linux-kernel - RE: [BUG] infiniband: hw: hfi1: possible ABBA deadlock in pio_wait() and sc

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Date:   Thu, 23 Sep 2021 19:06:24 +0000
From:   "Marciniszyn, Mike" <mike.marciniszyn@...nelisnetworks.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>,
        "Dalessandro, Dennis" <dennis.dalessandro@...nelisnetworks.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [BUG] infiniband: hw: hfi1: possible ABBA deadlock in pio_wait()
 and sc_disable()

> 
> Hello,
> 
> My static analysis tool reports a possible ABBA deadlock in the hfi1 driver in
> Linux 5.10:
> 
> sc_disable()
>    write_seqlock(&sc->waitlock); --> Line 956 (Lock A)
>    hfi1_qp_wakeup()
>      spin_lock_irqsave(&qp->s_lock, flags); --> Line 441 (Lock B)
> 
> pio_wait()
>    spin_lock_irqsave(&qp->s_lock, flags); --> Line 939 (Lock B)
>    write_seqlock(&sc->waitlock); --> Line 941 (Lock A)
> 
> When sc_disable() and pio_wait() 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 <oslab@...nghua.edu.cn>
> 
> 
> Best wishes,
> Jia-Ju Bai

I don't think this can occur, but all other callers to hfi1_qp_wakeup() stash the waiters into an array.

I will workup a patch to move the linked list of waiters to a local, drop the lock, and process the local array of waiters.

Mike