[PATCH 5.15 192/731] bfq: fix waker_bfqq inconsistency crash

Greg Kroah-Hartman
2022-12-28T14:54:29Z

From: Khazhismel Kumykov <khazhy@chromium.org>

[ Upstream commit a1795c2ccb1e4c49220d2a0d381540024d71647c ]

This fixes crashes in bfq_add_bfqq_busy due to waker_bfqq being NULL,
but woken_list_node still being hashed. This would happen when
bfq_init_rq() expects a brand new allocated queue to be returned from
bfq_get_bfqq_handle_split() and unconditionally updates waker_bfqq
without resetting woken_list_node. Since we can always return oom_bfqq
when attempting to allocate, we cannot assume waker_bfqq starts as NULL.

Avoid setting woken_bfqq for oom_bfqq entirely, as it's not useful.

Crashes would have a stacktrace like:
[160595.656560] bfq_add_bfqq_busy+0x110/0x1ec
[160595.661142] bfq_add_request+0x6bc/0x980
[160595.666602] bfq_insert_request+0x8ec/0x1240
[160595.671762] bfq_insert_requests+0x58/0x9c
[160595.676420] blk_mq_sched_insert_request+0x11c/0x198
[160595.682107] blk_mq_submit_bio+0x270/0x62c
[160595.686759] __submit_bio_noacct_mq+0xec/0x178
[160595.691926] submit_bio+0x120/0x184
[160595.695990] ext4_mpage_readpages+0x77c/0x7c8
[160595.701026] ext4_readpage+0x60/0xb0
[160595.705158] filemap_read_page+0x54/0x114
[160595.711961] filemap_fault+0x228/0x5f4
[160595.716272] do_read_fault+0xe0/0x1f0
[160595.720487] do_fault+0x40/0x1c8

Tested by injecting random failures into bfq_get_queue, crashes go away
completely.

Fixes: 8ef3fc3a043c ("block, bfq: make shared queues inherit wakers")
Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20221108181030.1611703-1-khazhy@google.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/bfq-iosched.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7d8fe13573f6..f21b861a0d66 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6630,6 +6630,12 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
true, is_sync,
NULL);
+ if (unlikely(bfqq == &bfqd->oom_bfqq))
+ bfqq_already_existing = true;
+ } else
+ bfqq_already_existing = true;
+
+ if (!bfqq_already_existing) {
bfqq->waker_bfqq = old_bfqq->waker_bfqq;
bfqq->tentative_waker_bfqq = NULL;

@@ -6643,8 +6649,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
if (bfqq->waker_bfqq)
hlist_add_head(&bfqq->woken_list_node,
&bfqq->waker_bfqq->woken_list);
- } else
- bfqq_already_existing = true;
+ }
}
}

--
2.35.1