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

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Message-ID: <20170816141749.6c11d14c@gandalf.local.home>
Date:   Wed, 16 Aug 2017 14:17:49 -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 14:14:36 -0400
Waiman Long <longman@...hat.com> wrote:

> > You also just turned the mutex into a spinlock. What happens if we just
> > preempted the owner of bdev->bd_mutex and are an RT task with higher
> > priority? This will turn into a live lock.
> >  
> >> +		schedule();
> >> +	}
> >>    
> 
> That is OK because I used schedule() instead of cpu_relax() for
> inserting delay.

Please explain to me how that is OK? schedule is a nop if the current
task is the highest priority task running, and it preempted the owner
of the lock. Nothing will actually schedule.

-- Steve