[PATCH] btrfs: fix deadlock when cloning inline extents and using qgroups

* [PATCH] btrfs: fix deadlock when cloning inline extents and using qgroups
@ 2021-04-22 11:08 fdmanana
  2021-04-22 11:16 ` Qu Wenruo
  2021-04-28 18:08 ` David Sterba
  0 siblings, 2 replies; 3+ messages in thread
From: fdmanana @ 2021-04-22 11:08 UTC (permalink / raw)
  To: linux-btrfs

From: Filipe Manana <fdmanana@suse.com>

There are a few exceptional cases where cloning an inline extent needs to
copy the inline extent data into a page of the destination inode.

When this happens, we end up starting a transaction while having a dirty
page for the destination inode and while having the range locked in the
destination's inode iotree too. Because when reserving metadata space
for a transaction we may need to flush existing delalloc in case there is
not enough free space, we have a mechanism in place to prevent a deadlock,
which was introduced in commit 3d45f221ce627d ("btrfs: fix deadlock when
cloning inline extent and low on free metadata space").

However when using qgroups, a transaction also reserves metadata qgroup
space, which can also result in flushing delalloc in case there is not
enough available space at the moment. When this happens we deadlock, since
flushing delalloc requires locking the file range in the inode's iotree
and the range was already locked at the very beginning of the clone
operation, before attempting to start the transaction.

When this issue happens, stack traces like the following are reported:

[72747.556262] task:kworker/u81:9   state:D stack:    0 pid:  225 ppid:     2 flags:0x00004000
[72747.556268] Workqueue: writeback wb_workfn (flush-btrfs-1142)
[72747.556271] Call Trace:
[72747.556273]  __schedule+0x296/0x760
[72747.556277]  schedule+0x3c/0xa0
[72747.556279]  io_schedule+0x12/0x40
[72747.556284]  __lock_page+0x13c/0x280
[72747.556287]  ? generic_file_readonly_mmap+0x70/0x70
[72747.556325]  extent_write_cache_pages+0x22a/0x440 [btrfs]
[72747.556331]  ? __set_page_dirty_nobuffers+0xe7/0x160
[72747.556358]  ? set_extent_buffer_dirty+0x5e/0x80 [btrfs]
[72747.556362]  ? update_group_capacity+0x25/0x210
[72747.556366]  ? cpumask_next_and+0x1a/0x20
[72747.556391]  extent_writepages+0x44/0xa0 [btrfs]
[72747.556394]  do_writepages+0x41/0xd0
[72747.556398]  __writeback_single_inode+0x39/0x2a0
[72747.556403]  writeback_sb_inodes+0x1ea/0x440
[72747.556407]  __writeback_inodes_wb+0x5f/0xc0
[72747.556410]  wb_writeback+0x235/0x2b0
[72747.556414]  ? get_nr_inodes+0x35/0x50
[72747.556417]  wb_workfn+0x354/0x490
[72747.556420]  ? newidle_balance+0x2c5/0x3e0
[72747.556424]  process_one_work+0x1aa/0x340
[72747.556426]  worker_thread+0x30/0x390
[72747.556429]  ? create_worker+0x1a0/0x1a0
[72747.556432]  kthread+0x116/0x130
[72747.556435]  ? kthread_park+0x80/0x80
[72747.556438]  ret_from_fork+0x1f/0x30

[72747.566958] Workqueue: btrfs-flush_delalloc btrfs_work_helper [btrfs]
[72747.566961] Call Trace:
[72747.566964]  __schedule+0x296/0x760
[72747.566968]  ? finish_wait+0x80/0x80
[72747.566970]  schedule+0x3c/0xa0
[72747.566995]  wait_extent_bit.constprop.68+0x13b/0x1c0 [btrfs]
[72747.566999]  ? finish_wait+0x80/0x80
[72747.567024]  lock_extent_bits+0x37/0x90 [btrfs]
[72747.567047]  btrfs_invalidatepage+0x299/0x2c0 [btrfs]
[72747.567051]  ? find_get_pages_range_tag+0x2cd/0x380
[72747.567076]  __extent_writepage+0x203/0x320 [btrfs]
[72747.567102]  extent_write_cache_pages+0x2bb/0x440 [btrfs]
[72747.567106]  ? update_load_avg+0x7e/0x5f0
[72747.567109]  ? enqueue_entity+0xf4/0x6f0
[72747.567134]  extent_writepages+0x44/0xa0 [btrfs]
[72747.567137]  ? enqueue_task_fair+0x93/0x6f0
[72747.567140]  do_writepages+0x41/0xd0
[72747.567144]  __filemap_fdatawrite_range+0xc7/0x100
[72747.567167]  btrfs_run_delalloc_work+0x17/0x40 [btrfs]
[72747.567195]  btrfs_work_helper+0xc2/0x300 [btrfs]
[72747.567200]  process_one_work+0x1aa/0x340
[72747.567202]  worker_thread+0x30/0x390
[72747.567205]  ? create_worker+0x1a0/0x1a0
[72747.567208]  kthread+0x116/0x130
[72747.567211]  ? kthread_park+0x80/0x80
[72747.567214]  ret_from_fork+0x1f/0x30

[72747.569686] task:fsstress        state:D stack:    0 pid:841421 ppid:841417 flags:0x00000000
[72747.569689] Call Trace:
[72747.569691]  __schedule+0x296/0x760
[72747.569694]  schedule+0x3c/0xa0
[72747.569721]  try_flush_qgroup+0x95/0x140 [btrfs]
[72747.569725]  ? finish_wait+0x80/0x80
[72747.569753]  btrfs_qgroup_reserve_data+0x34/0x50 [btrfs]
[72747.569781]  btrfs_check_data_free_space+0x5f/0xa0 [btrfs]
[72747.569804]  btrfs_buffered_write+0x1f7/0x7f0 [btrfs]
[72747.569810]  ? path_lookupat.isra.48+0x97/0x140
[72747.569833]  btrfs_file_write_iter+0x81/0x410 [btrfs]
[72747.569836]  ? __kmalloc+0x16a/0x2c0
[72747.569839]  do_iter_readv_writev+0x160/0x1c0
[72747.569843]  do_iter_write+0x80/0x1b0
[72747.569847]  vfs_writev+0x84/0x140
[72747.569869]  ? btrfs_file_llseek+0x38/0x270 [btrfs]
[72747.569873]  do_writev+0x65/0x100
[72747.569876]  do_syscall_64+0x33/0x40
[72747.569879]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

[72747.569899] task:fsstress        state:D stack:    0 pid:841424 ppid:841417 flags:0x00004000
[72747.569903] Call Trace:
[72747.569906]  __schedule+0x296/0x760
[72747.569909]  schedule+0x3c/0xa0
[72747.569936]  try_flush_qgroup+0x95/0x140 [btrfs]
[72747.569940]  ? finish_wait+0x80/0x80
[72747.569967]  __btrfs_qgroup_reserve_meta+0x36/0x50 [btrfs]
[72747.569989]  start_transaction+0x279/0x580 [btrfs]
[72747.570014]  clone_copy_inline_extent+0x332/0x490 [btrfs]
[72747.570041]  btrfs_clone+0x5b7/0x7a0 [btrfs]
[72747.570068]  ? lock_extent_bits+0x64/0x90 [btrfs]
[72747.570095]  btrfs_clone_files+0xfc/0x150 [btrfs]
[72747.570122]  btrfs_remap_file_range+0x3d8/0x4a0 [btrfs]
[72747.570126]  do_clone_file_range+0xed/0x200
[72747.570131]  vfs_clone_file_range+0x37/0x110
[72747.570134]  ioctl_file_clone+0x7d/0xb0
[72747.570137]  do_vfs_ioctl+0x138/0x630
[72747.570140]  __x64_sys_ioctl+0x62/0xc0
[72747.570143]  do_syscall_64+0x33/0x40
[72747.570146]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

So fix this by skipping the flush of delalloc for an inode that is
flagged with BTRFS_INODE_NO_DELALLOC_FLUSH, meaning it is currently under
such a special case of cloning an inline extent, when flushing delalloc
during qgroup metadata reservation.

