Messages in this thread Patch in this message | | | Date | Mon, 15 Dec 2008 19:44:41 +0100 | From | Jens Axboe <> | Subject | Re: next-20081215: kernel BUG at block/cfq-iosched.c:1243 |
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On Mon, Dec 15 2008, Alexander Beregalov wrote: > 2008/12/15 Jens Axboe <jens.axboe@oracle.com>: > >> [ 23.080733] kernel BUG at block/cfq-iosched.c:1243! > >> [ 23.080733] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC > > > Odd, is it reproducible? What is your .config? > Yes, it is > > Config is in attach
It's weird, because the only change for CFQ in that area is the one below. Does the oops go away if you back this out?
From 030a3f02bb42fad91ae84c99924fe3ee162a634d Mon Sep 17 00:00:00 2001 From: Jens Axboe <jens.axboe@oracle.com> Date: Fri, 12 Dec 2008 15:56:31 +0100 Subject: [PATCH] cfq-iosched: fix race between exiting queue and exiting task
Original patch from Nikanth Karthikesan <knikanth@suse.de>
When a queue exits the queue lock is taken and cfq_exit_queue() would free all the cic's associated with the queue.
But when a task exits, cfq_exit_io_context() gets cic one by one and then locks the associated queue to call __cfq_exit_single_io_context. It looks like between getting a cic from the ioc and locking the queue, the queue might have exited on another cpu.
Fix this by rechecking the cfq_io_context queue key inside the queue lock again, and not calling into __cfq_exit_single_io_context() if somebody beat us to it.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com> --- block/cfq-iosched.c | 9 +++++++++ 1 files changed, 9 insertions(+), 0 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index ee8a90c..8a2485d 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1314,7 +1314,16 @@ static void cfq_exit_single_io_context(struct io_context *ioc, unsigned long flags; spin_lock_irqsave(q->queue_lock, flags); + + /* + * Ensure we get a fresh copy of the ->key to prevent + * race between exiting task and queue + */ + smp_read_barrier_depends(); + if (cic->key) + __cfq_exit_single_io_context(cfqd, cic); __cfq_exit_single_io_context(cfqd, cic); + spin_unlock_irqrestore(q->queue_lock, flags); } } -- 1.6.0.4.755.g6e139
-- Jens Axboe
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