This is a note to let you know that I've just added the patch titled
blk-wbt: call rq_qos_add() after wb_normal is initialized
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
blk-wbt-call-rq_qos_add-after-wb_normal-is-initialized.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8c5035dfbb9475b67c82b3fdb7351236525bf52b Mon Sep 17 00:00:00 2001
From: Yu Kuai <yukuai3@xxxxxxxxxx>
Date: Tue, 13 Sep 2022 18:57:49 +0800
Subject: blk-wbt: call rq_qos_add() after wb_normal is initialized
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From: Yu Kuai <yukuai3@xxxxxxxxxx>
commit 8c5035dfbb9475b67c82b3fdb7351236525bf52b upstream.
Our test found a problem that wbt inflight counter is negative, which
will cause io hang(noted that this problem doesn't exist in mainline):
t1: device create t2: issue io
add_disk
blk_register_queue
wbt_enable_default
wbt_init
rq_qos_add
// wb_normal is still 0
/*
* in mainline, disk can't be opened before
* bdev_add(), however, in old kernels, disk
* can be opened before blk_register_queue().
*/
blkdev_issue_flush
// disk size is 0, however, it's not checked
submit_bio_wait
submit_bio
blk_mq_submit_bio
rq_qos_throttle
wbt_wait
bio_to_wbt_flags
rwb_enabled
// wb_normal is 0, inflight is not increased
wbt_queue_depth_changed(&rwb->rqos);
wbt_update_limits
// wb_normal is initialized
rq_qos_track
wbt_track
rq->wbt_flags |= bio_to_wbt_flags(rwb, bio);
// wb_normal is not 0，wbt_flags will be set
t3: io completion
blk_mq_free_request
rq_qos_done
wbt_done
wbt_is_tracked
// return true
__wbt_done
wbt_rqw_done
atomic_dec_return(&rqw->inflight);
// inflight is decreased
commit 8235b5c1e8c1 ("block: call bdev_add later in device_add_disk") can
avoid this problem, however it's better to fix this problem in wbt:
1) Lower kernel can't backport this patch due to lots of refactor.
2) Root cause is that wbt call rq_qos_add() before wb_normal is
initialized.
Fixes: e34cbd307477 ("blk-wbt: add general throttling mechanism")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220913105749.3086243-1-yukuai1@xxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
block/blk-wbt.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -840,6 +840,10 @@ int wbt_init(struct request_queue *q)
rwb->enable_state = WBT_STATE_ON_DEFAULT;
rwb->wc = 1;
rwb->rq_depth.default_depth = RWB_DEF_DEPTH;
+ rwb->min_lat_nsec = wbt_default_latency_nsec(q);
+
+ wbt_queue_depth_changed(&rwb->rqos);
+ wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
/*
* Assign rwb and add the stats callback.
@@ -847,10 +851,5 @@ int wbt_init(struct request_queue *q)
rq_qos_add(q, &rwb->rqos);
blk_stat_add_callback(q, rwb->cb);
- rwb->min_lat_nsec = wbt_default_latency_nsec(q);
-
- wbt_queue_depth_changed(&rwb->rqos);
- wbt_set_write_cache(q, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
-
return 0;
}
Patches currently in stable-queue which might be from yukuai3@xxxxxxxxxx are
queue-5.10/block-wbt-remove-unnecessary-invoking-of-wbt_update_limits-in-wbt_init.patch
queue-5.10/blk-wbt-call-rq_qos_add-after-wb_normal-is-initialized.patch
