lkml.org 
[lkml]   [2021]   [Oct]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [f2fs-dev] [PATCH] f2fs: remove circular locking between sb_internal and fs_reclaim
From
On 2021/10/22 0:44, Daeho Jeong wrote:
> There is a deadlock between sb_internal lock (sb_start_intwrite()) and
> dquot related lock.
> It's because we call f2fs_truncate(), which eventually calls
> dquot_initialize(), while holding sb_internal lock.
> So, I called dquot_initialize() in advance to make the 2nd calling of
> it in f2fs_truncate() ineffective.
> This is similar with the thing in f2fs_evict_inode() in inode.c

Well, if dquot_initialize() fails in f2fs_drop_inode(), will we still run
into deadlock?

Thanks,

>
> Thanks,
>
> On Thu, Oct 21, 2021 at 5:11 AM Chao Yu <chao@kernel.org> wrote:
>>
>> 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);
>>>
>>>

\
 
 \ /
  Last update: 2021-10-22 17:33    [W:0.138 / U:0.248 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site