Messages in this thread | | | Date | Tue, 6 Jun 2006 09:23:48 +0200 | From | Jens Axboe <> | Subject | Re: 2.6.17-rc5-mm3 - crash in cfq_queue_empty() after iosched change |
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On Tue, Jun 06 2006, Jens Axboe wrote: > On Mon, Jun 05 2006, Valdis.Kletnieks@vt.edu wrote: > > I've been hitting this about once every two weeks for a while now, > > probably back to a 2.6.16-rc or so. It always bites at the same time > > while my laptop was at a point very late in bootup. I finally caught > > one when I had pen, paper, *and* time to chase it a bit rather than > > reboot. Sorry for the very partial traceback, it's not a good CTS day > > and I didn't have a digital camera handy. > > > > BUG: Unable to handle kernel NULL pointer dereference at 0x0000005c > > EIP at cfq_queue_empty+0x9/0x15 > > call trace: > > elv_queue_empty+0x20/0x22 > > ide_do_request+0xa4/0x788 > > ide_intr+0x1ec/0x236 > > handle_IRQ_eent+0x27/0x52 > > handle_level_IRQ+0xb6 > > do_IRQ+0x5d/0x78 > > common_interrupt+0x1a/0x20 > > > > In my .config: > > > > CONFIG_IOSCHED_NOOP=y > > CONFIG_IOSCHED_AS=y > > CONFIG_IOSCHED_DEADLINE=y > > CONFIG_IOSCHED_CFQ=y > > CONFIG_DEFAULT_IOSCHED="anticipatory" > > > > This happened very soon (within a few milliseconds or two) after my /etc/rc.local did: > > > > echo cfq >| /sys/block/hda/queue/scheduler > > > > (The next executable statement in /etc/rc.local is this: > > echo noop >| /sys/block/hdb/queue/scheduler and 'last sysfs file' still > > pointed at /dev/hda). > > > > It *looks* like the problem is in elevator_switch() in block/elevator.c: > > > > while (q->rq.elvpriv) { > > blk_remove_plug(q); > > q->request_fn(q); > > spin_unlock_irq(q->queue_lock); > > msleep(10); > > spin_lock_irq(q->queue_lock); > > elv_drain_elevator(q); > > } > > > > this--> spin_unlock_irq(q->queue_lock); > > > > /* > > * unregister old elevator data > > */ > > elv_unregister_queue(q); > > old_elevator = q->elevator; > > > > /* > > * attach and start new elevator > > */ > > if (elevator_attach(q, e)) > > goto fail; > > > > should be down here someplace, after elevator_attach(), I suspect? > > Looks like the disk popped an IRQ after we had installed the > > iosched_cfq.ops[] but q->elevator->elevator_data hadn't been > > initialized yet... > > > > (I'd attach a patch, except I'm not positive I have the diagnosis > > right?) > > I think your analysis is pretty good, there's definitely a period there > where we don't want the queueing invoked. Does this help?
Tested here, switched 50 times between the various io schedulers while the queue was fully loaded. JFYI.
-- Jens Axboe
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