Re: [PATCH] f2fs: avoid potential deadlock in f2fs_sbi_store

From: Chao Yu
Date: Mon Jul 16 2018 - 03:18:52 EST


On 2018/7/15 9:10, Jaegeuk Kim wrote:
> [ 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);
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>

Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>

Thanks,