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Message-ID: <20061211045830.GB5339@in.ibm.com> Date: Mon, 11 Dec 2006 10:28:31 +0530 From: Srivatsa Vaddagiri <vatsa@...ibm.com> To: Ingo Molnar <mingo@...e.hu> Cc: Andrew Morton <akpm@...l.org>, Bjorn Helgaas <bjorn.helgaas@...com>, linux-kernel@...r.kernel.org, Myron Stowe <myron.stowe@...com>, Jens Axboe <axboe@...nel.dk>, Dipankar <dipankar@...ibm.com>, Gautham shenoy <ego@...ibm.com> Subject: Re: workqueue deadlock On Sun, Dec 10, 2006 at 09:26:16AM +0100, Ingo Molnar wrote: > something like the pseudocode further below - when applied to a data > structure it has semantics and scalability close to that of > preempt_disable(), but it is still preemptible and the lock is specific. Ingo, The psuedo-code you have provided can still fail to avoid the deadlock reported by Bjorn Helgaas earlier in this thread: http://lkml.org/lkml/2006/12/6/352 Thread1->flush_workqueue->mutex_lock(cpu4's hotplug_lock) Thread2(keventd)->run_workqueue->som_work_fn-> .. flush_workqueue->mutex_lock(cpu4's hotplug_lock) Both deadlock with each other. All this mess could easily be avoided if we implement a reference-count based cpu_hotplug_lock(), as suggested by Arjan and Linus before and implemented by Gautham here: http://lkml.org/lkml/2006/10/26/65 -- Regards, vatsa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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