);
> +		if (ret < 0) {
> +			free_extent_buffer(child);
> +			goto enospc;
> +		}
>   		btrfs_set_lock_blocking(child);
>   		ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
>   		if (ret) {
> @@ -1891,7 +1902,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>   		left = NULL;
>   
>   	if (left) {
> -		btrfs_tree_lock(left);
> +		ret = btrfs_tree_lock(left);
> +		if (ret < 0) {
> +			free_extent_buffer(left);
> +			left = NULL;
> +			goto enospc;
> +		}
>   		btrfs_set_lock_blocking(left);
>   		wret = btrfs_cow_block(trans, root, left,
>   				       parent, pslot - 1, &left);
> @@ -1906,7 +1922,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>   		right = NULL;
>   
>   	if (right) {
> -		btrfs_tree_lock(right);
> +		ret = btrfs_tree_lock(right);
> +		if (ret < 0) {
> +			free_extent_buffer(right);

> +			right = NULL;
> +			goto enospc;
> +		}
>   		btrfs_set_lock_blocking(right);
>   		wret = btrfs_cow_block(trans, root, right,
>   				       parent, pslot + 1, &right);
> @@ -2069,7 +2090,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>   	if (left) {
>   		u32 left_nr;
>   
> -		btrfs_tree_lock(left);
> +		ret = btrfs_tree_lock(left);
> +		if (ret < 0) {
> +			free_extent_buffer(left);
> +			return ret;
> +		}
>   		btrfs_set_lock_blocking(left);
>   
>   		left_nr = btrfs_header_nritems(left);
> @@ -2124,7 +2149,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>   	if (right) {
>   		u32 right_nr;
>   
> -		btrfs_tree_lock(right);
> +		ret = btrfs_tree_lock(right);
> +		if (ret < 0) {
> +			free_extent_buffer(right);
> +			return ret;
> +		}
>   		btrfs_set_lock_blocking(right);
>   
>   		right_nr = btrfs_header_nritems(right);
> @@ -2874,7 +2903,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>   					err = btrfs_try_tree_write_lock(b);
>   					if (!err) {
>   						btrfs_set_path_blocking(p);
> -						btrfs_tree_lock(b);
> +						ret = btrfs_tree_lock(b);
> +						if (ret < 0)
> +							goto done;
>   						btrfs_clear_path_blocking(p, b,
>   								  BTRFS_WRITE_LOCK);
>   					}
> @@ -3773,7 +3804,9 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>   	if (IS_ERR(right))
>   		return 1;
>   
> -	btrfs_tree_lock(right);
> +	ret = btrfs_tree_lock(right);
> +	if (ret < 0)
> +		goto out_free;
>   	btrfs_set_lock_blocking(right);
>   
>   	free_space = btrfs_leaf_free_space(fs_info, right);
> @@ -3811,6 +3844,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>   				right, free_space, left_nritems, min_slot);
>   out_unlock:
>   	btrfs_tree_unlock(right);
> +out_free:
>   	free_extent_buffer(right);
>   	return 1;
>   }
> @@ -4007,7 +4041,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>   	if (IS_ERR(left))
>   		return 1;
>   
> -	btrfs_tree_lock(left);
> +	ret = btrfs_tree_lock(left);
> +	if (ret < 0)
> +		goto out_free;
>   	btrfs_set_lock_blocking(left);
>   
>   	free_space = btrfs_leaf_free_space(fs_info, left);
> @@ -4037,6 +4073,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>   			       max_slot);
>   out:
>   	btrfs_tree_unlock(left);
> +out_free:
>   	free_extent_buffer(left);
>   	return ret;
>   }
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 3578fa5b30ef..da615ebc072e 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -8297,14 +8297,19 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>   {
>   	struct btrfs_fs_info *fs_info = root->fs_info;
>   	struct extent_buffer *buf;
> +	int ret;
>   
>   	buf = btrfs_find_create_tree_block(fs_info, bytenr);
>   	if (IS_ERR(buf))
>   		return buf;
> +	ret = btrfs_tree_lock(buf);
> +	if (ret < 0) {
> +		free_extent_buffer(buf);
> +		return ERR_PTR(ret);
> +	}
>   
>   	btrfs_set_header_generation(buf, trans->transid);
>   	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
> -	btrfs_tree_lock(buf);
>   	clean_tree_block(fs_info, buf);
>   	clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
>   
> @@ -8721,7 +8726,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>   					       level - 1);
>   		reada = 1;
>   	}
> -	btrfs_tree_lock(next);
> +	ret = btrfs_tree_lock(next);
> +	if (ret < 0)
> +		goto out_free;
>   	btrfs_set_lock_blocking(next);
>   
>   	ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
> @@ -8781,7 +8788,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>   			free_extent_buffer(next);
>   			return -EIO;
>   		}
> -		btrfs_tree_lock(next);
> +		ret = btrfs_tree_lock(next);
> +		if (ret < 0)
> +			goto out_free;
>   		btrfs_set_lock_blocking(next);
>   	}
>   
> @@ -8839,6 +8848,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>   
>   out_unlock:
>   	btrfs_tree_unlock(next);
> +out_free:
>   	free_extent_buffer(next);
>   
>   	return ret;
> @@ -8887,7 +8897,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>   		 */
>   		if (!path->locks[level]) {
>   			BUG_ON(level == 0);
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			BUG_ON(ret < 0);
>   			btrfs_set_lock_blocking(eb);
>   			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>   
> @@ -8929,7 +8940,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>   		/* make block locked assertion in clean_tree_block happy */
>   		if (!path->locks[level] &&
>   		    btrfs_header_generation(eb) == trans->transid) {
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			BUG_ON(ret < 0);
>   			btrfs_set_lock_blocking(eb);
>   			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>   		}
> @@ -9107,7 +9119,11 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
>   
>   		level = btrfs_header_level(root->node);
>   		while (1) {
> -			btrfs_tree_lock(path->nodes[level]);
> +			ret = btrfs_tree_lock(path->nodes[level]);
> +			if (ret < 0) {
> +				err = ret;
> +				goto out_end_trans;
> +			}
>   			btrfs_set_lock_blocking(path->nodes[level]);
>   			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>   
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index cce6087d6880..3ba02aac6dd5 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -3545,7 +3545,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>   	if (!btrfs_try_tree_write_lock(eb)) {
>   		flush = 1;
>   		flush_write_bio(epd);
> -		btrfs_tree_lock(eb);
> +		ret = btrfs_tree_lock(eb);
> +		if (ret < 0)
> +			return ret;
>   	}
>   
>   	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
> @@ -3558,7 +3560,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>   		}
>   		while (1) {
>   			wait_on_extent_buffer_writeback(eb);
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			if (ret < 0)
> +				return ret;
>   			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>   				break;
>   			btrfs_tree_unlock(eb);
> diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
> index b5950aacd697..948bbc45638a 100644
> --- a/fs/btrfs/free-space-tree.c
> +++ b/fs/btrfs/free-space-tree.c
> @@ -1242,7 +1242,9 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
>   
>   	list_del(&free_space_root->dirty_list);
>   
> -	btrfs_tree_lock(free_space_root->node);
> +	ret = btrfs_tree_lock(free_space_root->node);
> +	if (ret < 0)
> +		goto abort;
>   	clean_tree_block(fs_info, free_space_root->node);
>   	btrfs_tree_unlock(free_space_root->node);
>   	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
> diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
> index 1da768e5ef75..aa4a3362a9f1 100644
> --- a/fs/btrfs/locking.c
> +++ b/fs/btrfs/locking.c
> @@ -224,10 +224,18 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
>   /*
>    * take a spinning write lock.  This will wait for both
>    * blocking readers or writers
> + *
> + * Return 0 if we successfully locked the tree block
> + * Return <0 if some selftest failed (mostly due to extent tree corruption)
>    */
> -void btrfs_tree_lock(struct extent_buffer *eb)
> +int btrfs_tree_lock(struct extent_buffer *eb)
>   {
> -	WARN_ON(eb->lock_owner == current->pid);
> +	if (unlikely(eb->lock_owner == current->pid)) {
> +		WARN(1,
> +"tree block %llu already locked by current (pid=%llu), refuse to lock",

Nit:
pid_t is as an signed integer, should be pid=%d .

Thanks,
Su

> +		     eb->start, current->pid);
> +		return -EUCLEAN;
> +	}
>   again:
>   	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
>   	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
> diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
> index 29135def468e..7394d7ba2ff9 100644
> --- a/fs/btrfs/locking.h
> +++ b/fs/btrfs/locking.h
> @@ -11,7 +11,7 @@
>   #define BTRFS_WRITE_LOCK_BLOCKING 3
>   #define BTRFS_READ_LOCK_BLOCKING 4
>   
> -void btrfs_tree_lock(struct extent_buffer *eb);
> +int btrfs_tree_lock(struct extent_buffer *eb);
>   void btrfs_tree_unlock(struct extent_buffer *eb);
>   
>   void btrfs_tree_read_lock(struct extent_buffer *eb);
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 1874a6d2e6f5..ec4351fd7537 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
>   
>   	list_del(&quota_root->dirty_list);
>   
> -	btrfs_tree_lock(quota_root->node);
> +	ret = btrfs_tree_lock(quota_root->node);
> +	if (ret < 0)
> +		goto out;
>   	clean_tree_block(fs_info, quota_root->node);
>   	btrfs_tree_unlock(quota_root->node);
>   	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index be94c65bb4d2..a2fc0bd83a40 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
>   				free_extent_buffer(eb);
>   				break;
>   			}
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			if (ret < 0) {
> +				free_extent_buffer(eb);
> +				break;
> +			}
>   			if (cow) {
>   				ret = btrfs_cow_block(trans, dest, eb, parent,
>   						      slot, &eb);
> @@ -2788,7 +2792,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
>   			err = -EIO;
>   			goto next;
>   		}
> -		btrfs_tree_lock(eb);
> +		ret = btrfs_tree_lock(eb);
> +		if (ret < 0) {
> +			free_extent_buffer(eb);
> +			err = ret;
> +			goto next;
> +		}
>   		btrfs_set_lock_blocking(eb);
>   
>   		if (!node->eb) {
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index f8220ec02036..173bc15a7cd1 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
>   				}
>   
>   				if (trans) {
> -					btrfs_tree_lock(next);
> +					ret = btrfs_tree_lock(next);
> +					if (ret < 0) {
> +						free_extent_buffer(next);
> +						return ret;
> +					}
>   					btrfs_set_lock_blocking(next);
>   					clean_tree_block(fs_info, next);
>   					btrfs_wait_tree_block_writeback(next);
> @@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
>   				next = path->nodes[*level];
>   
>   				if (trans) {
> -					btrfs_tree_lock(next);
> +					ret = btrfs_tree_lock(next);
> +					if (ret < 0)
> +						return ret;
>   					btrfs_set_lock_blocking(next);
>   					clean_tree_block(fs_info, next);
>   					btrfs_wait_tree_block_writeback(next);
> @@ -2754,7 +2760,9 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
>   			next = path->nodes[orig_level];
>   
>   			if (trans) {
> -				btrfs_tree_lock(next);
> +				ret = btrfs_tree_lock(next);
> +				if (ret < 0)
> +					goto out;
>   				btrfs_set_lock_blocking(next);
>   				clean_tree_block(fs_info, next);
>   				btrfs_wait_tree_block_writeback(next);
> 

