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

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Message-ID: <ee8f13dc-10aa-55bf-f152-5c73ae0a1d03@redhat.com>
Date:   Wed, 16 Aug 2017 15:07:25 -0400
From:   Waiman Long <longman@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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 08/16/2017 02:59 PM, Steven Rostedt wrote:
> 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

That is true too:-)

> 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

I am thinking about maybe letting a RT task to sleep a tiny amount of
time instead of calling schedule(). Hopefully, that will allow a
lower-priority task to make forward progress.

Cheers,
Longman