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Date: Thu, 20 Nov 2008 10:27:06 +0530 From: Nikanth Karthikesan <knikanth@...e.de> To: Jens Axboe <jens.axboe@...cle.com> Cc: linux-kernel@...r.kernel.org, Fabio Checconi <fchecconi@...il.com> Subject: Re: [PATCH] Exiting queue and task might race to free cic On Wednesday 19 November 2008 19:45:31 Jens Axboe wrote: > On Wed, Nov 19 2008, Nikanth Karthikesan wrote: > Not sure this is enough, we probably need to copy the key to ensure that > we get a fresh value. How does this look? > Agreed. Read barrier required. But the compiler hint, "likely" can stay? diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 6a062ee..4504b94 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1318,7 +1318,15 @@ static void cfq_exit_single_io_context(struct io_context *ioc, unsigned long flags; spin_lock_irqsave(q->queue_lock, flags); - __cfq_exit_single_io_context(cfqd, cic); + + /* + * Ensure we get a fresh copy of the ->key to prevent + * race between exiting task and queue + */ + smp_read_barrier_depends(); + if (likely(cic->key)) + __cfq_exit_single_io_context(cfqd, cic); + spin_unlock_irqrestore(q->queue_lock, flags); } } > Did you actually trigger this, or is it just from code inspection? > No. But I am looking at another bug report on Suse Kernel where the bug is triggered during reboot when the kernel thread usb_stor_scan_thread exits. Thanks Nikanth Karthikesan -- 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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