[PATCH 1/3] bfq: Avoid false marking of bic as stably merged

[PATCH 1/3] bfq: Avoid false marking of bic as stably merged

[Jan Kara]

bfq_setup_cooperator() can mark bic as stably merged even though it
decides to not merge its bfqqs (when bfq_setup_merge() returns NULL).
Make sure to mark bic as stably merged only if we are really going to
merge bfqqs.

CC: stable@vger.kernel.org
Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index fec18118dc30..056399185c2f 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2762,9 +2762,12 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 				struct bfq_queue *new_bfqq =
 					bfq_setup_merge(bfqq, stable_merge_bfqq);
 
-				bic->stably_merged = true;
-				if (new_bfqq && new_bfqq->bic)
-					new_bfqq->bic->stably_merged = true;
+				if (new_bfqq) {
+					bic->stably_merged = true;
+					if (new_bfqq->bic)
+						new_bfqq->bic->stably_merged =
+									true;
+				}
 				return new_bfqq;
 			} else
 				return NULL;
-- 
2.26.2

[PATCH 2/3] bfq: Avoid merging queues with different parents

[Jan Kara]

It can happen that the parent of a bfqq changes between the moment we
decide two queues are worth to merge (and set bic->stable_merge_bfqq)
and the moment bfq_setup_merge() is called. This can happen e.g. because
the process submitted IO for a different cgroup and thus bfqq got
reparented. It can even happen that the bfqq we are merging with has
parent cgroup that is already offline and going to be destroyed in which
case the merge can lead to use-after-free issues such as:

BUG: KASAN: use-after-free in __bfq_deactivate_entity+0x9cb/0xa50
Read of size 8 at addr ffff88800693c0c0 by task runc:[2:INIT]/10544

CPU: 0 PID: 10544 Comm: runc:[2:INIT] Tainted: G            E     5.15.2-0.g5fb85fd-default #1 openSUSE Tumbleweed (unreleased) f1f3b891c72369aebecd2e43e4641a6358867c70
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014
Call Trace:
 <IRQ>
 dump_stack_lvl+0x46/0x5a
 print_address_description.constprop.0+0x1f/0x140
 ? __bfq_deactivate_entity+0x9cb/0xa50
 kasan_report.cold+0x7f/0x11b
 ? __bfq_deactivate_entity+0x9cb/0xa50
 __bfq_deactivate_entity+0x9cb/0xa50
 ? update_curr+0x32f/0x5d0
 bfq_deactivate_entity+0xa0/0x1d0
 bfq_del_bfqq_busy+0x28a/0x420
 ? resched_curr+0x116/0x1d0
 ? bfq_requeue_bfqq+0x70/0x70
 ? check_preempt_wakeup+0x52b/0xbc0
 __bfq_bfqq_expire+0x1a2/0x270
 bfq_bfqq_expire+0xd16/0x2160
 ? try_to_wake_up+0x4ee/0x1260
 ? bfq_end_wr_async_queues+0xe0/0xe0
 ? _raw_write_unlock_bh+0x60/0x60
 ? _raw_spin_lock_irq+0x81/0xe0
 bfq_idle_slice_timer+0x109/0x280
 ? bfq_dispatch_request+0x4870/0x4870
 __hrtimer_run_queues+0x37d/0x700
 ? enqueue_hrtimer+0x1b0/0x1b0
 ? kvm_clock_get_cycles+0xd/0x10
 ? ktime_get_update_offsets_now+0x6f/0x280
 hrtimer_interrupt+0x2c8/0x740

Fix the problem by checking that the parent of the two bfqqs we are
merging in bfq_setup_merge() is the same.

Link: https://lore.kernel.org/linux-block/20211125172809.GC19572@quack2.suse.cz/
CC: stable@vger.kernel.org
Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 056399185c2f..0da47f2ca781 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2638,6 +2638,14 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
 	if (process_refs == 0 || new_process_refs == 0)
 		return NULL;
 
+	/*
+	 * Make sure merged queues belong to the same parent. Parents could
+	 * have changed since the time we decided the two queues are suitable
+	 * for merging.
+	 */
+	if (new_bfqq->entity.parent != bfqq->entity.parent)
+		return NULL;
+
 	bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
 		new_bfqq->pid);
 
-- 
2.26.2

[PATCH 3/3] bfq: Split shared queues on move between cgroups

[Jan Kara]

When bfqq is shared by multiple processes it can happen that one of the
processes gets moved to a different cgroup (or just starts submitting IO
for different cgroup). In case that happens we need to split the merged
bfqq as otherwise we will have IO for multiple cgroups in one bfqq and
we will just account IO time to wrong entities etc.