The special cases for cloning inline extents were added in kernel 5.7 by
by commit 05a5a7621ce66c ("Btrfs: implement full reflink support for
inline extents"), while having qgroup metadata space reservation flushing
delalloc when low on space was added in kernel 5.9 by commit
c53e9653605dbf ("btrfs: qgroup: try to flush qgroup space when we get
-EDQUOT"). So use a "Fixes:" tag for the later commit to ease stable
kernel backports.

Reported-by: Wang Yugui <wangyugui@e16-tech.com>
Link: https://lore.kernel.org/linux-btrfs/20210421083137.31E3.409509F4@e16-tech.com/
Fixes: c53e9653605dbf ("btrfs: qgroup: try to flush qgroup space when we get -EDQUOT")
CC: stable@vger.kernel.org # 5.9+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/ctree.h  | 3 ++-
 fs/btrfs/inode.c  | 5 +++--
 fs/btrfs/ioctl.c  | 2 +-
 fs/btrfs/qgroup.c | 2 +-
 fs/btrfs/send.c   | 4 ++--
 5 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 278e0cbc9a98..1807e7a8d1d7 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3127,7 +3127,8 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 			       struct btrfs_inode *inode, u64 new_size,
 			       u32 min_type);
 
-int btrfs_start_delalloc_snapshot(struct btrfs_root *root);
+int btrfs_start_delalloc_snapshot(struct btrfs_root *root,
+				  bool in_reclaim_context);
 int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, long nr,
 			       bool in_reclaim_context);
 int btrfs_set_extent_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1a349759efae..23854d180e94 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9691,7 +9691,8 @@ static int start_delalloc_inodes(struct btrfs_root *root,
 	return ret;
 }
 
-int btrfs_start_delalloc_snapshot(struct btrfs_root *root)
+int btrfs_start_delalloc_snapshot(struct btrfs_root *root,
+				  bool in_reclaim_context)
 {
 	struct writeback_control wbc = {
 		.nr_to_write = LONG_MAX,
@@ -9704,7 +9705,7 @@ int btrfs_start_delalloc_snapshot(struct btrfs_root *root)
 	if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state))
 		return -EROFS;
 
-	return start_delalloc_inodes(root, &wbc, true, false);
+	return start_delalloc_inodes(root, &wbc, true, in_reclaim_context);
 }
 
 int btrfs_start_delalloc_roots(struct btrfs_fs_info *fs_info, long nr,
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index b1328f17607e..0ba0e4ddaf6b 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1051,7 +1051,7 @@ static noinline int btrfs_mksnapshot(const struct path *parent,
 	 */
 	btrfs_drew_read_lock(&root->snapshot_lock);
 
-	ret = btrfs_start_delalloc_snapshot(root);
+	ret = btrfs_start_delalloc_snapshot(root, false);
 	if (ret)
 		goto out;
 
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 2319c923c9e6..366a6a289796 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3562,7 +3562,7 @@ static int try_flush_qgroup(struct btrfs_root *root)
 		return 0;
 	}
 
-	ret = btrfs_start_delalloc_snapshot(root);
+	ret = btrfs_start_delalloc_snapshot(root, true);
 	if (ret < 0)
 		goto out;
 	btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 55741adf9071..bd69db72acc5 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -7170,7 +7170,7 @@ static int flush_delalloc_roots(struct send_ctx *sctx)
 	int i;
 
 	if (root) {
-		ret = btrfs_start_delalloc_snapshot(root);
+		ret = btrfs_start_delalloc_snapshot(root, false);
 		if (ret)
 			return ret;
 		btrfs_wait_ordered_extents(root, U64_MAX, 0, U64_MAX);
@@ -7178,7 +7178,7 @@ static int flush_delalloc_roots(struct send_ctx *sctx)
 
 	for (i = 0; i < sctx->clone_roots_cnt; i++) {
 		root = sctx->clone_roots[i].root;
-		ret = btrfs_start_delalloc_snapshot(root);
+		ret = btrfs_start_delalloc_snapshot(root, false);
 		if (ret)
 			return ret;
 		btrfs_wait_ordered_extents(root, U64_MAX, 0, U64_MAX);
-- 
2.28.0


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