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SubjectRe: [f2fs-dev] [PATCH] f2fs: remove circular locking between sb_internal and fs_reclaim
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On 2021/10/15 3:05, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
>
> We detected the below circular locking dependency between sb_internal
> and fs_reclaim. So, removed it by calling dquot_initialize() before
> sb_start_intwrite().
>
> ======================================================
> WARNING: possible circular locking dependency detected
> ------------------------------------------------------
> kswapd0/133 is trying to acquire lock:
> ffffff80d5fb9680 (sb_internal#2){.+.+}-{0:0}, at: evict+0xd4/0x2f8
>
> but task is already holding lock:
> ffffffda597c93a8 (fs_reclaim){+.+.}-{0:0}, at:
> __fs_reclaim_acquire+0x4/0x50
>
> which lock already depends on the new lock.
> ...
> other info that might help us debug this:
>
> Chain exists of:
>
> sb_internal#2 --> &s->s_dquot.dqio_sem --> fs_reclaim
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(fs_reclaim);
> lock(&s->s_dquot.dqio_sem);
> lock(fs_reclaim);
> lock(sb_internal#2);

Sorry, I still didn't get the root cause of this deadlock issue, could
you please explain more about this?

And why calling dquot_initialize() in drop_inode() could break the
circular locking dependency?

Thanks,

>
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
> fs/f2fs/super.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 86eeb019cc52..a133932333c5 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1370,6 +1370,8 @@ static int f2fs_drop_inode(struct inode *inode)
> /* should remain fi->extent_tree for writepage */
> f2fs_destroy_extent_node(inode);
>
> + dquot_initialize(inode);
> +
> sb_start_intwrite(inode->i_sb);
> f2fs_i_size_write(inode, 0);
>
>

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