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author | Yu Kuai <yukuai3@huawei.com> | 2022-09-13 13:57:49 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-10-30 11:41:16 +0300 |
commit | 910ba49b33450a878128adc7d9c419dd97efd923 (patch) | |
tree | 5a9cfae05cca0bc2b7d334b357207f0899a51476 /Documentation/sphinx-static | |
parent | 392536023da18086d57565e716ed50193869b8e7 (diff) | |
download | linux-910ba49b33450a878128adc7d9c419dd97efd923.tar.xz |
blk-wbt: call rq_qos_add() after wb_normal is initialized
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@vger.kernel.org>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20220913105749.3086243-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/sphinx-static')
0 files changed, 0 insertions, 0 deletions