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SubjectRe: WARNING in 2.6.25-07422-gb66e1f1
On Sunday May 4, jens.axboe@oracle.com wrote:
> On Sun, May 04 2008, Jacek Luczak wrote:
> > Hi,
> >
> > I've CC:-ed few guys which may help.
> >
> > Prakash Punnoor pisze:
> > > Hi, I got this on boot:
> > >
> > > usb 2-1.3: new full speed USB device using ehci_hcd and address 3
> > > usb 2-1.3: configuration #1 chosen from 1 choice
> > > Clocksource tsc unstable (delta = -117343945 ns)
> > > ------------[ cut here ]------------
> > > WARNING: at include/linux/blkdev.h:443 blk_remove_plug+0x7d/0x90()
...
>
> Looks like it caught a real bug there - unfortunately we have to check
> for ->queue_lock here as well, if this is another stacked devices and
> not the bottom device. Does this make the warning go away for you?
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 087eee0..958f26b 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -3264,6 +3264,8 @@ static void raid5_unplug_device(struct request_queue *q)
> unsigned long flags;
>
> spin_lock_irqsave(&conf->device_lock, flags);
> + if (q->queue_lock)
> + spin_lock(q->queue_lock);
>
> if (blk_remove_plug(q)) {
> conf->seq_flush++;
> @@ -3271,6 +3273,8 @@ static void raid5_unplug_device(struct request_queue *q)
> }
> md_wakeup_thread(mddev->thread);
>
> + if (q->queue_lock)
> + spin_unlock(q->queue_lock);
> spin_unlock_irqrestore(&conf->device_lock, flags);
>
> unplug_slaves(mddev);
>

I suspect that will just cause more problems, as the 'q' for an md
device never gets ->queue_lock initialised.
I suspect the correct thing to do is set
q->queue_lock = &conf->device_lock;

at some stage, probably immediately after device_lock is initialised
in 'run'.

I was discussing this with Dan Williams starting
http://marc.info/?l=linux-raid&m=120951839903995&w=4
though we don't have an agreed patch yet.

I'm wondering why you mention the issues of stacked devices though. I
don't see how it applies. Could you explain?

Thanks,
NeilBrown


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