linux-kernel - Re: 2.6.27-rc4: lots of 'in_atomic():1, irqs

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Message-ID: <18614.24929.952454.829021@notabene.brown>
Date:	Thu, 28 Aug 2008 18:27:13 +1000
From:	Neil Brown <neilb@...e.de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, jurriaan <thunder7@...all.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.27-rc4: lots of 'in_atomic():1, irqs_disabled():0' with  software-raid1

On Thursday August 28, jens.axboe@...cle.com wrote:
> On Thu, Aug 28 2008, Andrew Morton wrote:
> > 
> > Cant sleep inside rcu_read_lock(), with CONFIG_PREEMPT_RCU=n, at least.
> > 
> > Dunno if it's legal if CONFIG_PREEMPT_RCU=y.  Hopefully not - that
> > would be insane.  But I've failed to keep up with rcu goings-on
> > recently.
> 
> Doh right, we of course can't block inside a RCU section. Then
> bitmap.c:write_sb_page() wants fixing:
> 
>         rcu_read_lock();
>         rdev_for_each_rcu(...)
>                 md_super_write(...)
>                         bio_alloc(GFP_NOIO, 1);
> 
> Neil?


Yes......

And not only can't I call bio_alloc inside the rcu_read_lock, I also
cannot call submit_bio, as that can do a mempool alloc for a request
structure.
I can get around that by putting the bios on the ->biolist that
md_super_wait will resubmit requests from.  But I still need to
allocate those bios.
Maybe I can count how many there need to be, then allocate them and
make a list, then pass them down into md_super_write.
It's a bit ugly but it should work.

I think I'll have to think about it a bit more.

Thanks,
NeilBrown
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