[PATCH v2] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

[BUG]
For certains crafted image, whose csum root leaf has missing backref, if
we try to trigger write with data csum, it could cause deadlock with the
following kernel WARN_ON():
------
WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230 btrfs_tree_lock+0x3e2/0x400
CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
Workqueue: btrfs-endio-write btrfs_endio_write_helper
RIP: 0010:btrfs_tree_lock+0x3e2/0x400
Call Trace:
 btrfs_alloc_tree_block+0x39f/0x770
 __btrfs_cow_block+0x285/0x9e0
 btrfs_cow_block+0x191/0x2e0
 btrfs_search_slot+0x492/0x1160
 btrfs_lookup_csum+0xec/0x280
 btrfs_csum_file_blocks+0x2be/0xa60
 add_pending_csums+0xaf/0xf0
 btrfs_finish_ordered_io+0x74b/0xc90
 finish_ordered_fn+0x15/0x20
 normal_work_helper+0xf6/0x500
 btrfs_endio_write_helper+0x12/0x20
 process_one_work+0x302/0x770
 worker_thread+0x81/0x6d0
 kthread+0x180/0x1d0
 ret_from_fork+0x35/0x40
---[ end trace 2e85051acb5f6dc1 ]---
------

[CAUSE]
That crafted image has missing backref for csum tree root leaf.
And when we try to allocate new tree block, since there is no
EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
and use it.

However we have already locked csum tree root leaf by ourselves, thus we
will ourselves to release read/write lock, and causing deadlock.

[FIX]
This patch will allow btrfs_tree_lock() to return error number, so
most callers can exit gracefully.
(Some caller doesn't really expect btrfs_tree_lock() to return error,
and in that case, we use BUG_ON())

Since such problem can only happen in crafted image, we will still
trigger kernel warning, but with a little more meaningful warning
message.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
Reported-by: Xu Wen <wen.xu@gatech.edu>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>
---
changelog:
v2:
  Fix pid_t output format from %llu to %d. Pointed by Su.
  Fix missing return 0 for btrfs_lock_tree().
  Update reviewed-by tags.
---
 fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
 fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
 fs/btrfs/extent_io.c       |  8 ++++--
 fs/btrfs/free-space-tree.c |  4 ++-
 fs/btrfs/locking.c         | 13 +++++++--
 fs/btrfs/locking.h         |  2 +-
 fs/btrfs/qgroup.c          |  4 ++-
 fs/btrfs/relocation.c      | 13 +++++++--
 fs/btrfs/tree-log.c        | 14 ++++++++--
 9 files changed, 115 insertions(+), 28 deletions(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 4bc326df472e..6e695f4cd931 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -161,10 +161,12 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
 {
 	struct extent_buffer *eb;
+	int ret;
 
 	while (1) {
 		eb = btrfs_root_node(root);
-		btrfs_tree_lock(eb);
+		ret = btrfs_tree_lock(eb);
+		BUG_ON(ret < 0);
 		if (eb == root->node)
 			break;
 		btrfs_tree_unlock(eb);
@@ -1584,6 +1586,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 	for (i = start_slot; i <= end_slot; i++) {
 		struct btrfs_key first_key;
 		int close = 1;
+		int ret;
 
 		btrfs_node_key(parent, &disk_key, i);
 		if (!progress_passed && comp_keys(&disk_key, progress) < 0)
@@ -1637,7 +1640,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 		if (search_start == 0)
 			search_start = last_block;
 
-		btrfs_tree_lock(cur);
+		ret = btrfs_tree_lock(cur);
+		if (ret < 0) {
+			free_extent_buffer(cur);
+			return ret;
+		}
 		btrfs_set_lock_blocking(cur);
 		err = __btrfs_cow_block(trans, root, cur, parent, i,
 					&cur, search_start,
@@ -1853,7 +1860,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 			goto enospc;
 		}
 
-		btrfs_tree_lock(child);
+		ret = btrfs_tree_lock(child);
+		if (ret < 0) {
+			free_extent_buffer(child);
+			goto enospc;
+		}
 		btrfs_set_lock_blocking(child);
 		ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
 		if (ret) {
@@ -1891,7 +1902,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		left = NULL;
 
 	if (left) {
-		btrfs_tree_lock(left);
+		ret = btrfs_tree_lock(left);
+		if (ret < 0) {
+			free_extent_buffer(left);
+			left = NULL;
+			goto enospc;
+		}
 		btrfs_set_lock_blocking(left);
 		wret = btrfs_cow_block(trans, root, left,
 				       parent, pslot - 1, &left);
@@ -1906,7 +1922,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		right = NULL;
 
 	if (right) {
-		btrfs_tree_lock(right);
+		ret = btrfs_tree_lock(right);
+		if (ret < 0) {
+			free_extent_buffer(right);
+			right = NULL;
+			goto enospc;
+		}
 		btrfs_set_lock_blocking(right);
 		wret = btrfs_cow_block(trans, root, right,
 				       parent, pslot + 1, &right);
@@ -2069,7 +2090,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 	if (left) {
 		u32 left_nr;
 
-		btrfs_tree_lock(left);
+		ret = btrfs_tree_lock(left);
+		if (ret < 0) {
+			free_extent_buffer(left);
+			return ret;
+		}
 		btrfs_set_lock_blocking(left);
 
 		left_nr = btrfs_header_nritems(left);
@@ -2124,7 +2149,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 	if (right) {
 		u32 right_nr;
 
-		btrfs_tree_lock(right);
+		ret = btrfs_tree_lock(right);
+		if (ret < 0) {
+			free_extent_buffer(right);
+			return ret;
+		}
 		btrfs_set_lock_blocking(right);
 
 		right_nr = btrfs_header_nritems(right);
@@ -2874,7 +2903,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 					err = btrfs_try_tree_write_lock(b);
 					if (!err) {
 						btrfs_set_path_blocking(p);
-						btrfs_tree_lock(b);
+						ret = btrfs_tree_lock(b);
+						if (ret < 0)
+							goto done;
 						btrfs_clear_path_blocking(p, b,
 								  BTRFS_WRITE_LOCK);
 					}
@@ -3773,7 +3804,9 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 	if (IS_ERR(right))
 		return 1;
 
-	btrfs_tree_lock(right);
+	ret = btrfs_tree_lock(right);
+	if (ret < 0)
+		goto out_free;
 	btrfs_set_lock_blocking(right);
 
 	free_space = btrfs_leaf_free_space(fs_info, right);
@@ -3811,6 +3844,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 				right, free_space, left_nritems, min_slot);
 out_unlock:
 	btrfs_tree_unlock(right);
+out_free:
 	free_extent_buffer(right);
 	return 1;
 }
@@ -4007,7 +4041,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 	if (IS_ERR(left))
 		return 1;
 
-	btrfs_tree_lock(left);
+	ret = btrfs_tree_lock(left);
+	if (ret < 0)
+		goto out_free;
 	btrfs_set_lock_blocking(left);
 
 	free_space = btrfs_leaf_free_space(fs_info, left);
@@ -4037,6 +4073,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 			       max_slot);
 out:
 	btrfs_tree_unlock(left);
+out_free:
 	free_extent_buffer(left);
 	return ret;
 }
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3578fa5b30ef..da615ebc072e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8297,14 +8297,19 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct extent_buffer *buf;
+	int ret;
 
 	buf = btrfs_find_create_tree_block(fs_info, bytenr);
 	if (IS_ERR(buf))
 		return buf;
+	ret = btrfs_tree_lock(buf);
+	if (ret < 0) {
+		free_extent_buffer(buf);
+		return ERR_PTR(ret);
+	}
 
 	btrfs_set_header_generation(buf, trans->transid);
 	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
-	btrfs_tree_lock(buf);
 	clean_tree_block(fs_info, buf);
 	clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
 
@@ -8721,7 +8726,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 					       level - 1);
 		reada = 1;
 	}
-	btrfs_tree_lock(next);
+	ret = btrfs_tree_lock(next);
+	if (ret < 0)
+		goto out_free;
 	btrfs_set_lock_blocking(next);
 
 	ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
@@ -8781,7 +8788,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 			free_extent_buffer(next);
 			return -EIO;
 		}
-		btrfs_tree_lock(next);
+		ret = btrfs_tree_lock(next);
+		if (ret < 0)
+			goto out_free;
 		btrfs_set_lock_blocking(next);
 	}
 
@@ -8839,6 +8848,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
 
 out_unlock:
 	btrfs_tree_unlock(next);
+out_free:
 	free_extent_buffer(next);
 
 	return ret;
@@ -8887,7 +8897,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 		 */
 		if (!path->locks[level]) {
 			BUG_ON(level == 0);
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			BUG_ON(ret < 0);
 			btrfs_set_lock_blocking(eb);
 			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 
@@ -8929,7 +8940,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 		/* make block locked assertion in clean_tree_block happy */
 		if (!path->locks[level] &&
 		    btrfs_header_generation(eb) == trans->transid) {
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			BUG_ON(ret < 0);
 			btrfs_set_lock_blocking(eb);
 			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 		}
@@ -9107,7 +9119,11 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
 
 		level = btrfs_header_level(root->node);
 		while (1) {
-			btrfs_tree_lock(path->nodes[level]);
+			ret = btrfs_tree_lock(path->nodes[level]);
+			if (ret < 0) {
+				err = ret;
+				goto out_end_trans;
+			}
 			btrfs_set_lock_blocking(path->nodes[level]);
 			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index cce6087d6880..3ba02aac6dd5 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3545,7 +3545,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
 	if (!btrfs_try_tree_write_lock(eb)) {
 		flush = 1;
 		flush_write_bio(epd);
-		btrfs_tree_lock(eb);
+		ret = btrfs_tree_lock(eb);
+		if (ret < 0)
+			return ret;
 	}
 
