| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20090709195941.GE30832@redhat.com>
Date: Thu, 9 Jul 2009 15:59:41 -0400
From: Vivek Goyal <vgoyal@...hat.com>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: Jeff Moyer <jmoyer@...hat.com>, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in
cfq_find_alloc_queue()
On Thu, Jul 09, 2009 at 07:38:23PM +0200, Jens Axboe wrote:
> On Thu, Jul 09 2009, Vivek Goyal wrote:
> > On Sat, Jun 27, 2009 at 08:26:17PM +0200, Jens Axboe wrote:
> > > On Fri, Jun 26 2009, Jeff Moyer wrote:
> > > > Jens Axboe <jens.axboe@...cle.com> writes:
> > > >
> > > > > Setup an emergency fallback cfqq that we allocate at IO scheduler init
> > > > > time. If the slab allocation fails in cfq_find_alloc_queue(), we'll just
> > > > > punt IO to that cfqq instead. This ensures that cfq_find_alloc_queue()
> > > > > never fails without having to ensure free memory.
> > > > >
> > > > > Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> > > > > ---
> > > > > block/cfq-iosched.c | 124 +++++++++++++++++++++++++++-----------------------
> > > > > 1 files changed, 67 insertions(+), 57 deletions(-)
> > > > >
> > > > > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> > > > > index c760ae7..91e7e0b 100644
> > > > > --- a/block/cfq-iosched.c
> > > > > +++ b/block/cfq-iosched.c
> > > > > + /*
> > > > > + * Fallback dummy cfqq for extreme OOM conditions
> > > > > + */
> > > > > + struct cfq_queue oom_cfqq;
> > > >
> > > > OK, so you're embedding a cfqq into the cfqd. That's 136 bytes, so I
> > > > guess that's not too bad.
> > > >
> > > > > + /*
> > > > > + * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
> > > > > + * Grab a permanent reference to it, so that the normal code flow
> > > > > + * will not attempt to free it.
> > > > > + */
> > > > > + cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
> > > > > + atomic_inc(&cfqd->oom_cfqq.ref);
> > > > > +
> > > >
> > > > I guess this is so we never try to free it, good. ;)
> > > >
> > > > One issue I have with this patch is that, if a task happens to run into
> > > > this condition, there is no way out. It will always have the oom_cfqq
> > > > as it's cfqq. Can't we fix that if we recover from the OOM condition?
> > >
> > > Yeah, I fixed that about an hour after posting the patches. See:
> > >
> > > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=0370bc158cb1d5faa4b8a38c0de3211f0fd5bd64
> > >
> >
> > Hi Jens,
> >
> > I think above patch might not fix the issue of an oom_cfqq getting stuck
> > with an io context. The reason being that once we allocate the cfqq, it
> > will be cached in cic and once next request comes, we will retrieve it
> > from cic and never call cfq_get_queue()/cfq_find_alloc_queue().
> >
> > I think we probably need to do cfqq == oom_cfqq check in cfq_set_request()
> > also.
>
> Yes good catch, this is needed too! Can you please send as a "real"
> patch with signed-off-by added? Thanks!
Sure. Here you go.
In case memory is scarce, we now default to oom_cfqq. Once memory is
available again, we should allocate a new cfqq and stop using oom_cfqq for
a particular io context.
Once a new request comes in, check if we are using oom_cfqq, and if yes,
try to allocate a new cfqq.
Tested the patch by forcing the use of oom_cfqq and upon next request thread
realized that it was using oom_cfqq and it allocated a new cfqq.
Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
---
block/cfq-iosched.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux5/block/cfq-iosched.c
===================================================================
--- linux5.orig/block/cfq-iosched.c 2009-07-04 13:58:48.000000000 -0400
+++ linux5/block/cfq-iosched.c 2009-07-09 15:56:59.000000000 -0400
@@ -2311,7 +2311,7 @@ cfq_set_request(struct request_queue *q,
goto queue_fail;
cfqq = cic_to_cfqq(cic, is_sync);
- if (!cfqq) {
+ if (!cfqq || cfqq == &cfqd->oom_cfqq) {
cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);
cic_set_cfqq(cic, cfqq, is_sync);
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists