linux-kernel - Re: [PATCH 3/9] IB: add a helper to safely drain a QP

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Date:	Wed, 18 Nov 2015 09:59:15 +0200
From:	Sagi Grimberg <sagig@....mellanox.co.il>
To:	Bart Van Assche <bart.vanassche@...disk.com>,
	Christoph Hellwig <hch@....de>, linux-rdma@...r.kernel.org
Cc:	axboe@...com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/9] IB: add a helper to safely drain a QP



On 17/11/2015 19:06, Bart Van Assche wrote:
> On 11/15/2015 01:34 AM, Sagi Grimberg wrote:
>> This is taken from srp, and srp drains using a recv wr due to a race
>> causing a use-after-free condition in srp which re-posts a recv buffer
>> in the recv completion handler.
>
> Hello Sagi,
>
> Would it be possible to clarify this ? Does this refer to an existing
> race or a race that would only occur if the code would be modified ?

I was referring to a bug that srp_destroy_qp() was design to
address:

commit 7dad6b2e440d810273946b0e7092a8fe043c3b8a
Author: Bart Van Assche <bvanassche@....org>
Date:   Tue Oct 21 18:00:35 2014 +0200

     IB/srp: Fix a race condition triggered by destroying a queue pair

     At least LID reassignment can trigger a race condition in the SRP
     initiator driver, namely the receive completion handler trying to
     post a request on a QP during or after QP destruction and before
     the CQ's have been destroyed. Avoid this race by modifying a QP
     into the error state and by waiting until all receive completions
     have been processed before destroying a QP.

     Reported-by: Max Gurtuvoy <maxg@...lanox.com>
     Signed-off-by: Bart Van Assche <bvanassche@....org>
     Reviewed-by: Sagi Grimberg <sagig@...lanox.com>
     Signed-off-by: Christoph Hellwig <hch@....de>
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