linux-kernel - Re: [PATCH v2] blktrace: Fix potentail deadlock between delete & sysfs ops

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Date:   Thu, 17 Aug 2017 18:13:20 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] blktrace: Fix potentail deadlock between delete &
 sysfs ops

On Thu, 17 Aug 2017 17:27:22 -0400
Waiman Long <longman@...hat.com> wrote:


> It is actually what the patch is trying to do by checking for the
> deletion flag in the mutex_trylock loop. Please note that mutex does not
> guarantee FIFO ordering of lock acquisition. As a result, cpu1 may call
> mutex_lock() and wait for it while cpu2 can set the deletion flag later
> and get the mutex first before cpu1. So checking for the deletion flag
> before taking the mutex isn't enough.

Yeah, I figured that out already (crossed emails). BTW, how did you
trigger this warning. I'm playing around with adding loop devices,
volume groups, and logical volumes, and reading the trace files
created in the sysfs directory, then removing those items, but it's
not triggering the "delete" path. What operation deletes the partition?

Thanks

-- Steve