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Date:   Thu, 19 Aug 2021 10:55:09 -0500
From:   David Teigland <teigland@redhat.com>
To:     Jia-Ju Bai <baijiaju1990@gmail.com>
Cc:     cluster-devel@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [BUG] fs: dlm: possible ABBA deadlock
Message-ID: <20210819155509.GB21218@redhat.com>
References: <79f8d302-f53f-3891-965a-bcb460ab15ca@gmail.com>
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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