linux-kernel - Re: Poll CQ syncing problem

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Date:   Wed, 1 Mar 2017 15:51:24 +0100
From:   Christoph Hellwig <hch@....de>
To:     Noa Osherovich <noaos@...lanox.com>
Cc:     hch@....de, sagi@...mberg.me, linux-rdma@...r.kernel.org,
        Majd Dibbiny <majd@...lanox.com>, tj@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Poll CQ syncing problem

On Wed, Mar 01, 2017 at 04:30:26PM +0200, Noa Osherovich wrote:
> Analysis:
> Since ib_comp_wq isn't single threaded, two works can run in parallel for the same CQ,
> executing __ib_process_cq.

They shouldn't.  Each CQ has a single work_struct, and any given work_struct
should only be executing at once:

"Note that the flag ``WQ_NON_REENTRANT`` no longer exists as all
workqueues are now non-reentrant - any work item is guaranteed to be
executed by at most one worker system-wide at any given time."

> Since this function isn't thread safe and the wc array is shared, it causes a data corruption
> which eventually crashes in the MAD layer due to a double list_del of the same element.

This should not be the case.  What kernel version are you testing and does
it contain any patches touching core kernel code?