[PATCH 5.7 026/204] btrfs: sysfs: use NOFS for device creation

Greg Kroah-Hartman
2020-08-20T13:14:59Z

From: Josef Bacik <josef@toxicpanda.com>

commit a47bd78d0c44621efb98b525d04d60dc4d1a79b0 upstream.

Dave hit this splat during testing btrfs/078:

======================================================
WARNING: possible circular locking dependency detected
5.8.0-rc6-default+ #1191 Not tainted
------------------------------------------------------
kswapd0/75 is trying to acquire lock:
ffffa040e9d04ff8 (&delayed_node->mutex){+.+.}-{3:3}, at: __btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]

but task is already holding lock:
ffffffff8b0c8040 (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:

-> #2 (fs_reclaim){+.+.}-{0:0}:
__lock_acquire+0x56f/0xaa0
lock_acquire+0xa3/0x440
fs_reclaim_acquire.part.0+0x25/0x30
__kmalloc_track_caller+0x49/0x330
kstrdup+0x2e/0x60
__kernfs_new_node.constprop.0+0x44/0x250
kernfs_new_node+0x25/0x50
kernfs_create_link+0x34/0xa0
sysfs_do_create_link_sd+0x5e/0xd0
btrfs_sysfs_add_devices_dir+0x65/0x100 [btrfs]
btrfs_init_new_device+0x44c/0x12b0 [btrfs]
btrfs_ioctl+0xc3c/0x25c0 [btrfs]
ksys_ioctl+0x68/0xa0
__x64_sys_ioctl+0x16/0x20
do_syscall_64+0x50/0xe0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&fs_info->chunk_mutex){+.+.}-{3:3}:
__lock_acquire+0x56f/0xaa0
lock_acquire+0xa3/0x440
__mutex_lock+0xa0/0xaf0
btrfs_chunk_alloc+0x137/0x3e0 [btrfs]
find_free_extent+0xb44/0xfb0 [btrfs]
btrfs_reserve_extent+0x9b/0x180 [btrfs]
btrfs_alloc_tree_block+0xc1/0x350 [btrfs]
alloc_tree_block_no_bg_flush+0x4a/0x60 [btrfs]
__btrfs_cow_block+0x143/0x7a0 [btrfs]
btrfs_cow_block+0x15f/0x310 [btrfs]
push_leaf_right+0x150/0x240 [btrfs]
split_leaf+0x3cd/0x6d0 [btrfs]
btrfs_search_slot+0xd14/0xf70 [btrfs]
btrfs_insert_empty_items+0x64/0xc0 [btrfs]
__btrfs_commit_inode_delayed_items+0xb2/0x840 [btrfs]
btrfs_async_run_delayed_root+0x10e/0x1d0 [btrfs]
btrfs_work_helper+0x2f9/0x650 [btrfs]
process_one_work+0x22c/0x600
worker_thread+0x50/0x3b0
kthread+0x137/0x150
ret_from_fork+0x1f/0x30

-> #0 (&delayed_node->mutex){+.+.}-{3:3}:
check_prev_add+0x98/0xa20
validate_chain+0xa8c/0x2a00
__lock_acquire+0x56f/0xaa0
lock_acquire+0xa3/0x440
__mutex_lock+0xa0/0xaf0
__btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]
btrfs_evict_inode+0x3bf/0x560 [btrfs]
evict+0xd6/0x1c0
dispose_list+0x48/0x70
prune_icache_sb+0x54/0x80
super_cache_scan+0x121/0x1a0
do_shrink_slab+0x175/0x420
shrink_slab+0xb1/0x2e0
shrink_node+0x192/0x600
balance_pgdat+0x31f/0x750
kswapd+0x206/0x510
kthread+0x137/0x150
ret_from_fork+0x1f/0x30

other info that might help us debug this:

Chain exists of:
&delayed_node->mutex --> &fs_info->chunk_mutex --> fs_reclaim

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(fs_reclaim);
lock(&fs_info->chunk_mutex);
lock(fs_reclaim);
lock(&delayed_node->mutex);

*** DEADLOCK ***

3 locks held by kswapd0/75:
#0: ffffffff8b0c8040 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30
#1: ffffffff8b0b50b8 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x54/0x2e0
#2: ffffa040e057c0e8 (&type->s_umount_key#26){++++}-{3:3}, at: trylock_super+0x16/0x50

stack backtrace:
CPU: 2 PID: 75 Comm: kswapd0 Not tainted 5.8.0-rc6-default+ #1191
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
Call Trace:
dump_stack+0x78/0xa0
check_noncircular+0x16f/0x190
check_prev_add+0x98/0xa20
validate_chain+0xa8c/0x2a00
__lock_acquire+0x56f/0xaa0
lock_acquire+0xa3/0x440
? __btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]
__mutex_lock+0xa0/0xaf0
? __btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]
? __lock_acquire+0x56f/0xaa0
? __btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]
? lock_acquire+0xa3/0x440
? btrfs_evict_inode+0x138/0x560 [btrfs]
? btrfs_evict_inode+0x2fe/0x560 [btrfs]
? __btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]
__btrfs_release_delayed_node.part.0+0x3f/0x310 [btrfs]
btrfs_evict_inode+0x3bf/0x560 [btrfs]
evict+0xd6/0x1c0
dispose_list+0x48/0x70
prune_icache_sb+0x54/0x80
super_cache_scan+0x121/0x1a0
do_shrink_slab+0x175/0x420
shrink_slab+0xb1/0x2e0
shrink_node+0x192/0x600
balance_pgdat+0x31f/0x750
kswapd+0x206/0x510
? _raw_spin_unlock_irqrestore+0x3e/0x50
? finish_wait+0x90/0x90
? balance_pgdat+0x750/0x750
kthread+0x137/0x150
? kthread_stop+0x2a0/0x2a0
ret_from_fork+0x1f/0x30

This is because we're holding the chunk_mutex while adding this device
and adding its sysfs entries. We actually hold different locks in
different places when calling this function, the dev_replace semaphore
for instance in dev replace, so instead of moving this call around
simply wrap it's operations in NOFS.

CC: stable@vger.kernel.org # 4.14+
Reported-by: David Sterba <dsterba@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/sysfs.c | 3 +++
1 file changed, 3 insertions(+)

--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -1273,7 +1273,9 @@ int btrfs_sysfs_add_devices_dir(struct b
{
int error = 0;
struct btrfs_device *dev;
+ unsigned int nofs_flag;

+ nofs_flag = memalloc_nofs_save();
list_for_each_entry(dev, &fs_devices->devices, dev_list) {

if (one_device && one_device != dev)
@@ -1301,6 +1303,7 @@ int btrfs_sysfs_add_devices_dir(struct b
break;
}
}
+ memalloc_nofs_restore(nofs_flag);

return error;
}