2021-08-19 08:57:02

by Jia-Ju Bai

Subject: [BUG] fs: dlm: possible ABBA deadlock

Hello,

My static analysis tool reports a possible ABBA deadlock in the dlm
filesystem in Linux 5.10:

dlm_recover_waiters_pre()
  mutex_lock(&ls->ls_waiters_mutex); --> line 5130
  recover_convert_waiter()
    _receive_convert_reply()
      lock_rsb()
        mutex_lock(&r->res_mutex); --> line 69

dlm_recover_waiters_post()
  lock_rsb()
    mutex_lock(&r->res_mutex); --> line 69
  mutex_lock(&ls->ls_waiters_mutex); --> line 5307

When dlm_recover_waiters_pre() and dlm_recover_waiters_post() are
concurrently executed, the deadlock can occur.

I am not quite sure whether this possible deadlock is real and how to
fix it if it is real.
Any feedback would be appreciated, thanks :)

Reported-by: TOTE Robot <[email protected]>


Best wishes,
Jia-Ju Bai

2021-08-19 15:59:29

by David Teigland

Subject: Re: [BUG] fs: dlm: possible ABBA deadlock

On Thu, Aug 19, 2021 at 04:54:57PM +0800, Jia-Ju Bai wrote:
> Hello,
>
> My static analysis tool reports a possible ABBA deadlock in the dlm
> filesystem in Linux 5.10:
>
> dlm_recover_waiters_pre()
> ? mutex_lock(&ls->ls_waiters_mutex); --> line 5130
> ? recover_convert_waiter()
> ??? _receive_convert_reply()
> ????? lock_rsb()
> ??????? mutex_lock(&r->res_mutex); --> line 69
>
> dlm_recover_waiters_post()
> ? lock_rsb()
> ??? mutex_lock(&r->res_mutex); --> line 69
> ? mutex_lock(&ls->ls_waiters_mutex); --> line 5307
>
> When dlm_recover_waiters_pre() and dlm_recover_waiters_post() are
> concurrently executed, the deadlock can occur.
>
> I am not quite sure whether this possible deadlock is real and how to fix it
> if it is real.
> Any feedback would be appreciated, thanks :)

They won't be concurrent, "pre" runs before recovery, and "post" is after.
Dave

2021-08-20 08:38:33

by Jia-Ju Bai

Subject: Re: [BUG] fs: dlm: possible ABBA deadlock

On 2021/8/19 23:55, David Teigland wrote:
> On Thu, Aug 19, 2021 at 04:54:57PM +0800, Jia-Ju Bai wrote:
>> Hello,
>>
>> My static analysis tool reports a possible ABBA deadlock in the dlm
>> filesystem in Linux 5.10:
>>
>> dlm_recover_waiters_pre()
>>   mutex_lock(&ls->ls_waiters_mutex); --> line 5130
>>   recover_convert_waiter()
>>     _receive_convert_reply()
>>       lock_rsb()
>>         mutex_lock(&r->res_mutex); --> line 69
>>
>> dlm_recover_waiters_post()
>>   lock_rsb()
>>     mutex_lock(&r->res_mutex); --> line 69
>>   mutex_lock(&ls->ls_waiters_mutex); --> line 5307
>>
>> When dlm_recover_waiters_pre() and dlm_recover_waiters_post() are
>> concurrently executed, the deadlock can occur.
>>
>> I am not quite sure whether this possible deadlock is real and how to fix it
>> if it is real.
>> Any feedback would be appreciated, thanks :)
> They won't be concurrent, "pre" runs before recovery, and "post" is after.

Okay, thanks for your reply :)


Best wishes,
Jia-Ju Bai