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

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Date:   Wed, 16 Aug 2017 14:59:38 -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] blktrace: Fix potentail deadlock between delete & sysfs
 ops

On Wed, 16 Aug 2017 14:46:42 -0400
Waiman Long <longman@...hat.com> wrote:


> I haven't been thinking about RT tasks. You are right that it can be a
> problem in this case. I think I will have to revert back to use
> mutex_lock() if a RT task is running. Though in this case, the lock
> inversion problem will still be there. However, it is highly unlikely
> that a RT task will need to read write the block trace sysfs files.

And it is highly unlikely that the lock inversion will happen. But
let's not switch one bug with another. And with PREEMPT_RT coming, that
can boost tasks into being RT, it can make the likelihood of RT tasks
running normally non RT tasks higher.

-- Steve