Re: 2.6.27-rc4: lots of 'in_atomic():1, irqs_disabled():0' with software-raid1

[Neil Brown <neilb@suse.de>]

On Thursday August 28, jens.axboe@oracle.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