I've had an oops on kernel boot due to NULL pointer deference
linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6
I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED
In this case cfq_ref_get_cfqg() defined as
static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
{
return NULL;
}
So following call trace is simply NOOP
cfq_set_request()
rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
Which later result in OOPS on bio insertion
cfq_insert_request
-> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...)
-> spin_lock_irqsave(&blkg->stats_lock, flags);
Bad commit.
>From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001
From: Vivek Goyal <[email protected]>
Date: Wed, 21 Apr 2010 17:44:16 +0200
Subject: [PATCH] blkio: Fix blkio crash during rq stat update
On Wed, Apr 28, 2010 at 07:36:02PM +0400, Dmitry Monakhov wrote:
> Vivek Goyal <[email protected]> writes:
>
> > On Wed, Apr 28, 2010 at 04:44:51PM +0400, Dmitry Monakhov wrote:
> >>
> >> I've had an oops on kernel boot due to NULL pointer deference
> >> linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6
> >> I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED
> >> In this case cfq_ref_get_cfqg() defined as
> >> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
> >> {
> >> return NULL;
> >> }
> >> So following call trace is simply NOOP
> >> cfq_set_request()
> >> rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
> >>
> >> Which later result in OOPS on bio insertion
> >> cfq_insert_request
> >> -> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...)
> >> -> spin_lock_irqsave(&blkg->stats_lock, flags);
> >>
> >> Bad commit.
> >> >From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001
> >> From: Vivek Goyal <[email protected]>
> >> Date: Wed, 21 Apr 2010 17:44:16 +0200
> >> Subject: [PATCH] blkio: Fix blkio crash during rq stat update
> >
> > Dmitry, this patch should fix the issue. Can you please give it a try.
> Yes. the issue is gone.
> >
> > Jens, I know you don't like this form of cfq_ref_get_cfqg(), but this
> > seems to be the simplest solution to fix it.
> IMHO following fix is simpler, and cleaner.
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 286008c..0f3eb70 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -1094,7 +1094,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
>
> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
> {
> - return NULL;
> + return cfqg;
> }
Thanks Dmitry. I like it. simpler.
Vivek
On Wed, Apr 28, 2010 at 04:44:51PM +0400, Dmitry Monakhov wrote:
>
> I've had an oops on kernel boot due to NULL pointer deference
> linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6
> I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED
> In this case cfq_ref_get_cfqg() defined as
> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
> {
> return NULL;
> }
> So following call trace is simply NOOP
> cfq_set_request()
> rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
>
> Which later result in OOPS on bio insertion
> cfq_insert_request
> -> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...)
> -> spin_lock_irqsave(&blkg->stats_lock, flags);
>
> Bad commit.
> >From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001
> From: Vivek Goyal <[email protected]>
> Date: Wed, 21 Apr 2010 17:44:16 +0200
> Subject: [PATCH] blkio: Fix blkio crash during rq stat update
Hi Dmitry,
Thanks for reporting the issue. I am cooking up a patch now.
Vivek
On Wed, Apr 28, 2010 at 04:44:51PM +0400, Dmitry Monakhov wrote:
>
> I've had an oops on kernel boot due to NULL pointer deference
> linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6
> I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED
> In this case cfq_ref_get_cfqg() defined as
> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
> {
> return NULL;
> }
> So following call trace is simply NOOP
> cfq_set_request()
> rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
>
> Which later result in OOPS on bio insertion
> cfq_insert_request
> -> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...)
> -> spin_lock_irqsave(&blkg->stats_lock, flags);
>
> Bad commit.
> >From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001
> From: Vivek Goyal <[email protected]>
> Date: Wed, 21 Apr 2010 17:44:16 +0200
> Subject: [PATCH] blkio: Fix blkio crash during rq stat update
Dmitry, this patch should fix the issue. Can you please give it a try.
Jens, I know you don't like this form of cfq_ref_get_cfqg(), but this
seems to be the simplest solution to fix it.
cfq-iosched: fix cfq crash with CFQ_GROUP_IOSCHED=n
Dmitry reported an oops with CFQ when booted with BLK_CGROUP=y and
CFQ_GROUP_IOSCHED=n. This patch fixes it.
We maintain a root group even if group ioscheduling is not enabled. Hence
don't store NULL in elevator_private3 in that case.
Signed-off-by: Vivek Goyal <[email protected]>
---
block/cfq-iosched.c | 11 ++++-------
1 files changed, 4 insertions(+), 7 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 286008c..5aa5364 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1002,10 +1002,9 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
return cfqg;
}
-static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
+static inline void cfq_ref_get_cfqg(struct cfq_group *cfqg)
{
atomic_inc(&cfqg->ref);
- return cfqg;
}
static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
@@ -1092,10 +1091,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
return &cfqd->root_group;
}
-static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
-{
- return NULL;
-}
+static inline void cfq_ref_get_cfqg(struct cfq_group *cfqg) {}
static inline void
cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
@@ -3574,7 +3570,8 @@ new_queue:
rq->elevator_private = cic;
rq->elevator_private2 = cfqq;
- rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
+ rq->elevator_private3 = cfqq->cfqg;
+ cfq_ref_get_cfqg(cfqq->cfqg);
return 0;
queue_fail:
--
1.6.2.5
On Wed, Apr 28 2010, Dmitry Monakhov wrote:
> Vivek Goyal <[email protected]> writes:
>
> > On Wed, Apr 28, 2010 at 04:44:51PM +0400, Dmitry Monakhov wrote:
> >>
> >> I've had an oops on kernel boot due to NULL pointer deference
> >> linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6
> >> I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED
> >> In this case cfq_ref_get_cfqg() defined as
> >> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
> >> {
> >> return NULL;
> >> }
> >> So following call trace is simply NOOP
> >> cfq_set_request()
> >> rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
> >>
> >> Which later result in OOPS on bio insertion
> >> cfq_insert_request
> >> -> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...)
> >> -> spin_lock_irqsave(&blkg->stats_lock, flags);
> >>
> >> Bad commit.
> >> >From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001
> >> From: Vivek Goyal <[email protected]>
> >> Date: Wed, 21 Apr 2010 17:44:16 +0200
> >> Subject: [PATCH] blkio: Fix blkio crash during rq stat update
> >
> > Dmitry, this patch should fix the issue. Can you please give it a try.
> Yes. the issue is gone.
> >
> > Jens, I know you don't like this form of cfq_ref_get_cfqg(), but this
> > seems to be the simplest solution to fix it.
> IMHO following fix is simpler, and cleaner.
Agreed, that's much better. I'll add it, thanks.
--
Jens Axboe