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Date: Thu, 29 Jan 2009 05:42:27 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Chris Mason <chris.mason@oracle.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Matthew Wilcox <matthew@wil.cx>, Chuck Lever <cel@citi.umich.edu>,
       Nick Piggin <nickpiggin@yahoo.com.au>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, Ingo Molnar <mingo@elte.hu>
Subject: Re: [RFC v7] wait: prevent exclusive waiter starvation
Message-ID: <20090129044227.GA5231@redhat.com>
References: <20090121213813.GB23270@cmpxchg.org> <20090122202550.GA5726@redhat.com> <20090123095904.GA22890@cmpxchg.org> <20090123113541.GB12684@redhat.com> <20090123133050.GA19226@redhat.com> <20090126215957.GA3889@cmpxchg.org> <20090127032359.GA17359@redhat.com> <20090127193434.GA19673@cmpxchg.org> <20090127200544.GA28843@redhat.com> <20090128091453.GA22036@cmpxchg.org>
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On 01/28, Johannes Weiner wrote:
>
> Add abort_exclusive_wait() which removes the process' wait descriptor
> from the waitqueue, iff still queued, or wakes up the next waiter
> otherwise.  It does so under the waitqueue lock.  Racing with a wake
> up means the aborting process is either already woken (removed from
> the queue) and will wake up the next waiter, or it will remove itself
> from the queue and the concurrent wake up will apply to the next
> waiter after it.
>
> Use abort_exclusive_wait() in __wait_event_interruptible_exclusive()
> and __wait_on_bit_lock() when they were interrupted by other means
> than a wake up through the queue.

Imho, this all is right, and this patch should replace
lock_page_killable-avoid-lost-wakeups.patch (except for stable tree).

But I guess we need maintainer's opinion, we have them in cc ;)

Oleg.