linux-kernel - Re: [BUG] scsi: qedi: possible ABBA deadlock in qedi_process_tmf_resp() and qedi_process_cmd_cleanup

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Date:   Tue, 8 Feb 2022 11:10:56 -0600
From:   Mike Christie <michael.christie@...cle.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, njavali@...vell.com,
        mrangankar@...vell.com, GR-QLogic-Storage-Upstream@...vell.com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] scsi: qedi: possible ABBA deadlock in
 qedi_process_tmf_resp() and qedi_process_cmd_cleanup_resp()

On 2/8/22 5:23 AM, Jia-Ju Bai wrote:
> Hello,
> 
> My static analysis tool reports a possible ABBA deadlock in the qedi driver in Linux 5.16:
> 
> qedi_process_tmf_resp()
>   spin_lock(&session->back_lock); --> Line 201 (Lock A)
>   spin_lock(&qedi_conn->tmf_work_lock); --> Line 230 (Lock B)
> 
> qedi_process_cmd_cleanup_resp()
>   spin_lock_bh(&qedi_conn->tmf_work_lock); --> Line 752 (Lock B)
>   spin_lock_bh(&conn->session->back_lock); --> Line 784 (Lock A)
> 
> When qedi_process_tmf_resp() and qedi_process_cmd_cleanup_resp() 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 :)
> 

That looks like a valid deadlock. I'll send a patch. Thanks.

> Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
> 
> 
> Best wishes,
> Jia-Ju Bai