linux-kernel - Re: [BUG] fs: dlm: possible ABBA deadlock

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Date:   Thu, 19 Aug 2021 10:55:09 -0500
From:   David Teigland <teigland@...hat.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     cluster-devel@...hat.com, linux-kernel@...r.kernel.org
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