linux-kernel - Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all part of PROVE

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Date:   Wed, 23 Aug 2017 18:39:03 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Byungchul Park <byungchul.park@....com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Dave Chinner <david@...morbit.com>, Tejun Heo <tj@...nel.org>,
        johannes@...solutions.net
Subject: Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all
 part of PROVE_LOCKING

Peter, I am all confused and I am still trying to understand your email.
In particular, because I no longer understand the lockdep annotations in
workqueue.c, it turns out I forgot everything...

On 08/22, Peter Zijlstra wrote:
>
> I am however slightly puzzled by the need of flush_work() to take Q,
> what deadlock potential is there?

Do you really mean flush_work()? Or start_flush_work() ?

> It was added by Oleg in commit:
>
>   a67da70dc095 ("workqueues: lockdep annotations for flush_work()")

No, these annotations were moved later into start_flush, iiuc...

This

	lock_map_acquire(&work->lockdep_map);
	lock_map_release(&work->lockdep_map);

was added by another commit 0976dfc1d0cd80a4e9dfaf87bd8744612bde475a
"workqueue: Catch more locking problems with flush_work()", and at
first glance it is fine.

At the same time, I have a vague feeling that (perhaps) we can remove
these 2 annotations if we change process_one_work() and start_flush_work(),
not sure...

Oleg.