On Tue 08-11-22 10:10:29, Khazhismel Kumykov wrote:
> 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@xxxxxxxxxx>
Looks good. Thanks! Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> 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 7ea427817f7f..ca04ec868c40 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -6784,6 +6784,12 @@ 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;
>
> @@ -6797,8 +6803,7 @@ 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;
> + }
> }
> }
>
> --
> 2.38.1.431.g37b22c650d-goog
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
