From: Manfred Spraul <manfred@colorfullife.com>
To: npiggin@suse.de
Cc: Andrew Morton <akpm@linux-foundation.org>,
Nadia Derbey <Nadia.Derbey@bull.net>,
Pierre Peiffer <peifferp@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [patch 3/4] ipc: sem preempt improve
Date: Sun, 16 Aug 2009 15:20:35 +0200 [thread overview]
Message-ID: <4A8807A3.3080604@colorfullife.com> (raw)
In-Reply-To: <20090811111607.144736971@suse.de>
On 08/11/2009 01:09 PM, npiggin@suse.de wrote:
> The strange sysv semaphore wakeup scheme has a kind of busy-wait lock
> involved, which could deadlock if preemption is enabled during the
> "lock".
>
> It is an implementation detail (due to a spinlock being held) that this
> is actually the case. However if "spinlocks" are made preemptible, or if
> the sem lock is changed to a sleeping lock for example, then the wakeup
> would become buggy. So this might be a bugfix for -rt kernels.
>
> Imagine waker being preempted by wakee and never clearing IN_WAKEUP --
> if wakee has higher RT priority then there is a priority inversion deadlock.
> Even if there is not a priority inversion to cause a deadlock, then there
> is still time wasted spinning.
>
> Signed-off-by: Nick Piggin<npiggin@suse.de>
>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
next prev parent reply other threads:[~2009-08-16 13:19 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-11 11:09 [patch 0/4] ipc sem improvements npiggin
2009-08-11 11:09 ` [patch 1/4] ipc: sem optimise undo list search npiggin
2009-08-16 13:17 ` Manfred Spraul
2009-08-11 11:09 ` [patch 2/4] ipc: sem use list operations npiggin
2009-08-16 13:18 ` Manfred Spraul
2009-08-11 11:09 ` [patch 3/4] ipc: sem preempt improve npiggin
2009-08-16 13:20 ` Manfred Spraul [this message]
2009-08-11 11:09 ` [patch 4/4] ipc: sem optimise simple operations npiggin
2009-08-11 18:19 ` Manfred Spraul
2009-08-11 18:23 ` Zach Brown
2009-08-12 4:07 ` Nick Piggin
2009-08-12 18:35 ` Manfred Spraul
2009-08-14 8:58 ` Nick Piggin
2009-08-14 17:53 ` Manfred Spraul
2009-08-11 20:07 ` Cyrill Gorcunov
2009-08-12 4:48 ` Nick Piggin
2009-08-12 5:43 ` Cyrill Gorcunov
2009-08-14 18:48 ` Manfred Spraul
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