linux-kernel - [PATCH 0/1] x86, ticketlock: spin_unlock

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Date:	Mon, 1 Dec 2014 22:33:57 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <Waiman.Long@...com>, linux-kernel@...r.kernel.org
Subject: [PATCH 0/1] x86, ticketlock: spin_unlock_wait() can livelock

Please review, I'm afraid I could miss something.

OTOH, this almost looks like a bug to me. And in fact I have a bug
report which looks as if spin_unlock_wait() actually spins "forever"
until the system panics, although most probably the are other problems
in kernel/sched which lead to rq->lock contention.

Do we need a barrier() in arch_spin_unlock_wait() ? I guess no, and
the current code doesn't have it.

Perhaps it should use __ticket_lock_spinning() like arch_spin_lock() ?

And probably we should add the lockdep annotations.

Oleg.

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