CC: stable@vger.kernel.org
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-cgroup.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 24a5c5329bcd..1f5fb723bed7 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -730,8 +730,18 @@ static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
 
 	if (sync_bfqq) {
 		entity = &sync_bfqq->entity;
-		if (entity->sched_data != &bfqg->sched_data)
+		if (entity->sched_data != &bfqg->sched_data) {
+			/*
+			 * Moving bfqq that is shared with another process?
+			 * Split the queues at the nearest occasion as the
+			 * processes can be in different cgroups now.
+			 */
+			if (bfq_bfqq_coop(sync_bfqq)) {
+				bic->stably_merged = false;
+				bfq_mark_bfqq_split_coop(sync_bfqq);
+			}
 			bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
+		}
 	}
 
 	return bfqg;
-- 
2.26.2

Re: [PATCH 2/3] bfq: Avoid merging queues with different parents

[yukuai (C)]

在 2021/12/24 1:31, Jan Kara 写道:
> It can happen that the parent of a bfqq changes between the moment we
> decide two queues are worth to merge (and set bic->stable_merge_bfqq)
> and the moment bfq_setup_merge() is called. This can happen e.g. because
> the process submitted IO for a different cgroup and thus bfqq got
> reparented. It can even happen that the bfqq we are merging with has
> parent cgroup that is already offline and going to be destroyed in which
> case the merge can lead to use-after-free issues such as:
> 
> BUG: KASAN: use-after-free in __bfq_deactivate_entity+0x9cb/0xa50
> Read of size 8 at addr ffff88800693c0c0 by task runc:[2:INIT]/10544
> 
> CPU: 0 PID: 10544 Comm: runc:[2:INIT] Tainted: G            E     5.15.2-0.g5fb85fd-default #1 openSUSE Tumbleweed (unreleased) f1f3b891c72369aebecd2e43e4641a6358867c70
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014
> Call Trace:
>   <IRQ>
>   dump_stack_lvl+0x46/0x5a
>   print_address_description.constprop.0+0x1f/0x140
>   ? __bfq_deactivate_entity+0x9cb/0xa50
>   kasan_report.cold+0x7f/0x11b
>   ? __bfq_deactivate_entity+0x9cb/0xa50
>   __bfq_deactivate_entity+0x9cb/0xa50
>   ? update_curr+0x32f/0x5d0
>   bfq_deactivate_entity+0xa0/0x1d0
>   bfq_del_bfqq_busy+0x28a/0x420
>   ? resched_curr+0x116/0x1d0
>   ? bfq_requeue_bfqq+0x70/0x70
>   ? check_preempt_wakeup+0x52b/0xbc0
>   __bfq_bfqq_expire+0x1a2/0x270
>   bfq_bfqq_expire+0xd16/0x2160
>   ? try_to_wake_up+0x4ee/0x1260
>   ? bfq_end_wr_async_queues+0xe0/0xe0
>   ? _raw_write_unlock_bh+0x60/0x60
>   ? _raw_spin_lock_irq+0x81/0xe0
>   bfq_idle_slice_timer+0x109/0x280
>   ? bfq_dispatch_request+0x4870/0x4870
>   __hrtimer_run_queues+0x37d/0x700
>   ? enqueue_hrtimer+0x1b0/0x1b0
>   ? kvm_clock_get_cycles+0xd/0x10
>   ? ktime_get_update_offsets_now+0x6f/0x280
>   hrtimer_interrupt+0x2c8/0x740
> 
> Fix the problem by checking that the parent of the two bfqqs we are
> merging in bfq_setup_merge() is the same.
> 
> Link: https://lore.kernel.org/linux-block/20211125172809.GC19572@quack2.suse.cz/
> CC: stable@vger.kernel.org
> Fixes: 430a67f9d616 ("block, bfq: merge bursts of newly-created queues")
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>   block/bfq-iosched.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 056399185c2f..0da47f2ca781 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -2638,6 +2638,14 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
>   	if (process_refs == 0 || new_process_refs == 0)
>   		return NULL;
>   
> +	/*
> +	 * Make sure merged queues belong to the same parent. Parents could
> +	 * have changed since the time we decided the two queues are suitable
> +	 * for merging.
> +	 */
> +	if (new_bfqq->entity.parent != bfqq->entity.parent)
> +		return NULL;
> +
Hi,

This seems unnecessary, the caller of bfq_setup_merge() aready make sure
bfqq and new_bfqq are under the same bfqg. Am I missing something?

Thanks,
Kuai
>   	bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
>   		new_bfqq->pid);
>   
> 

Re: [PATCH 2/3] bfq: Avoid merging queues with different parents

[Jan Kara]

On Fri 24-12-21 09:45:02, yukuai (C) wrote:
> 在 2021/12/24 1:31, Jan Kara 写道:
> > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> > index 056399185c2f..0da47f2ca781 100644
> > --- a/block/bfq-iosched.c
> > +++ b/block/bfq-iosched.c
> > @@ -2638,6 +2638,14 @@ bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
> >   	if (process_refs == 0 || new_process_refs == 0)
> >   		return NULL;
> > +	/*
> > +	 * Make sure merged queues belong to the same parent. Parents could
> > +	 * have changed since the time we decided the two queues are suitable
> > +	 * for merging.
> > +	 */
> > +	if (new_bfqq->entity.parent != bfqq->entity.parent)
> > +		return NULL;
> > +
> Hi,
> 
> This seems unnecessary, the caller of bfq_setup_merge() aready make sure
> bfqq and new_bfqq are under the same bfqg. Am I missing something?

Not all the callers of bfq_setup_merge() check that queues belong to the
same cgroup (e.g. bfq_setup_cooperator() does not seem to check).

								Honza

> 
> Thanks,
> Kuai
> >   	bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
> >   		new_bfqq->pid);
> > 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR