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From: Boris Burkov <boris@bur.io>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH v7 12/12] btrfs: fix lockdep error creating free space tree
Date: Wed, 18 Nov 2020 15:06:27 -0800	[thread overview]
Message-ID: <1dc72f7e64535cda2fbc798e1130d4b516197136.1605736355.git.boris@bur.io> (raw)
In-Reply-To: <cover.1605736355.git.boris@bur.io>

A lock dependency loop exists between the root tree lock, the extent tree
lock, and the free space tree lock.

The root tree lock depends on the free space tree lock because
btrfs_create_tree holds the new tree's lock while adding it to the root
tree.

The extent tree lock depends on the root tree lock because during umount,
we write out space cache v1, which writes inodes in the root tree, which
results in holding the root tree lock while doing a lookup in the extent tree.

Finally, the free space tree depends on the extent tree because
populate_free_space_tree holds a locked path in the extent tree and then
does a lookup in the free space tree to add the new item.

The simplest of the three to break is the one during tree creation: we
unlock the leaf before inserting the tree node into the root tree, which
fixes the lockdep.

Full contents of lockdep error for reference:

[   30.480136] ======================================================
[   30.480830] WARNING: possible circular locking dependency detected
[   30.481457] 5.9.0-rc8+ #76 Not tainted
[   30.481897] ------------------------------------------------------
[   30.482500] mount/520 is trying to acquire lock:
[   30.483064] ffff9babebe03908 (btrfs-free-space-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180
[   30.484054]
               but task is already holding lock:
[   30.484637] ffff9babebe24468 (btrfs-extent-01#2){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180
[   30.485581]
               which lock already depends on the new lock.

[   30.486397]
               the existing dependency chain (in reverse order) is:
[   30.487205]
               -> #2 (btrfs-extent-01#2){++++}-{3:3}:
[   30.487825]        down_read_nested+0x43/0x150
[   30.488306]        __btrfs_tree_read_lock+0x39/0x180
[   30.488868]        __btrfs_read_lock_root_node+0x3a/0x50
[   30.489477]        btrfs_search_slot+0x464/0x9b0
[   30.490009]        check_committed_ref+0x59/0x1d0
[   30.490603]        btrfs_cross_ref_exist+0x65/0xb0
[   30.491108]        run_delalloc_nocow+0x405/0x930
[   30.491651]        btrfs_run_delalloc_range+0x60/0x6b0
[   30.492203]        writepage_delalloc+0xd4/0x150
[   30.492688]        __extent_writepage+0x18d/0x3a0
[   30.493199]        extent_write_cache_pages+0x2af/0x450
[   30.493743]        extent_writepages+0x34/0x70
[   30.494231]        do_writepages+0x31/0xd0
[   30.494642]        __filemap_fdatawrite_range+0xad/0xe0
[   30.495194]        btrfs_fdatawrite_range+0x1b/0x50
[   30.495677]        __btrfs_write_out_cache+0x40d/0x460
[   30.496227]        btrfs_write_out_cache+0x8b/0x110
[   30.496716]        btrfs_start_dirty_block_groups+0x211/0x4e0
[   30.497317]        btrfs_commit_transaction+0xc0/0xba0
[   30.497861]        sync_filesystem+0x71/0x90
[   30.498303]        btrfs_remount+0x81/0x433
[   30.498767]        reconfigure_super+0x9f/0x210
[   30.499261]        path_mount+0x9d1/0xa30
[   30.499722]        do_mount+0x55/0x70
[   30.500158]        __x64_sys_mount+0xc4/0xe0
[   30.500616]        do_syscall_64+0x33/0x40
[   30.501091]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   30.501629]
               -> #1 (btrfs-root-00){++++}-{3:3}:
[   30.502241]        down_read_nested+0x43/0x150
[   30.502727]        __btrfs_tree_read_lock+0x39/0x180
[   30.503291]        __btrfs_read_lock_root_node+0x3a/0x50
[   30.503903]        btrfs_search_slot+0x464/0x9b0
[   30.504405]        btrfs_insert_empty_items+0x60/0xa0
[   30.504973]        btrfs_insert_item+0x60/0xd0
[   30.505412]        btrfs_create_tree+0x1b6/0x210
[   30.505913]        btrfs_create_free_space_tree+0x54/0x110
[   30.506460]        btrfs_mount_rw+0x15d/0x20f
[   30.506937]        btrfs_remount+0x356/0x433
[   30.507369]        reconfigure_super+0x9f/0x210
[   30.507868]        path_mount+0x9d1/0xa30
[   30.508264]        do_mount+0x55/0x70
[   30.508668]        __x64_sys_mount+0xc4/0xe0
[   30.509186]        do_syscall_64+0x33/0x40
[   30.509652]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   30.510271]
               -> #0 (btrfs-free-space-00){++++}-{3:3}:
[   30.510972]        __lock_acquire+0x11ad/0x1b60
[   30.511432]        lock_acquire+0xa2/0x360
[   30.511917]        down_read_nested+0x43/0x150
[   30.512383]        __btrfs_tree_read_lock+0x39/0x180
[   30.512947]        __btrfs_read_lock_root_node+0x3a/0x50
[   30.513455]        btrfs_search_slot+0x464/0x9b0
[   30.513947]        search_free_space_info+0x45/0x90
[   30.514465]        __add_to_free_space_tree+0x92/0x39d
[   30.515010]        btrfs_create_free_space_tree.cold.22+0x1ee/0x45d
[   30.515639]        btrfs_mount_rw+0x15d/0x20f
[   30.516142]        btrfs_remount+0x356/0x433
[   30.516538]        reconfigure_super+0x9f/0x210
[   30.517065]        path_mount+0x9d1/0xa30
[   30.517438]        do_mount+0x55/0x70
[   30.517824]        __x64_sys_mount+0xc4/0xe0
[   30.518293]        do_syscall_64+0x33/0x40
[   30.518776]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   30.519335]
               other info that might help us debug this:

