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Subject[PATCH AUTOSEL 4.18 107/131] f2fs: avoid potential deadlock in f2fs_sbi_store
Date
From: Jaegeuk Kim <jaegeuk@kernel.org>

[ Upstream commit a1933c09ef84c2fd187e05b560ddc6e1267d6508 ]

[ 155.018460] ======================================================
[ 155.021431] WARNING: possible circular locking dependency detected
[ 155.024339] 4.18.0-rc3+ #5 Tainted: G OE
[ 155.026879] ------------------------------------------------------
[ 155.029783] umount/2901 is trying to acquire lock:
[ 155.032187] 00000000c4282f1f (kn->count#130){++++}, at: kernfs_remove+0x1f/0x30
[ 155.035439]
[ 155.035439] but task is already holding lock:
[ 155.038892] 0000000056e4307b (&type->s_umount_key#41){++++}, at: deactivate_super+0x33/0x50
[ 155.042602]
[ 155.042602] which lock already depends on the new lock.
[ 155.042602]
[ 155.047465]
[ 155.047465] the existing dependency chain (in reverse order) is:
[ 155.051354]
[ 155.051354] -> #1 (&type->s_umount_key#41){++++}:
[ 155.054768] f2fs_sbi_store+0x61/0x460 [f2fs]
[ 155.057083] kernfs_fop_write+0x113/0x1a0
[ 155.059277] __vfs_write+0x36/0x180
[ 155.061250] vfs_write+0xbe/0x1b0
[ 155.063179] ksys_write+0x55/0xc0
[ 155.065068] do_syscall_64+0x60/0x1b0
[ 155.067071] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 155.069529]
[ 155.069529] -> #0 (kn->count#130){++++}:
[ 155.072421] __kernfs_remove+0x26f/0x2e0
[ 155.074452] kernfs_remove+0x1f/0x30
[ 155.076342] kobject_del.part.5+0xe/0x40
[ 155.078354] f2fs_put_super+0x12d/0x290 [f2fs]
[ 155.080500] generic_shutdown_super+0x6c/0x110
[ 155.082655] kill_block_super+0x21/0x50
[ 155.084634] kill_f2fs_super+0x9c/0xc0 [f2fs]
[ 155.086726] deactivate_locked_super+0x3f/0x70
[ 155.088826] cleanup_mnt+0x3b/0x70
[ 155.090584] task_work_run+0x93/0xc0
[ 155.092367] exit_to_usermode_loop+0xf0/0x100
[ 155.094466] do_syscall_64+0x162/0x1b0
[ 155.096312] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 155.098603]
[ 155.098603] other info that might help us debug this:
[ 155.098603]
[ 155.102418] Possible unsafe locking scenario:
[ 155.102418]
[ 155.105134] CPU0 CPU1
[ 155.107037] ---- ----
[ 155.108910] lock(&type->s_umount_key#41);
[ 155.110674] lock(kn->count#130);
[ 155.113010] lock(&type->s_umount_key#41);
[ 155.115608] lock(kn->count#130);

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
fs/f2fs/sysfs.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 5344e21853b2..bca1236fd6fa 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -287,8 +287,10 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
bool gc_entry = (!strcmp(a->attr.name, "gc_urgent") ||
a->struct_type == GC_THREAD);

- if (gc_entry)
- down_read(&sbi->sb->s_umount);
+ if (gc_entry) {
+ if (!down_read_trylock(&sbi->sb->s_umount))
+ return -EAGAIN;
+ }
ret = __sbi_store(a, sbi, buf, count);
if (gc_entry)
up_read(&sbi->sb->s_umount);
--
2.17.1
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