 	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
@@ -3558,7 +3560,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
 		}
 		while (1) {
 			wait_on_extent_buffer_writeback(eb);
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			if (ret < 0)
+				return ret;
 			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
 				break;
 			btrfs_tree_unlock(eb);
diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index b5950aacd697..948bbc45638a 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -1242,7 +1242,9 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
 
 	list_del(&free_space_root->dirty_list);
 
-	btrfs_tree_lock(free_space_root->node);
+	ret = btrfs_tree_lock(free_space_root->node);
+	if (ret < 0)
+		goto abort;
 	clean_tree_block(fs_info, free_space_root->node);
 	btrfs_tree_unlock(free_space_root->node);
 	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 1da768e5ef75..ca151be026bf 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -224,10 +224,18 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
 /*
  * take a spinning write lock.  This will wait for both
  * blocking readers or writers
+ *
+ * Return 0 if we successfully locked the tree block
+ * Return <0 if some selftest failed (mostly due to extent tree corruption)
  */
-void btrfs_tree_lock(struct extent_buffer *eb)
+int btrfs_tree_lock(struct extent_buffer *eb)
 {
-	WARN_ON(eb->lock_owner == current->pid);
+	if (unlikely(eb->lock_owner == current->pid)) {
+		WARN(1,
+"tree block %llu already locked by current (pid=%d), refuse to lock",
+		     eb->start, current->pid);
+		return -EUCLEAN;
+	}
 again:
 	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
 	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
@@ -248,6 +256,7 @@ void btrfs_tree_lock(struct extent_buffer *eb)
 	atomic_inc(&eb->spinning_writers);
 	atomic_inc(&eb->write_locks);
 	eb->lock_owner = current->pid;
+	return 0;
 }
 
 /*
diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
index 29135def468e..7394d7ba2ff9 100644
--- a/fs/btrfs/locking.h
+++ b/fs/btrfs/locking.h
@@ -11,7 +11,7 @@
 #define BTRFS_WRITE_LOCK_BLOCKING 3
 #define BTRFS_READ_LOCK_BLOCKING 4
 
-void btrfs_tree_lock(struct extent_buffer *eb);
+int btrfs_tree_lock(struct extent_buffer *eb);
 void btrfs_tree_unlock(struct extent_buffer *eb);
 
 void btrfs_tree_read_lock(struct extent_buffer *eb);
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 1874a6d2e6f5..ec4351fd7537 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
 
 	list_del(&quota_root->dirty_list);
 
-	btrfs_tree_lock(quota_root->node);
+	ret = btrfs_tree_lock(quota_root->node);
+	if (ret < 0)
+		goto out;
 	clean_tree_block(fs_info, quota_root->node);
 	btrfs_tree_unlock(quota_root->node);
 	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index be94c65bb4d2..a2fc0bd83a40 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
 				free_extent_buffer(eb);
 				break;
 			}
-			btrfs_tree_lock(eb);
+			ret = btrfs_tree_lock(eb);
+			if (ret < 0) {
+				free_extent_buffer(eb);
+				break;
+			}
 			if (cow) {
 				ret = btrfs_cow_block(trans, dest, eb, parent,
 						      slot, &eb);
@@ -2788,7 +2792,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
 			err = -EIO;
 			goto next;
 		}
-		btrfs_tree_lock(eb);
+		ret = btrfs_tree_lock(eb);
+		if (ret < 0) {
+			free_extent_buffer(eb);
+			err = ret;
+			goto next;
+		}
 		btrfs_set_lock_blocking(eb);
 
 		if (!node->eb) {
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index f8220ec02036..173bc15a7cd1 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
 				}
 
 				if (trans) {
-					btrfs_tree_lock(next);
+					ret = btrfs_tree_lock(next);
+					if (ret < 0) {
+						free_extent_buffer(next);
+						return ret;
+					}
 					btrfs_set_lock_blocking(next);
 					clean_tree_block(fs_info, next);
 					btrfs_wait_tree_block_writeback(next);
@@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
 				next = path->nodes[*level];
 
 				if (trans) {
-					btrfs_tree_lock(next);
+					ret = btrfs_tree_lock(next);
+					if (ret < 0)
+						return ret;
 					btrfs_set_lock_blocking(next);
 					clean_tree_block(fs_info, next);
 					btrfs_wait_tree_block_writeback(next);
@@ -2754,7 +2760,9 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
 			next = path->nodes[orig_level];
 
 			if (trans) {
-				btrfs_tree_lock(next);
+				ret = btrfs_tree_lock(next);
+				if (ret < 0)
+					goto out;
 				btrfs_set_lock_blocking(next);
 				clean_tree_block(fs_info, next);
 				btrfs_wait_tree_block_writeback(next);
-- 
2.18.0

Re: [PATCH v2] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[David Sterba]

On Tue, Jul 31, 2018 at 02:52:23PM +0800, Qu Wenruo wrote:
> [BUG]
> For certains crafted image, whose csum root leaf has missing backref, if
> we try to trigger write with data csum, it could cause deadlock with the
> following kernel WARN_ON():
> ------
> WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230 btrfs_tree_lock+0x3e2/0x400
> CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
> Workqueue: btrfs-endio-write btrfs_endio_write_helper
> RIP: 0010:btrfs_tree_lock+0x3e2/0x400
> Call Trace:
>  btrfs_alloc_tree_block+0x39f/0x770
>  __btrfs_cow_block+0x285/0x9e0
>  btrfs_cow_block+0x191/0x2e0
>  btrfs_search_slot+0x492/0x1160
>  btrfs_lookup_csum+0xec/0x280
>  btrfs_csum_file_blocks+0x2be/0xa60
>  add_pending_csums+0xaf/0xf0
>  btrfs_finish_ordered_io+0x74b/0xc90
>  finish_ordered_fn+0x15/0x20
>  normal_work_helper+0xf6/0x500
>  btrfs_endio_write_helper+0x12/0x20
>  process_one_work+0x302/0x770
>  worker_thread+0x81/0x6d0
>  kthread+0x180/0x1d0
>  ret_from_fork+0x35/0x40
> ---[ end trace 2e85051acb5f6dc1 ]---
> ------
> 
> [CAUSE]
> That crafted image has missing backref for csum tree root leaf.
> And when we try to allocate new tree block, since there is no
> EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
> and use it.

I don't understand what exactly is the problem, can you please rephrase
that? Ie. what exactly is missing from where. If the problem is on the
higher level, regarding the csum tree, this could be checked much
earlier. I don't really like to see each and every callsite of tree
locks to require the error handling, so I'm exploring the possibilities
if this is necessary at all.

