This is a note to let you know that I've just added the patch titled
btrfs: sysfs: init devices outside of the chunk_mutex
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-sysfs-init-devices-outside-of-the-chunk_mutex.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit cf7e4ad88d8cb110a445e430d5f97eff65a368fe
Author: Josef Bacik <josef@xxxxxxxxxxxxxx>
Date: Tue Sep 1 08:09:01 2020 -0400
btrfs: sysfs: init devices outside of the chunk_mutex
[ Upstream commit ca10845a56856fff4de3804c85e6424d0f6d0cde ]
While running btrfs/061, btrfs/073, btrfs/078, or btrfs/178 we hit the
following lockdep splat:
======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc3+ #4 Not tainted
------------------------------------------------------
kswapd0/100 is trying to acquire lock:
ffff96ecc22ef4a0 (&delayed_node->mutex){+.+.}-{3:3}, at: __btrfs_release_delayed_node.part.0+0x3f/0x330
but task is already holding lock:
ffffffff8dd74700 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (fs_reclaim){+.+.}-{0:0}:
fs_reclaim_acquire+0x65/0x80
slab_pre_alloc_hook.constprop.0+0x20/0x200
kmem_cache_alloc+0x37/0x270
alloc_inode+0x82/0xb0
iget_locked+0x10d/0x2c0
kernfs_get_inode+0x1b/0x130
kernfs_get_tree+0x136/0x240
sysfs_get_tree+0x16/0x40
vfs_get_tree+0x28/0xc0
path_mount+0x434/0xc00
__x64_sys_mount+0xe3/0x120
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #2 (kernfs_mutex){+.+.}-{3:3}:
__mutex_lock+0x7e/0x7e0
kernfs_add_one+0x23/0x150
kernfs_create_link+0x63/0xa0
sysfs_do_create_link_sd+0x5e/0xd0
btrfs_sysfs_add_devices_dir+0x81/0x130
btrfs_init_new_device+0x67f/0x1250
btrfs_ioctl+0x1ef/0x2e20
__x64_sys_ioctl+0x83/0xb0
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #1 (&fs_info->chunk_mutex){+.+.}-{3:3}:
__mutex_lock+0x7e/0x7e0
btrfs_chunk_alloc+0x125/0x3a0
find_free_extent+0xdf6/0x1210
btrfs_reserve_extent+0xb3/0x1b0
btrfs_alloc_tree_block+0xb0/0x310
alloc_tree_block_no_bg_flush+0x4a/0x60
__btrfs_cow_block+0x11a/0x530
btrfs_cow_block+0x104/0x220
btrfs_search_slot+0x52e/0x9d0
btrfs_insert_empty_items+0x64/0xb0
btrfs_insert_delayed_items+0x90/0x4f0
btrfs_commit_inode_delayed_items+0x93/0x140
btrfs_log_inode+0x5de/0x2020
btrfs_log_inode_parent+0x429/0xc90
btrfs_log_new_name+0x95/0x9b
btrfs_rename2+0xbb9/0x1800
vfs_rename+0x64f/0x9f0
do_renameat2+0x320/0x4e0
__x64_sys_rename+0x1f/0x30
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #0 (&delayed_node->mutex){+.+.}-{3:3}:
__lock_acquire+0x119c/0x1fc0
lock_acquire+0xa7/0x3d0
__mutex_lock+0x7e/0x7e0
__btrfs_release_delayed_node.part.0+0x3f/0x330
btrfs_evict_inode+0x24c/0x500
evict+0xcf/0x1f0
dispose_list+0x48/0x70
prune_icache_sb+0x44/0x50
super_cache_scan+0x161/0x1e0
do_shrink_slab+0x178/0x3c0
shrink_slab+0x17c/0x290
shrink_node+0x2b2/0x6d0
balance_pgdat+0x30a/0x670
kswapd+0x213/0x4c0
kthread+0x138/0x160
ret_from_fork+0x1f/0x30
other info that might help us debug this:
Chain exists of:
&delayed_node->mutex --> kernfs_mutex --> fs_reclaim
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(fs_reclaim);
lock(kernfs_mutex);
lock(fs_reclaim);
lock(&delayed_node->mutex);
*** DEADLOCK ***
3 locks held by kswapd0/100:
#0: ffffffff8dd74700 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30
#1: ffffffff8dd65c50 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x115/0x290
#2: ffff96ed2ade30e0 (&type->s_umount_key#36){++++}-{3:3}, at: super_cache_scan+0x38/0x1e0
stack backtrace:
CPU: 0 PID: 100 Comm: kswapd0 Not tainted 5.9.0-rc3+ #4
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
Call Trace:
dump_stack+0x8b/0xb8
check_noncircular+0x12d/0x150
__lock_acquire+0x119c/0x1fc0
lock_acquire+0xa7/0x3d0
? __btrfs_release_delayed_node.part.0+0x3f/0x330
__mutex_lock+0x7e/0x7e0
? __btrfs_release_delayed_node.part.0+0x3f/0x330
? __btrfs_release_delayed_node.part.0+0x3f/0x330
? lock_acquire+0xa7/0x3d0
? find_held_lock+0x2b/0x80
__btrfs_release_delayed_node.part.0+0x3f/0x330
btrfs_evict_inode+0x24c/0x500
evict+0xcf/0x1f0
dispose_list+0x48/0x70
prune_icache_sb+0x44/0x50
super_cache_scan+0x161/0x1e0
do_shrink_slab+0x178/0x3c0
shrink_slab+0x17c/0x290
shrink_node+0x2b2/0x6d0
balance_pgdat+0x30a/0x670
kswapd+0x213/0x4c0
? _raw_spin_unlock_irqrestore+0x41/0x50
? add_wait_queue_exclusive+0x70/0x70
? balance_pgdat+0x670/0x670
kthread+0x138/0x160
? kthread_create_worker_on_cpu+0x40/0x40
ret_from_fork+0x1f/0x30
This happens because we are holding the chunk_mutex at the time of
adding in a new device. However we only need to hold the
device_list_mutex, as we're going to iterate over the fs_devices
devices. Move the sysfs init stuff outside of the chunk_mutex to get
rid of this lockdep splat.
CC: stable@xxxxxxxxxxxxxxx # 4.4.x: f3cd2c58110dad14e: btrfs: sysfs, rename device_link add/remove functions
CC: stable@xxxxxxxxxxxxxxx # 4.4.x
Reported-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 58910a0a3e4a4..00e7816dc9a1e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2728,9 +2728,6 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
btrfs_set_super_num_devices(fs_info->super_copy,
orig_super_num_devices + 1);
- /* add sysfs device entry */
- btrfs_sysfs_add_device_link(fs_devices, device);
-
/*
* we've got more storage, clear any full flags on the space
* infos
@@ -2738,6 +2735,10 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
btrfs_clear_space_info_full(fs_info);
mutex_unlock(&fs_info->chunk_mutex);
+
+ /* Add sysfs device entry */
+ btrfs_sysfs_add_device_link(fs_devices, device);
+
mutex_unlock(&fs_devices->device_list_mutex);
if (seeding_dev) {
