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Message-ID: <6e038fa4-563a-2690-2a62-b92df117714a@gmail.com>
Date:   Thu, 20 Oct 2022 19:13:32 +0200
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Subject: Re: [BUG] infiniband: sw: rdmavt: possible ABBA deadlocks in
 rvt_ruc_loopback()
Content-Language: en-US
To:     Jia-Ju Bai <baijiaju1990@gmail.com>,
        dennis.dalessandro@cornelisnetworks.com, jgg@ziepe.ca,
        Leon Romanovsky <leon@kernel.org>
Cc:     linux-rdma@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <afe67a8e-82b8-9a47-0832-527c652cc66e@gmail.com>
From:   Niels Dossche <dossche.niels@gmail.com>
In-Reply-To: <afe67a8e-82b8-9a47-0832-527c652cc66e@gmail.com>
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On 20/10/2022 15:37, Jia-Ju Bai wrote:
> Hello,
> 
> My static analysis tool reports several possible ABBA deadlock in the rdmavt driver in Linux 5.18:
> 
> rvt_ruc_loopback()
>   spin_lock_irqsave(&sqp->s_lock, flags); --> Line 3190 (Lock A)
>   spin_lock(&sqp->r_lock); --> Line 3195 (Lock B)
> 
> rvt_qp_mr_clean()
>   spin_lock_irq(&qp->r_lock); --> Line 698 (Lock B)
>   spin_lock(&qp->s_lock); --> Line 700 (Lock A)
> 
> rvt_rc_timeout()
>   spin_lock_irqsave(&qp->r_lock, flags); --> Line 2595 (Lock B)
>   spin_lock(&qp->s_lock); --> Line 2596 (Lock A)
> 
> rvt_modify_qp()
>   spin_lock_irq(&qp->r_lock); --> Line 1419 (Lock B)
>   spin_lock(&qp->s_lock); --> Line 1421(Lock A)
> 
> _rvt_reset_qp()
>   spin_lock_irq(&qp->r_lock); --> Line 907 (Lock B)
>   spin_lock(&qp->s_lock); --> Line 909 (Lock A)
> 
> rvt_reset_qp()
>   spin_lock_irq(&qp->r_lock); --> Line 936 (Lock B)
>   spin_lock(&qp->s_lock); --> Line 938 (Lock A)
> 
> When rvt_ruc_loopback() is concurrently executed with rvt_qp_mr_clean(), rvt_rc_timeout(), rvt_modify_qp(), _rvt_reset_qp() or rvt_reset_qp(), the deadlocks can occur.
> 
> I am not quite sure whether these possible deadlocks are real and how to fix them if real.
> Any feedback would be appreciated, thanks :)
> 
> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
> 
> 
> Best wishes,
> Jia-Ju Bai


Hi


I don't know whether this deadlock is real or not, but I wrote the offending code.
If it's a real bug, I'm sorry about that.
If that's the case the bug is also present in 2 other places of rvt_ruc_loopback() in v5.19+:

1)
spin_lock_irqsave(&sqp->s_lock, flags); --> Line 3133
spin_lock(&sqp->r_lock); --> Line 3137

2)
spin_lock_irqsave(&sqp->s_lock, flags); --> Line 3192
spin_lock(&sqp->r_lock); --> Line 3193


Kind regards
Niels