From fb889bf5d394f9de2326e33a2a24e9aacafd1509 Mon Sep 17 00:00:00 2001

From: Jan Kara <jack@suse.cz>

Date: Tue, 21 Dec 2021 19:37:32 +0100

Subject: [PATCH 2/9] bfq: Avoid merging queues with different parents

References: bsc#1197926

Patch-mainline: submitted, in linux-block tree

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")

Tested-by: "yukuai (C)" <yukuai3@huawei.com>

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 6d122c28086e..7d00b21ebe5d 100644

--- a/block/bfq-iosched.c

+++ b/block/bfq-iosched.c

@@ -2758,6 +2758,14 @@ 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);

-- 

2.34.1