> However we have already locked csum tree root leaf by ourselves, thus we
> will ourselves to release read/write lock, and causing deadlock.
> 
> [FIX]
> This patch will allow btrfs_tree_lock() to return error number, so
> most callers can exit gracefully.
> (Some caller doesn't really expect btrfs_tree_lock() to return error,
> and in that case, we use BUG_ON())
> 
> Since such problem can only happen in crafted image, we will still
> trigger kernel warning, but with a little more meaningful warning
> message.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
> Reported-by: Xu Wen <wen.xu@gatech.edu>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>
> ---
> changelog:
> v2:
>   Fix pid_t output format from %llu to %d. Pointed by Su.
>   Fix missing return 0 for btrfs_lock_tree().
>   Update reviewed-by tags.
> ---
>  fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
>  fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
>  fs/btrfs/extent_io.c       |  8 ++++--
>  fs/btrfs/free-space-tree.c |  4 ++-
>  fs/btrfs/locking.c         | 13 +++++++--
>  fs/btrfs/locking.h         |  2 +-
>  fs/btrfs/qgroup.c          |  4 ++-
>  fs/btrfs/relocation.c      | 13 +++++++--
>  fs/btrfs/tree-log.c        | 14 ++++++++--
>  9 files changed, 115 insertions(+), 28 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 4bc326df472e..6e695f4cd931 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -161,10 +161,12 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
>  struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
>  {
>  	struct extent_buffer *eb;
> +	int ret;
>  
>  	while (1) {
>  		eb = btrfs_root_node(root);
> -		btrfs_tree_lock(eb);
> +		ret = btrfs_tree_lock(eb);
> +		BUG_ON(ret < 0);
>  		if (eb == root->node)
>  			break;
>  		btrfs_tree_unlock(eb);
> @@ -1584,6 +1586,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>  	for (i = start_slot; i <= end_slot; i++) {
>  		struct btrfs_key first_key;
>  		int close = 1;
> +		int ret;
>  
>  		btrfs_node_key(parent, &disk_key, i);
>  		if (!progress_passed && comp_keys(&disk_key, progress) < 0)
> @@ -1637,7 +1640,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>  		if (search_start == 0)
>  			search_start = last_block;
>  
> -		btrfs_tree_lock(cur);
> +		ret = btrfs_tree_lock(cur);
> +		if (ret < 0) {
> +			free_extent_buffer(cur);
> +			return ret;
> +		}
>  		btrfs_set_lock_blocking(cur);
>  		err = __btrfs_cow_block(trans, root, cur, parent, i,
>  					&cur, search_start,
> @@ -1853,7 +1860,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>  			goto enospc;
>  		}
>  
> -		btrfs_tree_lock(child);
> +		ret = btrfs_tree_lock(child);
> +		if (ret < 0) {
> +			free_extent_buffer(child);
> +			goto enospc;
> +		}
>  		btrfs_set_lock_blocking(child);
>  		ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
>  		if (ret) {
> @@ -1891,7 +1902,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>  		left = NULL;
>  
>  	if (left) {
> -		btrfs_tree_lock(left);
> +		ret = btrfs_tree_lock(left);
> +		if (ret < 0) {
> +			free_extent_buffer(left);
> +			left = NULL;
> +			goto enospc;
> +		}
>  		btrfs_set_lock_blocking(left);
>  		wret = btrfs_cow_block(trans, root, left,
>  				       parent, pslot - 1, &left);
> @@ -1906,7 +1922,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>  		right = NULL;
>  
>  	if (right) {
> -		btrfs_tree_lock(right);
> +		ret = btrfs_tree_lock(right);
> +		if (ret < 0) {
> +			free_extent_buffer(right);
> +			right = NULL;
> +			goto enospc;
> +		}
>  		btrfs_set_lock_blocking(right);
>  		wret = btrfs_cow_block(trans, root, right,
>  				       parent, pslot + 1, &right);
> @@ -2069,7 +2090,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>  	if (left) {
>  		u32 left_nr;
>  
> -		btrfs_tree_lock(left);
> +		ret = btrfs_tree_lock(left);
> +		if (ret < 0) {
> +			free_extent_buffer(left);
> +			return ret;
> +		}
>  		btrfs_set_lock_blocking(left);
>  
>  		left_nr = btrfs_header_nritems(left);
> @@ -2124,7 +2149,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>  	if (right) {
>  		u32 right_nr;
>  
> -		btrfs_tree_lock(right);
> +		ret = btrfs_tree_lock(right);
> +		if (ret < 0) {
> +			free_extent_buffer(right);
> +			return ret;
> +		}
>  		btrfs_set_lock_blocking(right);
>  
>  		right_nr = btrfs_header_nritems(right);
> @@ -2874,7 +2903,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>  					err = btrfs_try_tree_write_lock(b);
>  					if (!err) {
>  						btrfs_set_path_blocking(p);
> -						btrfs_tree_lock(b);
> +						ret = btrfs_tree_lock(b);
> +						if (ret < 0)
> +							goto done;
>  						btrfs_clear_path_blocking(p, b,
>  								  BTRFS_WRITE_LOCK);
>  					}
> @@ -3773,7 +3804,9 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>  	if (IS_ERR(right))
>  		return 1;
>  
> -	btrfs_tree_lock(right);
> +	ret = btrfs_tree_lock(right);
> +	if (ret < 0)
> +		goto out_free;
>  	btrfs_set_lock_blocking(right);
>  
>  	free_space = btrfs_leaf_free_space(fs_info, right);
> @@ -3811,6 +3844,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>  				right, free_space, left_nritems, min_slot);
>  out_unlock:
>  	btrfs_tree_unlock(right);
> +out_free:
>  	free_extent_buffer(right);
>  	return 1;
>  }
> @@ -4007,7 +4041,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>  	if (IS_ERR(left))
>  		return 1;
>  
> -	btrfs_tree_lock(left);
> +	ret = btrfs_tree_lock(left);
> +	if (ret < 0)
> +		goto out_free;
>  	btrfs_set_lock_blocking(left);
>  
>  	free_space = btrfs_leaf_free_space(fs_info, left);
> @@ -4037,6 +4073,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>  			       max_slot);
>  out:
>  	btrfs_tree_unlock(left);
> +out_free:
>  	free_extent_buffer(left);
>  	return ret;
>  }
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 3578fa5b30ef..da615ebc072e 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -8297,14 +8297,19 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>  {
>  	struct btrfs_fs_info *fs_info = root->fs_info;
>  	struct extent_buffer *buf;
> +	int ret;
>  
>  	buf = btrfs_find_create_tree_block(fs_info, bytenr);
>  	if (IS_ERR(buf))
>  		return buf;
> +	ret = btrfs_tree_lock(buf);
> +	if (ret < 0) {
> +		free_extent_buffer(buf);
> +		return ERR_PTR(ret);
> +	}
>  
>  	btrfs_set_header_generation(buf, trans->transid);
>  	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
> -	btrfs_tree_lock(buf);
>  	clean_tree_block(fs_info, buf);
>  	clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
>  
> @@ -8721,7 +8726,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>  					       level - 1);
>  		reada = 1;
>  	}
> -	btrfs_tree_lock(next);
> +	ret = btrfs_tree_lock(next);
> +	if (ret < 0)
> +		goto out_free;
>  	btrfs_set_lock_blocking(next);
>  
>  	ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
> @@ -8781,7 +8788,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>  			free_extent_buffer(next);
>  			return -EIO;
>  		}
> -		btrfs_tree_lock(next);
> +		ret = btrfs_tree_lock(next);
> +		if (ret < 0)
> +			goto out_free;
>  		btrfs_set_lock_blocking(next);
>  	}
>  
> @@ -8839,6 +8848,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>  
>  out_unlock:
>  	btrfs_tree_unlock(next);
> +out_free:
>  	free_extent_buffer(next);
>  
>  	return ret;
> @@ -8887,7 +8897,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>  		 */
>  		if (!path->locks[level]) {
>  			BUG_ON(level == 0);
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			BUG_ON(ret < 0);
>  			btrfs_set_lock_blocking(eb);
>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>  
> @@ -8929,7 +8940,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>  		/* make block locked assertion in clean_tree_block happy */
>  		if (!path->locks[level] &&
>  		    btrfs_header_generation(eb) == trans->transid) {
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			BUG_ON(ret < 0);
>  			btrfs_set_lock_blocking(eb);
>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>  		}
> @@ -9107,7 +9119,11 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
>  
>  		level = btrfs_header_level(root->node);
>  		while (1) {
> -			btrfs_tree_lock(path->nodes[level]);
> +			ret = btrfs_tree_lock(path->nodes[level]);
> +			if (ret < 0) {
> +				err = ret;
> +				goto out_end_trans;
> +			}
>  			btrfs_set_lock_blocking(path->nodes[level]);
>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>  
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index cce6087d6880..3ba02aac6dd5 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -3545,7 +3545,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>  	if (!btrfs_try_tree_write_lock(eb)) {
>  		flush = 1;
>  		flush_write_bio(epd);
> -		btrfs_tree_lock(eb);
> +		ret = btrfs_tree_lock(eb);
> +		if (ret < 0)
> +			return ret;
>  	}
>  
>  	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
> @@ -3558,7 +3560,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>  		}
>  		while (1) {
>  			wait_on_extent_buffer_writeback(eb);
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			if (ret < 0)
> +				return ret;
>  			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>  				break;
>  			btrfs_tree_unlock(eb);
> diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
> index b5950aacd697..948bbc45638a 100644
> --- a/fs/btrfs/free-space-tree.c
> +++ b/fs/btrfs/free-space-tree.c
> @@ -1242,7 +1242,9 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
>  
>  	list_del(&free_space_root->dirty_list);
>  
> -	btrfs_tree_lock(free_space_root->node);
> +	ret = btrfs_tree_lock(free_space_root->node);
> +	if (ret < 0)
> +		goto abort;
>  	clean_tree_block(fs_info, free_space_root->node);
>  	btrfs_tree_unlock(free_space_root->node);
>  	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
> diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
> index 1da768e5ef75..ca151be026bf 100644
> --- a/fs/btrfs/locking.c
> +++ b/fs/btrfs/locking.c
> @@ -224,10 +224,18 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
>  /*
>   * take a spinning write lock.  This will wait for both
>   * blocking readers or writers
> + *
> + * Return 0 if we successfully locked the tree block
> + * Return <0 if some selftest failed (mostly due to extent tree corruption)
>   */
> -void btrfs_tree_lock(struct extent_buffer *eb)
> +int btrfs_tree_lock(struct extent_buffer *eb)
>  {
> -	WARN_ON(eb->lock_owner == current->pid);
> +	if (unlikely(eb->lock_owner == current->pid)) {
> +		WARN(1,
> +"tree block %llu already locked by current (pid=%d), refuse to lock",
> +		     eb->start, current->pid);
> +		return -EUCLEAN;
> +	}
>  again:
>  	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
>  	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
> @@ -248,6 +256,7 @@ void btrfs_tree_lock(struct extent_buffer *eb)
>  	atomic_inc(&eb->spinning_writers);
>  	atomic_inc(&eb->write_locks);
>  	eb->lock_owner = current->pid;
> +	return 0;
>  }
>  
>  /*
> diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
> index 29135def468e..7394d7ba2ff9 100644
> --- a/fs/btrfs/locking.h
> +++ b/fs/btrfs/locking.h
> @@ -11,7 +11,7 @@
>  #define BTRFS_WRITE_LOCK_BLOCKING 3
>  #define BTRFS_READ_LOCK_BLOCKING 4
>  
> -void btrfs_tree_lock(struct extent_buffer *eb);
> +int btrfs_tree_lock(struct extent_buffer *eb);
>  void btrfs_tree_unlock(struct extent_buffer *eb);
>  
>  void btrfs_tree_read_lock(struct extent_buffer *eb);
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 1874a6d2e6f5..ec4351fd7537 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
>  
>  	list_del(&quota_root->dirty_list);
>  
> -	btrfs_tree_lock(quota_root->node);
> +	ret = btrfs_tree_lock(quota_root->node);
> +	if (ret < 0)
> +		goto out;
>  	clean_tree_block(fs_info, quota_root->node);
>  	btrfs_tree_unlock(quota_root->node);
>  	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index be94c65bb4d2..a2fc0bd83a40 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
>  				free_extent_buffer(eb);
>  				break;
>  			}
> -			btrfs_tree_lock(eb);
> +			ret = btrfs_tree_lock(eb);
> +			if (ret < 0) {
> +				free_extent_buffer(eb);
> +				break;
> +			}
>  			if (cow) {
>  				ret = btrfs_cow_block(trans, dest, eb, parent,
>  						      slot, &eb);
> @@ -2788,7 +2792,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
>  			err = -EIO;
>  			goto next;
>  		}
> -		btrfs_tree_lock(eb);
> +		ret = btrfs_tree_lock(eb);
> +		if (ret < 0) {
> +			free_extent_buffer(eb);
> +			err = ret;
> +			goto next;
> +		}
>  		btrfs_set_lock_blocking(eb);
>  
>  		if (!node->eb) {
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index f8220ec02036..173bc15a7cd1 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
>  				}
>  
>  				if (trans) {
> -					btrfs_tree_lock(next);
> +					ret = btrfs_tree_lock(next);
> +					if (ret < 0) {
> +						free_extent_buffer(next);
> +						return ret;
> +					}
>  					btrfs_set_lock_blocking(next);
>  					clean_tree_block(fs_info, next);
>  					btrfs_wait_tree_block_writeback(next);
> @@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
>  				next = path->nodes[*level];
>  
>  				if (trans) {
> -					btrfs_tree_lock(next);
> +					ret = btrfs_tree_lock(next);
> +					if (ret < 0)
> +						return ret;
>  					btrfs_set_lock_blocking(next);
>  					clean_tree_block(fs_info, next);
>  					btrfs_wait_tree_block_writeback(next);
> @@ -2754,7 +2760,9 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
>  			next = path->nodes[orig_level];
>  
>  			if (trans) {
> -				btrfs_tree_lock(next);
> +				ret = btrfs_tree_lock(next);
> +				if (ret < 0)
> +					goto out;
>  				btrfs_set_lock_blocking(next);
>  				clean_tree_block(fs_info, next);
>  				btrfs_wait_tree_block_writeback(next);
> -- 
> 2.18.0
> 
> --
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Re: [PATCH v2] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

[-- Attachment #1.1: Type: text/plain, Size: 19673 bytes --]



On 2018年08月01日 21:27, David Sterba wrote:
> On Tue, Jul 31, 2018 at 02:52:23PM +0800, Qu Wenruo wrote:
>> [BUG]
>> For certains crafted image, whose csum root leaf has missing backref, if
>> we try to trigger write with data csum, it could cause deadlock with the
>> following kernel WARN_ON():
>> ------
>> WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230 btrfs_tree_lock+0x3e2/0x400
>> CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
>> Workqueue: btrfs-endio-write btrfs_endio_write_helper
>> RIP: 0010:btrfs_tree_lock+0x3e2/0x400
>> Call Trace:
>>  btrfs_alloc_tree_block+0x39f/0x770
>>  __btrfs_cow_block+0x285/0x9e0
>>  btrfs_cow_block+0x191/0x2e0
>>  btrfs_search_slot+0x492/0x1160
>>  btrfs_lookup_csum+0xec/0x280
>>  btrfs_csum_file_blocks+0x2be/0xa60
>>  add_pending_csums+0xaf/0xf0
>>  btrfs_finish_ordered_io+0x74b/0xc90
>>  finish_ordered_fn+0x15/0x20
>>  normal_work_helper+0xf6/0x500
>>  btrfs_endio_write_helper+0x12/0x20
>>  process_one_work+0x302/0x770
>>  worker_thread+0x81/0x6d0
>>  kthread+0x180/0x1d0
>>  ret_from_fork+0x35/0x40
>> ---[ end trace 2e85051acb5f6dc1 ]---
>> ------
>>
>> [CAUSE]
>> That crafted image has missing backref for csum tree root leaf.
>> And when we try to allocate new tree block, since there is no
>> EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
>> and use it.
> 
> I don't understand what exactly is the problem, can you please rephrase
> that? Ie. what exactly is missing from where. If the problem is on the
> higher level, regarding the csum tree, this could be checked much
> earlier. I don't really like to see each and every callsite of tree
> locks to require the error handling, so I'm exploring the possibilities
> if this is necessary at all.

This is a little complex.

I'll try to explain this using some asciiart:

Normal image                      |       This fuzzed image
----------------------------------+--------------------------------
BG 29360128                       | BG 29360128
 One empty slot                   |  One empty slot
29364224: backref to UUID tree    | 29364224: backref to UUID tree
 Two empty slots                  |  Two empty slots
29376512: backref to CSUM tree    |  One empty slot (bad type)
29380608: backref to D_RELOC tree | 29380608: backref to D_RELOC tree
...                               | ...

Since bytenr 29376512 has no METADATA/EXTENT_ITEM, when btrfs try to
alloc tree block, it's an valid slot for btrfs.

And for finish_ordered_write, when we need to insert csum, we try to CoW
csum tree root.

Then extent allocator gives a new extent bytenr 29376512 length 4096.
However bytenr 29376512 is our current csum root, and already locked
during CoW.

So in btrfs_alloc_tree_block() which calls btrfs_tree_lock() to lock the
newly allocated tree block, we are trying to lock the tree block we have
already locked, thus triggering the WARN_ON() and deadlock.


In this particular fuzzed image, we can do key type check to detect
early corruption, but it has the following problem:

1) Won't really solve the problem
   I could easily craft a image with backref for csum tree missing, and
   everything else is OK. It will still cause the problem.

2) May break later RO_compat features
   If later RO_compat feature introduces new key type in extent tree, in
   theory it should be able to be mounted RO, but will be rejected by
   the type check.

So we have to go the way used in the patch.

Another solution would be do backref check each time we try to read out
a tree block, but that's too costly and may screw up locking.

Thanks,
Qu

> 
>> However we have already locked csum tree root leaf by ourselves, thus we
>> will ourselves to release read/write lock, and causing deadlock.
>>
>> [FIX]
>> This patch will allow btrfs_tree_lock() to return error number, so
>> most callers can exit gracefully.
>> (Some caller doesn't really expect btrfs_tree_lock() to return error,
>> and in that case, we use BUG_ON())
>>
>> Since such problem can only happen in crafted image, we will still
>> trigger kernel warning, but with a little more meaningful warning
>> message.
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
>> Reported-by: Xu Wen <wen.xu@gatech.edu>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>
>> ---
>> changelog:
>> v2:
>>   Fix pid_t output format from %llu to %d. Pointed by Su.
>>   Fix missing return 0 for btrfs_lock_tree().
>>   Update reviewed-by tags.
>> ---
>>  fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
>>  fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
>>  fs/btrfs/extent_io.c       |  8 ++++--
>>  fs/btrfs/free-space-tree.c |  4 ++-
>>  fs/btrfs/locking.c         | 13 +++++++--
>>  fs/btrfs/locking.h         |  2 +-
>>  fs/btrfs/qgroup.c          |  4 ++-
>>  fs/btrfs/relocation.c      | 13 +++++++--
>>  fs/btrfs/tree-log.c        | 14 ++++++++--
>>  9 files changed, 115 insertions(+), 28 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>> index 4bc326df472e..6e695f4cd931 100644
>> --- a/fs/btrfs/ctree.c
>> +++ b/fs/btrfs/ctree.c
>> @@ -161,10 +161,12 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
>>  struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
>>  {
>>  	struct extent_buffer *eb;
>> +	int ret;
>>  
>>  	while (1) {
>>  		eb = btrfs_root_node(root);
>> -		btrfs_tree_lock(eb);
>> +		ret = btrfs_tree_lock(eb);
>> +		BUG_ON(ret < 0);
>>  		if (eb == root->node)
>>  			break;
>>  		btrfs_tree_unlock(eb);
>> @@ -1584,6 +1586,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>>  	for (i = start_slot; i <= end_slot; i++) {
>>  		struct btrfs_key first_key;
>>  		int close = 1;
>> +		int ret;
>>  
>>  		btrfs_node_key(parent, &disk_key, i);
>>  		if (!progress_passed && comp_keys(&disk_key, progress) < 0)
>> @@ -1637,7 +1640,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>>  		if (search_start == 0)
>>  			search_start = last_block;
>>  
>> -		btrfs_tree_lock(cur);
>> +		ret = btrfs_tree_lock(cur);
>> +		if (ret < 0) {
>> +			free_extent_buffer(cur);
>> +			return ret;
>> +		}
>>  		btrfs_set_lock_blocking(cur);
>>  		err = __btrfs_cow_block(trans, root, cur, parent, i,
>>  					&cur, search_start,
>> @@ -1853,7 +1860,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>  			goto enospc;
>>  		}
>>  
>> -		btrfs_tree_lock(child);
>> +		ret = btrfs_tree_lock(child);
>> +		if (ret < 0) {
>> +			free_extent_buffer(child);
>> +			goto enospc;
>> +		}
>>  		btrfs_set_lock_blocking(child);
>>  		ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
>>  		if (ret) {
>> @@ -1891,7 +1902,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>  		left = NULL;
>>  
>>  	if (left) {
>> -		btrfs_tree_lock(left);
>> +		ret = btrfs_tree_lock(left);
>> +		if (ret < 0) {
>> +			free_extent_buffer(left);
>> +			left = NULL;
>> +			goto enospc;
>> +		}
>>  		btrfs_set_lock_blocking(left);
>>  		wret = btrfs_cow_block(trans, root, left,
>>  				       parent, pslot - 1, &left);
>> @@ -1906,7 +1922,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>  		right = NULL;
>>  
>>  	if (right) {
>> -		btrfs_tree_lock(right);
>> +		ret = btrfs_tree_lock(right);
>> +		if (ret < 0) {
>> +			free_extent_buffer(right);
>> +			right = NULL;
>> +			goto enospc;
>> +		}
>>  		btrfs_set_lock_blocking(right);
>>  		wret = btrfs_cow_block(trans, root, right,
>>  				       parent, pslot + 1, &right);
>> @@ -2069,7 +2090,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>  	if (left) {
>>  		u32 left_nr;
>>  
>> -		btrfs_tree_lock(left);
>> +		ret = btrfs_tree_lock(left);
>> +		if (ret < 0) {
>> +			free_extent_buffer(left);
>> +			return ret;
>> +		}
>>  		btrfs_set_lock_blocking(left);
>>  
>>  		left_nr = btrfs_header_nritems(left);
>> @@ -2124,7 +2149,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>  	if (right) {
>>  		u32 right_nr;
>>  
>> -		btrfs_tree_lock(right);
>> +		ret = btrfs_tree_lock(right);
>> +		if (ret < 0) {
>> +			free_extent_buffer(right);
>> +			return ret;
>> +		}
>>  		btrfs_set_lock_blocking(right);
>>  
>>  		right_nr = btrfs_header_nritems(right);
>> @@ -2874,7 +2903,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>>  					err = btrfs_try_tree_write_lock(b);
>>  					if (!err) {
>>  						btrfs_set_path_blocking(p);
>> -						btrfs_tree_lock(b);
>> +						ret = btrfs_tree_lock(b);
>> +						if (ret < 0)
>> +							goto done;
>>  						btrfs_clear_path_blocking(p, b,
>>  								  BTRFS_WRITE_LOCK);
>>  					}
>> @@ -3773,7 +3804,9 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>>  	if (IS_ERR(right))
>>  		return 1;
>>  
>> -	btrfs_tree_lock(right);
>> +	ret = btrfs_tree_lock(right);
>> +	if (ret < 0)
>> +		goto out_free;
>>  	btrfs_set_lock_blocking(right);
>>  
>>  	free_space = btrfs_leaf_free_space(fs_info, right);
>> @@ -3811,6 +3844,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>>  				right, free_space, left_nritems, min_slot);
>>  out_unlock:
>>  	btrfs_tree_unlock(right);
>> +out_free:
>>  	free_extent_buffer(right);
>>  	return 1;
>>  }
>> @@ -4007,7 +4041,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>>  	if (IS_ERR(left))
>>  		return 1;
>>  
>> -	btrfs_tree_lock(left);
>> +	ret = btrfs_tree_lock(left);
>> +	if (ret < 0)
>> +		goto out_free;
>>  	btrfs_set_lock_blocking(left);
>>  
>>  	free_space = btrfs_leaf_free_space(fs_info, left);
>> @@ -4037,6 +4073,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>>  			       max_slot);
>>  out:
>>  	btrfs_tree_unlock(left);
>> +out_free:
>>  	free_extent_buffer(left);
>>  	return ret;
>>  }
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 3578fa5b30ef..da615ebc072e 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -8297,14 +8297,19 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>>  {
>>  	struct btrfs_fs_info *fs_info = root->fs_info;
>>  	struct extent_buffer *buf;
>> +	int ret;
>>  
>>  	buf = btrfs_find_create_tree_block(fs_info, bytenr);
>>  	if (IS_ERR(buf))
>>  		return buf;
>> +	ret = btrfs_tree_lock(buf);
>> +	if (ret < 0) {
>> +		free_extent_buffer(buf);
>> +		return ERR_PTR(ret);
>> +	}
>>  
>>  	btrfs_set_header_generation(buf, trans->transid);
>>  	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
>> -	btrfs_tree_lock(buf);
>>  	clean_tree_block(fs_info, buf);
>>  	clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
>>  
>> @@ -8721,7 +8726,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>  					       level - 1);
>>  		reada = 1;
>>  	}
>> -	btrfs_tree_lock(next);
>> +	ret = btrfs_tree_lock(next);
>> +	if (ret < 0)
>> +		goto out_free;
>>  	btrfs_set_lock_blocking(next);
>>  
>>  	ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
>> @@ -8781,7 +8788,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>  			free_extent_buffer(next);
>>  			return -EIO;
>>  		}
>> -		btrfs_tree_lock(next);
>> +		ret = btrfs_tree_lock(next);
>> +		if (ret < 0)
>> +			goto out_free;
>>  		btrfs_set_lock_blocking(next);
>>  	}
>>  
>> @@ -8839,6 +8848,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>  
>>  out_unlock:
>>  	btrfs_tree_unlock(next);
>> +out_free:
>>  	free_extent_buffer(next);
>>  
>>  	return ret;
>> @@ -8887,7 +8897,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>>  		 */
>>  		if (!path->locks[level]) {
>>  			BUG_ON(level == 0);
>> -			btrfs_tree_lock(eb);
>> +			ret = btrfs_tree_lock(eb);
>> +			BUG_ON(ret < 0);
>>  			btrfs_set_lock_blocking(eb);
>>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>>  
>> @@ -8929,7 +8940,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>>  		/* make block locked assertion in clean_tree_block happy */
>>  		if (!path->locks[level] &&
>>  		    btrfs_header_generation(eb) == trans->transid) {
>> -			btrfs_tree_lock(eb);
>> +			ret = btrfs_tree_lock(eb);
>> +			BUG_ON(ret < 0);
>>  			btrfs_set_lock_blocking(eb);
>>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>>  		}
>> @@ -9107,7 +9119,11 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
>>  
>>  		level = btrfs_header_level(root->node);
>>  		while (1) {
>> -			btrfs_tree_lock(path->nodes[level]);
>> +			ret = btrfs_tree_lock(path->nodes[level]);
>> +			if (ret < 0) {
>> +				err = ret;
>> +				goto out_end_trans;
>> +			}
>>  			btrfs_set_lock_blocking(path->nodes[level]);
>>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>>  
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index cce6087d6880..3ba02aac6dd5 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -3545,7 +3545,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>>  	if (!btrfs_try_tree_write_lock(eb)) {
>>  		flush = 1;
>>  		flush_write_bio(epd);
>> -		btrfs_tree_lock(eb);
>> +		ret = btrfs_tree_lock(eb);
>> +		if (ret < 0)
>> +			return ret;
>>  	}
>>  
>>  	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
>> @@ -3558,7 +3560,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>>  		}
>>  		while (1) {
>>  			wait_on_extent_buffer_writeback(eb);
>> -			btrfs_tree_lock(eb);
>> +			ret = btrfs_tree_lock(eb);
>> +			if (ret < 0)
>> +				return ret;
>>  			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>>  				break;
>>  			btrfs_tree_unlock(eb);
>> diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
>> index b5950aacd697..948bbc45638a 100644
>> --- a/fs/btrfs/free-space-tree.c
>> +++ b/fs/btrfs/free-space-tree.c
>> @@ -1242,7 +1242,9 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
>>  
>>  	list_del(&free_space_root->dirty_list);
>>  
>> -	btrfs_tree_lock(free_space_root->node);
>> +	ret = btrfs_tree_lock(free_space_root->node);
>> +	if (ret < 0)
>> +		goto abort;
>>  	clean_tree_block(fs_info, free_space_root->node);
>>  	btrfs_tree_unlock(free_space_root->node);
>>  	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
>> diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
>> index 1da768e5ef75..ca151be026bf 100644
>> --- a/fs/btrfs/locking.c
>> +++ b/fs/btrfs/locking.c
>> @@ -224,10 +224,18 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
>>  /*
>>   * take a spinning write lock.  This will wait for both
>>   * blocking readers or writers
>> + *
>> + * Return 0 if we successfully locked the tree block
>> + * Return <0 if some selftest failed (mostly due to extent tree corruption)
>>   */
>> -void btrfs_tree_lock(struct extent_buffer *eb)
>> +int btrfs_tree_lock(struct extent_buffer *eb)
>>  {
>> -	WARN_ON(eb->lock_owner == current->pid);
>> +	if (unlikely(eb->lock_owner == current->pid)) {
>> +		WARN(1,
>> +"tree block %llu already locked by current (pid=%d), refuse to lock",
>> +		     eb->start, current->pid);
>> +		return -EUCLEAN;
>> +	}
>>  again:
>>  	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
>>  	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
>> @@ -248,6 +256,7 @@ void btrfs_tree_lock(struct extent_buffer *eb)
>>  	atomic_inc(&eb->spinning_writers);
>>  	atomic_inc(&eb->write_locks);
>>  	eb->lock_owner = current->pid;
>> +	return 0;
>>  }
>>  
>>  /*
>> diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
>> index 29135def468e..7394d7ba2ff9 100644
>> --- a/fs/btrfs/locking.h
>> +++ b/fs/btrfs/locking.h
>> @@ -11,7 +11,7 @@
>>  #define BTRFS_WRITE_LOCK_BLOCKING 3
>>  #define BTRFS_READ_LOCK_BLOCKING 4
>>  
>> -void btrfs_tree_lock(struct extent_buffer *eb);
>> +int btrfs_tree_lock(struct extent_buffer *eb);
>>  void btrfs_tree_unlock(struct extent_buffer *eb);
>>  
>>  void btrfs_tree_read_lock(struct extent_buffer *eb);
>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>> index 1874a6d2e6f5..ec4351fd7537 100644
>> --- a/fs/btrfs/qgroup.c
>> +++ b/fs/btrfs/qgroup.c
>> @@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
>>  
>>  	list_del(&quota_root->dirty_list);
>>  
>> -	btrfs_tree_lock(quota_root->node);
>> +	ret = btrfs_tree_lock(quota_root->node);
>> +	if (ret < 0)
>> +		goto out;
>>  	clean_tree_block(fs_info, quota_root->node);
>>  	btrfs_tree_unlock(quota_root->node);
>>  	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
>> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
>> index be94c65bb4d2..a2fc0bd83a40 100644
>> --- a/fs/btrfs/relocation.c
>> +++ b/fs/btrfs/relocation.c
>> @@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
>>  				free_extent_buffer(eb);
>>  				break;
>>  			}
>> -			btrfs_tree_lock(eb);
>> +			ret = btrfs_tree_lock(eb);
>> +			if (ret < 0) {
>> +				free_extent_buffer(eb);
>> +				break;
>> +			}
>>  			if (cow) {
>>  				ret = btrfs_cow_block(trans, dest, eb, parent,
>>  						      slot, &eb);
>> @@ -2788,7 +2792,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
>>  			err = -EIO;
>>  			goto next;
>>  		}
>> -		btrfs_tree_lock(eb);
>> +		ret = btrfs_tree_lock(eb);
>> +		if (ret < 0) {
>> +			free_extent_buffer(eb);
>> +			err = ret;
>> +			goto next;
>> +		}
>>  		btrfs_set_lock_blocking(eb);
>>  
>>  		if (!node->eb) {
>> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
>> index f8220ec02036..173bc15a7cd1 100644
>> --- a/fs/btrfs/tree-log.c
>> +++ b/fs/btrfs/tree-log.c
>> @@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
>>  				}
>>  
>>  				if (trans) {
>> -					btrfs_tree_lock(next);
>> +					ret = btrfs_tree_lock(next);
>> +					if (ret < 0) {
>> +						free_extent_buffer(next);
>> +						return ret;
>> +					}
>>  					btrfs_set_lock_blocking(next);
>>  					clean_tree_block(fs_info, next);
>>  					btrfs_wait_tree_block_writeback(next);
>> @@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
>>  				next = path->nodes[*level];
>>  
>>  				if (trans) {
>> -					btrfs_tree_lock(next);
>> +					ret = btrfs_tree_lock(next);
>> +					if (ret < 0)
>> +						return ret;
>>  					btrfs_set_lock_blocking(next);
>>  					clean_tree_block(fs_info, next);
>>  					btrfs_wait_tree_block_writeback(next);
>> @@ -2754,7 +2760,9 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
>>  			next = path->nodes[orig_level];
>>  
>>  			if (trans) {
>> -				btrfs_tree_lock(next);
>> +				ret = btrfs_tree_lock(next);
>> +				if (ret < 0)
>> +					goto out;
>>  				btrfs_set_lock_blocking(next);
>>  				clean_tree_block(fs_info, next);
>>  				btrfs_wait_tree_block_writeback(next);
>> -- 
>> 2.18.0
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html


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Re: [PATCH v2] btrfs: locking: Allow btrfs_tree_lock() to return error to avoid deadlock

[Qu Wenruo]

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On 2018年08月01日 21:45, Qu Wenruo wrote:
> 
> 
> On 2018年08月01日 21:27, David Sterba wrote:
>> On Tue, Jul 31, 2018 at 02:52:23PM +0800, Qu Wenruo wrote:
>>> [BUG]
>>> For certains crafted image, whose csum root leaf has missing backref, if
>>> we try to trigger write with data csum, it could cause deadlock with the
>>> following kernel WARN_ON():
>>> ------
>>> WARNING: CPU: 1 PID: 41 at fs/btrfs/locking.c:230 btrfs_tree_lock+0x3e2/0x400
>>> CPU: 1 PID: 41 Comm: kworker/u4:1 Not tainted 4.18.0-rc1+ #8
>>> Workqueue: btrfs-endio-write btrfs_endio_write_helper
>>> RIP: 0010:btrfs_tree_lock+0x3e2/0x400
>>> Call Trace:
>>>  btrfs_alloc_tree_block+0x39f/0x770
>>>  __btrfs_cow_block+0x285/0x9e0
>>>  btrfs_cow_block+0x191/0x2e0
>>>  btrfs_search_slot+0x492/0x1160
>>>  btrfs_lookup_csum+0xec/0x280
>>>  btrfs_csum_file_blocks+0x2be/0xa60
>>>  add_pending_csums+0xaf/0xf0
>>>  btrfs_finish_ordered_io+0x74b/0xc90
>>>  finish_ordered_fn+0x15/0x20
>>>  normal_work_helper+0xf6/0x500
>>>  btrfs_endio_write_helper+0x12/0x20
>>>  process_one_work+0x302/0x770
>>>  worker_thread+0x81/0x6d0
>>>  kthread+0x180/0x1d0
>>>  ret_from_fork+0x35/0x40
>>> ---[ end trace 2e85051acb5f6dc1 ]---
>>> ------
>>>
>>> [CAUSE]
>>> That crafted image has missing backref for csum tree root leaf.
>>> And when we try to allocate new tree block, since there is no
>>> EXTENT/METADATA_ITEM for csum tree root, btrfs consider it's free slot
>>> and use it.
>>
>> I don't understand what exactly is the problem, can you please rephrase
>> that? Ie. what exactly is missing from where. If the problem is on the
>> higher level, regarding the csum tree, this could be checked much
>> earlier. I don't really like to see each and every callsite of tree
>> locks to require the error handling, so I'm exploring the possibilities
>> if this is necessary at all.
> 
> This is a little complex.
> 
> I'll try to explain this using some asciiart:
> 
> Normal image                      |       This fuzzed image
> ----------------------------------+--------------------------------
> BG 29360128                       | BG 29360128
>  One empty slot                   |  One empty slot
> 29364224: backref to UUID tree    | 29364224: backref to UUID tree
>  Two empty slots                  |  Two empty slots
> 29376512: backref to CSUM tree    |  One empty slot (bad type)
> 29380608: backref to D_RELOC tree | 29380608: backref to D_RELOC tree
> ...                               | ...
> 
> Since bytenr 29376512 has no METADATA/EXTENT_ITEM, when btrfs try to
> alloc tree block, it's an valid slot for btrfs.
> 
> And for finish_ordered_write, when we need to insert csum, we try to CoW
> csum tree root.
> 
> Then extent allocator gives a new extent bytenr 29376512 length 4096.
> However bytenr 29376512 is our current csum root, and already locked
> during CoW.
> 
> So in btrfs_alloc_tree_block() which calls btrfs_tree_lock() to lock the
> newly allocated tree block, we are trying to lock the tree block we have
> already locked, thus triggering the WARN_ON() and deadlock.

BTW, it's mostly a coincident that, btrfs tries to allocate the tree
block which is also current csum tree root.

For more common corruption case, we will hit some error when running
delayed refs and falls RO, other than hit this deadlock.

Thanks,
Qu

> 
> 
> In this particular fuzzed image, we can do key type check to detect
> early corruption, but it has the following problem:
> 
> 1) Won't really solve the problem
>    I could easily craft a image with backref for csum tree missing, and
>    everything else is OK. It will still cause the problem.
> 
> 2) May break later RO_compat features
>    If later RO_compat feature introduces new key type in extent tree, in
>    theory it should be able to be mounted RO, but will be rejected by
>    the type check.
> 
> So we have to go the way used in the patch.
> 
> Another solution would be do backref check each time we try to read out
> a tree block, but that's too costly and may screw up locking.
> 
> Thanks,
> Qu
> 
>>
>>> However we have already locked csum tree root leaf by ourselves, thus we
>>> will ourselves to release read/write lock, and causing deadlock.
>>>
>>> [FIX]
>>> This patch will allow btrfs_tree_lock() to return error number, so
>>> most callers can exit gracefully.
>>> (Some caller doesn't really expect btrfs_tree_lock() to return error,
>>> and in that case, we use BUG_ON())
>>>
>>> Since such problem can only happen in crafted image, we will still
>>> trigger kernel warning, but with a little more meaningful warning
>>> message.
>>>
>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=200405
>>> Reported-by: Xu Wen <wen.xu@gatech.edu>
>>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>>> Reviewed-by: Su Yue <suy.fnst@cn.fujitsu.com>
>>> ---
>>> changelog:
>>> v2:
>>>   Fix pid_t output format from %llu to %d. Pointed by Su.
>>>   Fix missing return 0 for btrfs_lock_tree().
>>>   Update reviewed-by tags.
>>> ---
>>>  fs/btrfs/ctree.c           | 57 +++++++++++++++++++++++++++++++-------
>>>  fs/btrfs/extent-tree.c     | 28 +++++++++++++++----
>>>  fs/btrfs/extent_io.c       |  8 ++++--
>>>  fs/btrfs/free-space-tree.c |  4 ++-
>>>  fs/btrfs/locking.c         | 13 +++++++--
>>>  fs/btrfs/locking.h         |  2 +-
>>>  fs/btrfs/qgroup.c          |  4 ++-
>>>  fs/btrfs/relocation.c      | 13 +++++++--
>>>  fs/btrfs/tree-log.c        | 14 ++++++++--
>>>  9 files changed, 115 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
>>> index 4bc326df472e..6e695f4cd931 100644
>>> --- a/fs/btrfs/ctree.c
>>> +++ b/fs/btrfs/ctree.c
>>> @@ -161,10 +161,12 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
>>>  struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
>>>  {
>>>  	struct extent_buffer *eb;
>>> +	int ret;
>>>  
>>>  	while (1) {
>>>  		eb = btrfs_root_node(root);
>>> -		btrfs_tree_lock(eb);
>>> +		ret = btrfs_tree_lock(eb);
>>> +		BUG_ON(ret < 0);
>>>  		if (eb == root->node)
>>>  			break;
>>>  		btrfs_tree_unlock(eb);
>>> @@ -1584,6 +1586,7 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>>>  	for (i = start_slot; i <= end_slot; i++) {
>>>  		struct btrfs_key first_key;
>>>  		int close = 1;
>>> +		int ret;
>>>  
>>>  		btrfs_node_key(parent, &disk_key, i);
>>>  		if (!progress_passed && comp_keys(&disk_key, progress) < 0)
>>> @@ -1637,7 +1640,11 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
>>>  		if (search_start == 0)
>>>  			search_start = last_block;
>>>  
>>> -		btrfs_tree_lock(cur);
>>> +		ret = btrfs_tree_lock(cur);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(cur);
>>> +			return ret;
>>> +		}
>>>  		btrfs_set_lock_blocking(cur);
>>>  		err = __btrfs_cow_block(trans, root, cur, parent, i,
>>>  					&cur, search_start,
>>> @@ -1853,7 +1860,11 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>>  			goto enospc;
>>>  		}
>>>  
>>> -		btrfs_tree_lock(child);
>>> +		ret = btrfs_tree_lock(child);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(child);
>>> +			goto enospc;
>>> +		}
>>>  		btrfs_set_lock_blocking(child);
>>>  		ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
>>>  		if (ret) {
>>> @@ -1891,7 +1902,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>>  		left = NULL;
>>>  
>>>  	if (left) {
>>> -		btrfs_tree_lock(left);
>>> +		ret = btrfs_tree_lock(left);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(left);
>>> +			left = NULL;
>>> +			goto enospc;
>>> +		}
>>>  		btrfs_set_lock_blocking(left);
>>>  		wret = btrfs_cow_block(trans, root, left,
>>>  				       parent, pslot - 1, &left);
>>> @@ -1906,7 +1922,12 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
>>>  		right = NULL;
>>>  
>>>  	if (right) {
>>> -		btrfs_tree_lock(right);
>>> +		ret = btrfs_tree_lock(right);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(right);
>>> +			right = NULL;
>>> +			goto enospc;
>>> +		}
>>>  		btrfs_set_lock_blocking(right);
>>>  		wret = btrfs_cow_block(trans, root, right,
>>>  				       parent, pslot + 1, &right);
>>> @@ -2069,7 +2090,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>>  	if (left) {
>>>  		u32 left_nr;
>>>  
>>> -		btrfs_tree_lock(left);
>>> +		ret = btrfs_tree_lock(left);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(left);
>>> +			return ret;
>>> +		}
>>>  		btrfs_set_lock_blocking(left);
>>>  
>>>  		left_nr = btrfs_header_nritems(left);
>>> @@ -2124,7 +2149,11 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
>>>  	if (right) {
>>>  		u32 right_nr;
>>>  
>>> -		btrfs_tree_lock(right);
>>> +		ret = btrfs_tree_lock(right);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(right);
>>> +			return ret;
>>> +		}
>>>  		btrfs_set_lock_blocking(right);
>>>  
>>>  		right_nr = btrfs_header_nritems(right);
>>> @@ -2874,7 +2903,9 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>>>  					err = btrfs_try_tree_write_lock(b);
>>>  					if (!err) {
>>>  						btrfs_set_path_blocking(p);
>>> -						btrfs_tree_lock(b);
>>> +						ret = btrfs_tree_lock(b);
>>> +						if (ret < 0)
>>> +							goto done;
>>>  						btrfs_clear_path_blocking(p, b,
>>>  								  BTRFS_WRITE_LOCK);
>>>  					}
>>> @@ -3773,7 +3804,9 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>>>  	if (IS_ERR(right))
>>>  		return 1;
>>>  
>>> -	btrfs_tree_lock(right);
>>> +	ret = btrfs_tree_lock(right);
>>> +	if (ret < 0)
>>> +		goto out_free;
>>>  	btrfs_set_lock_blocking(right);
>>>  
>>>  	free_space = btrfs_leaf_free_space(fs_info, right);
>>> @@ -3811,6 +3844,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
>>>  				right, free_space, left_nritems, min_slot);
>>>  out_unlock:
>>>  	btrfs_tree_unlock(right);
>>> +out_free:
>>>  	free_extent_buffer(right);
>>>  	return 1;
>>>  }
>>> @@ -4007,7 +4041,9 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>>>  	if (IS_ERR(left))
>>>  		return 1;
>>>  
>>> -	btrfs_tree_lock(left);
>>> +	ret = btrfs_tree_lock(left);
>>> +	if (ret < 0)
>>> +		goto out_free;
>>>  	btrfs_set_lock_blocking(left);
>>>  
>>>  	free_space = btrfs_leaf_free_space(fs_info, left);
>>> @@ -4037,6 +4073,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
>>>  			       max_slot);
>>>  out:
>>>  	btrfs_tree_unlock(left);
>>> +out_free:
>>>  	free_extent_buffer(left);
>>>  	return ret;
>>>  }
>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>> index 3578fa5b30ef..da615ebc072e 100644
>>> --- a/fs/btrfs/extent-tree.c
>>> +++ b/fs/btrfs/extent-tree.c
>>> @@ -8297,14 +8297,19 @@ btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
>>>  {
>>>  	struct btrfs_fs_info *fs_info = root->fs_info;
>>>  	struct extent_buffer *buf;
>>> +	int ret;
>>>  
>>>  	buf = btrfs_find_create_tree_block(fs_info, bytenr);
>>>  	if (IS_ERR(buf))
>>>  		return buf;
>>> +	ret = btrfs_tree_lock(buf);
>>> +	if (ret < 0) {
>>> +		free_extent_buffer(buf);
>>> +		return ERR_PTR(ret);
>>> +	}
>>>  
>>>  	btrfs_set_header_generation(buf, trans->transid);
>>>  	btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
>>> -	btrfs_tree_lock(buf);
>>>  	clean_tree_block(fs_info, buf);
>>>  	clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);
>>>  
>>> @@ -8721,7 +8726,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>>  					       level - 1);
>>>  		reada = 1;
>>>  	}
>>> -	btrfs_tree_lock(next);
>>> +	ret = btrfs_tree_lock(next);
>>> +	if (ret < 0)
>>> +		goto out_free;
>>>  	btrfs_set_lock_blocking(next);
>>>  
>>>  	ret = btrfs_lookup_extent_info(trans, fs_info, bytenr, level - 1, 1,
>>> @@ -8781,7 +8788,9 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>>  			free_extent_buffer(next);
>>>  			return -EIO;
>>>  		}
>>> -		btrfs_tree_lock(next);
>>> +		ret = btrfs_tree_lock(next);
>>> +		if (ret < 0)
>>> +			goto out_free;
>>>  		btrfs_set_lock_blocking(next);
>>>  	}
>>>  
>>> @@ -8839,6 +8848,7 @@ static noinline int do_walk_down(struct btrfs_trans_handle *trans,
>>>  
>>>  out_unlock:
>>>  	btrfs_tree_unlock(next);
>>> +out_free:
>>>  	free_extent_buffer(next);
>>>  
>>>  	return ret;
>>> @@ -8887,7 +8897,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>>>  		 */
>>>  		if (!path->locks[level]) {
>>>  			BUG_ON(level == 0);
>>> -			btrfs_tree_lock(eb);
>>> +			ret = btrfs_tree_lock(eb);
>>> +			BUG_ON(ret < 0);
>>>  			btrfs_set_lock_blocking(eb);
>>>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>>>  
>>> @@ -8929,7 +8940,8 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
>>>  		/* make block locked assertion in clean_tree_block happy */
>>>  		if (!path->locks[level] &&
>>>  		    btrfs_header_generation(eb) == trans->transid) {
>>> -			btrfs_tree_lock(eb);
>>> +			ret = btrfs_tree_lock(eb);
>>> +			BUG_ON(ret < 0);
>>>  			btrfs_set_lock_blocking(eb);
>>>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>>>  		}
>>> @@ -9107,7 +9119,11 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
>>>  
>>>  		level = btrfs_header_level(root->node);
>>>  		while (1) {
>>> -			btrfs_tree_lock(path->nodes[level]);
>>> +			ret = btrfs_tree_lock(path->nodes[level]);
>>> +			if (ret < 0) {
>>> +				err = ret;
>>> +				goto out_end_trans;
>>> +			}
>>>  			btrfs_set_lock_blocking(path->nodes[level]);
>>>  			path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
>>>  
>>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>>> index cce6087d6880..3ba02aac6dd5 100644
>>> --- a/fs/btrfs/extent_io.c
>>> +++ b/fs/btrfs/extent_io.c
>>> @@ -3545,7 +3545,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>>>  	if (!btrfs_try_tree_write_lock(eb)) {
>>>  		flush = 1;
>>>  		flush_write_bio(epd);
>>> -		btrfs_tree_lock(eb);
>>> +		ret = btrfs_tree_lock(eb);
>>> +		if (ret < 0)
>>> +			return ret;
>>>  	}
>>>  
>>>  	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
>>> @@ -3558,7 +3560,9 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
>>>  		}
>>>  		while (1) {
>>>  			wait_on_extent_buffer_writeback(eb);
>>> -			btrfs_tree_lock(eb);
>>> +			ret = btrfs_tree_lock(eb);
>>> +			if (ret < 0)
>>> +				return ret;
>>>  			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
>>>  				break;
>>>  			btrfs_tree_unlock(eb);
>>> diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
>>> index b5950aacd697..948bbc45638a 100644
>>> --- a/fs/btrfs/free-space-tree.c
>>> +++ b/fs/btrfs/free-space-tree.c
>>> @@ -1242,7 +1242,9 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
>>>  
>>>  	list_del(&free_space_root->dirty_list);
>>>  
>>> -	btrfs_tree_lock(free_space_root->node);
>>> +	ret = btrfs_tree_lock(free_space_root->node);
>>> +	if (ret < 0)
>>> +		goto abort;
>>>  	clean_tree_block(fs_info, free_space_root->node);
>>>  	btrfs_tree_unlock(free_space_root->node);
>>>  	btrfs_free_tree_block(trans, free_space_root, free_space_root->node,
>>> diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
>>> index 1da768e5ef75..ca151be026bf 100644
>>> --- a/fs/btrfs/locking.c
>>> +++ b/fs/btrfs/locking.c
>>> @@ -224,10 +224,18 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
>>>  /*
>>>   * take a spinning write lock.  This will wait for both
>>>   * blocking readers or writers
>>> + *
>>> + * Return 0 if we successfully locked the tree block
>>> + * Return <0 if some selftest failed (mostly due to extent tree corruption)
>>>   */
>>> -void btrfs_tree_lock(struct extent_buffer *eb)
>>> +int btrfs_tree_lock(struct extent_buffer *eb)
>>>  {
>>> -	WARN_ON(eb->lock_owner == current->pid);
>>> +	if (unlikely(eb->lock_owner == current->pid)) {
>>> +		WARN(1,
>>> +"tree block %llu already locked by current (pid=%d), refuse to lock",
>>> +		     eb->start, current->pid);
>>> +		return -EUCLEAN;
>>> +	}
>>>  again:
>>>  	wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
>>>  	wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
>>> @@ -248,6 +256,7 @@ void btrfs_tree_lock(struct extent_buffer *eb)
>>>  	atomic_inc(&eb->spinning_writers);
>>>  	atomic_inc(&eb->write_locks);
>>>  	eb->lock_owner = current->pid;
>>> +	return 0;
>>>  }
>>>  
>>>  /*
>>> diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h
>>> index 29135def468e..7394d7ba2ff9 100644
>>> --- a/fs/btrfs/locking.h
>>> +++ b/fs/btrfs/locking.h
>>> @@ -11,7 +11,7 @@
>>>  #define BTRFS_WRITE_LOCK_BLOCKING 3
>>>  #define BTRFS_READ_LOCK_BLOCKING 4
>>>  
>>> -void btrfs_tree_lock(struct extent_buffer *eb);
>>> +int btrfs_tree_lock(struct extent_buffer *eb);
>>>  void btrfs_tree_unlock(struct extent_buffer *eb);
>>>  
>>>  void btrfs_tree_read_lock(struct extent_buffer *eb);
>>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>>> index 1874a6d2e6f5..ec4351fd7537 100644
>>> --- a/fs/btrfs/qgroup.c
>>> +++ b/fs/btrfs/qgroup.c
>>> @@ -1040,7 +1040,9 @@ int btrfs_quota_disable(struct btrfs_trans_handle *trans,
>>>  
>>>  	list_del(&quota_root->dirty_list);
>>>  
>>> -	btrfs_tree_lock(quota_root->node);
>>> +	ret = btrfs_tree_lock(quota_root->node);
>>> +	if (ret < 0)
>>> +		goto out;
>>>  	clean_tree_block(fs_info, quota_root->node);
>>>  	btrfs_tree_unlock(quota_root->node);
>>>  	btrfs_free_tree_block(trans, quota_root, quota_root->node, 0, 1);
>>> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
>>> index be94c65bb4d2..a2fc0bd83a40 100644
>>> --- a/fs/btrfs/relocation.c
>>> +++ b/fs/btrfs/relocation.c
>>> @@ -1877,7 +1877,11 @@ int replace_path(struct btrfs_trans_handle *trans,
>>>  				free_extent_buffer(eb);
>>>  				break;
>>>  			}
>>> -			btrfs_tree_lock(eb);
>>> +			ret = btrfs_tree_lock(eb);
>>> +			if (ret < 0) {
>>> +				free_extent_buffer(eb);
>>> +				break;
>>> +			}
>>>  			if (cow) {
>>>  				ret = btrfs_cow_block(trans, dest, eb, parent,
>>>  						      slot, &eb);
>>> @@ -2788,7 +2792,12 @@ static int do_relocation(struct btrfs_trans_handle *trans,
>>>  			err = -EIO;
>>>  			goto next;
>>>  		}
>>> -		btrfs_tree_lock(eb);
>>> +		ret = btrfs_tree_lock(eb);
>>> +		if (ret < 0) {
>>> +			free_extent_buffer(eb);
>>> +			err = ret;
>>> +			goto next;
>>> +		}
>>>  		btrfs_set_lock_blocking(eb);
>>>  
>>>  		if (!node->eb) {
>>> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
>>> index f8220ec02036..173bc15a7cd1 100644
>>> --- a/fs/btrfs/tree-log.c
>>> +++ b/fs/btrfs/tree-log.c
>>> @@ -2588,7 +2588,11 @@ static noinline int walk_down_log_tree(struct btrfs_trans_handle *trans,
>>>  				}
>>>  
>>>  				if (trans) {
>>> -					btrfs_tree_lock(next);
>>> +					ret = btrfs_tree_lock(next);
>>> +					if (ret < 0) {
>>> +						free_extent_buffer(next);
>>> +						return ret;
>>> +					}
>>>  					btrfs_set_lock_blocking(next);
>>>  					clean_tree_block(fs_info, next);
>>>  					btrfs_wait_tree_block_writeback(next);
>>> @@ -2672,7 +2676,9 @@ static noinline int walk_up_log_tree(struct btrfs_trans_handle *trans,
>>>  				next = path->nodes[*level];
>>>  
>>>  				if (trans) {
>>> -					btrfs_tree_lock(next);
>>> +					ret = btrfs_tree_lock(next);
>>> +					if (ret < 0)
>>> +						return ret;
>>>  					btrfs_set_lock_blocking(next);
>>>  					clean_tree_block(fs_info, next);
>>>  					btrfs_wait_tree_block_writeback(next);
>>> @@ -2754,7 +2760,9 @@ static int walk_log_tree(struct btrfs_trans_handle *trans,
>>>  			next = path->nodes[orig_level];
>>>  
>>>  			if (trans) {
>>> -				btrfs_tree_lock(next);
>>> +				ret = btrfs_tree_lock(next);
>>> +				if (ret < 0)
>>> +					goto out;
>>>  				btrfs_set_lock_blocking(next);
>>>  				clean_tree_block(fs_info, next);
>>>  				btrfs_wait_tree_block_writeback(next);
>>> -- 
>>> 2.18.0
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


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