[   30.520210] Chain exists of:
                 btrfs-free-space-00 --> btrfs-root-00 --> btrfs-extent-01#2

[   30.521407]  Possible unsafe locking scenario:

[   30.522037]        CPU0                    CPU1
[   30.522456]        ----                    ----
[   30.522941]   lock(btrfs-extent-01#2);
[   30.523311]                                lock(btrfs-root-00);
[   30.523952]                                lock(btrfs-extent-01#2);
[   30.524620]   lock(btrfs-free-space-00);
[   30.525068]
                *** DEADLOCK ***

[   30.525669] 5 locks held by mount/520:
[   30.526116]  #0: ffff9babebc520e0 (&type->s_umount_key#37){+.+.}-{3:3}, at: path_mount+0x7ef/0xa30
[   30.527056]  #1: ffff9babebc52640 (sb_internal#2){.+.+}-{0:0}, at: start_transaction+0x3d5/0x5c0
[   30.527960]  #2: ffff9babeae8f2e8 (&cache->free_space_lock#2){+.+.}-{3:3}, at: btrfs_create_free_space_tree.cold.22+0x101/0x45d
[   30.529118]  #3: ffff9babebe24468 (btrfs-extent-01#2){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180
[   30.530113]  #4: ffff9babebd52eb8 (btrfs-extent-00){++++}-{3:3}, at: btrfs_try_tree_read_lock+0x16/0x100
[   30.531124]
               stack backtrace:
[   30.531528] CPU: 0 PID: 520 Comm: mount Not tainted 5.9.0-rc8+ #76
[   30.532166] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-4.module_el8.1.0+248+298dec18 04/01/2014
[   30.533215] Call Trace:
[   30.533452]  dump_stack+0x8d/0xc0
[   30.533797]  check_noncircular+0x13c/0x150
[   30.534233]  __lock_acquire+0x11ad/0x1b60
[   30.534667]  lock_acquire+0xa2/0x360
[   30.535063]  ? __btrfs_tree_read_lock+0x39/0x180
[   30.535525]  down_read_nested+0x43/0x150
[   30.535939]  ? __btrfs_tree_read_lock+0x39/0x180
[   30.536400]  __btrfs_tree_read_lock+0x39/0x180
[   30.536862]  __btrfs_read_lock_root_node+0x3a/0x50
[   30.537304]  btrfs_search_slot+0x464/0x9b0
[   30.537713]  ? trace_hardirqs_on+0x1c/0xf0
[   30.538148]  search_free_space_info+0x45/0x90
[   30.538572]  __add_to_free_space_tree+0x92/0x39d
[   30.539071]  ? printk+0x48/0x4a
[   30.539367]  btrfs_create_free_space_tree.cold.22+0x1ee/0x45d
[   30.539972]  btrfs_mount_rw+0x15d/0x20f
[   30.540350]  btrfs_remount+0x356/0x433
[   30.540773]  ? shrink_dcache_sb+0xd9/0x100
[   30.541203]  reconfigure_super+0x9f/0x210
[   30.541642]  path_mount+0x9d1/0xa30
[   30.542040]  do_mount+0x55/0x70
[   30.542366]  __x64_sys_mount+0xc4/0xe0
[   30.542822]  do_syscall_64+0x33/0x40
[   30.543197]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   30.543691] RIP: 0033:0x7f109f7ab93a
[   30.544053] Code: 48 8b 0d 49 e5 0b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 16 e5 0b 00 f7 d8 64 89 01 48
[   30.546042] RSP: 002b:00007ffc47c4f858 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
[   30.546770] RAX: ffffffffffffffda RBX: 00007f109f8cf264 RCX: 00007f109f7ab93a
[   30.547485] RDX: 0000557e6fc10770 RSI: 0000557e6fc19cf0 RDI: 0000557e6fc19cd0
[   30.548185] RBP: 0000557e6fc10520 R08: 0000557e6fc18e30 R09: 0000557e6fc18cb0
[   30.548911] R10: 0000000000200020 R11: 0000000000000246 R12: 0000000000000000
[   30.549606] R13: 0000557e6fc19cd0 R14: 0000557e6fc10770 R15: 0000557e6fc10520

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/disk-io.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index fea467c421e7..1934bf6a99da 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1142,7 +1142,7 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 	if (IS_ERR(leaf)) {
 		ret = PTR_ERR(leaf);
 		leaf = NULL;
-		goto fail;
+		goto fail_unlock;
 	}
 
 	root->node = leaf;
@@ -1166,6 +1166,8 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 		export_guid(root->root_item.uuid, &guid_null);
 	btrfs_set_root_drop_level(&root->root_item, 0);
 
+	btrfs_tree_unlock(leaf);
+
 	key.objectid = objectid;
 	key.type = BTRFS_ROOT_ITEM_KEY;
 	key.offset = 0;
@@ -1173,13 +1175,12 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 	if (ret)
 		goto fail;
 
-	btrfs_tree_unlock(leaf);
-
 	return root;
 
-fail:
+fail_unlock:
 	if (leaf)
 		btrfs_tree_unlock(leaf);
+fail:
 	btrfs_put_root(root);
 
 	return ERR_PTR(ret);
-- 
2.24.1


  parent reply	other threads:[~2020-11-18 23:07 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-18 23:06 [PATCH v7 00/10] btrfs: free space tree mounting fixes Boris Burkov
2020-11-18 23:06 ` [PATCH v7 01/12] btrfs: lift rw mount setup from mount and remount Boris Burkov
2020-11-23 16:50   ` David Sterba
2020-11-30 23:31     ` Boris Burkov
2020-12-15 18:01       ` David Sterba
2020-11-23 16:57   ` David Sterba
2020-12-01  0:01     ` Boris Burkov
2020-12-15 17:50       ` David Sterba
2020-11-18 23:06 ` [PATCH v7 02/12] btrfs: cleanup all orphan inodes on ro->rw remount Boris Burkov
2020-11-18 23:06 ` [PATCH v7 03/12] btrfs: only mark bg->needs_free_space if free space tree is on Boris Burkov
2020-11-18 23:06 ` [PATCH v7 04/12] btrfs: create free space tree on ro->rw remount Boris Burkov
2020-11-18 23:06 ` [PATCH v7 05/12] btrfs: clear oneshot options on mount and remount Boris Burkov
2020-11-18 23:06 ` [PATCH v7 06/12] btrfs: clear free space tree on ro->rw remount Boris Burkov
2020-11-30 19:49   ` David Sterba
2020-11-18 23:06 ` [PATCH v7 07/12] btrfs: keep sb cache_generation consistent with space_cache Boris Burkov
2020-11-18 23:06 ` [PATCH v7 08/12] btrfs: use sb state to print space_cache mount option Boris Burkov
2020-11-18 23:06 ` [PATCH v7 09/12] btrfs: warn when remount will not change the free space tree Boris Burkov
2020-11-30 20:05   ` David Sterba
2020-11-18 23:06 ` [PATCH v7 10/12] btrfs: remove free space items when disabling space cache v1 Boris Burkov
2020-11-18 23:06 ` [PATCH v7 11/12] btrfs: skip space_cache v1 setup when not using it Boris Burkov
2020-11-18 23:06 ` Boris Burkov [this message]
2020-11-20 21:32 ` [PATCH v7 00/10] btrfs: free space tree mounting fixes David Sterba
2020-11-30 18:24   ` Boris Burkov
2020-11-30 20:29     ` David Sterba
2020-11-30 20:33 ` David Sterba

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