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9869d3a6fe
When wbt_enable_default() is moved out of queue freezing in elevator_change(),
it can cause the wbt inflight counter to become negative (-1), leading to hung
tasks in the writeback path. Tasks get stuck in wbt_wait() because the counter
is in an inconsistent state.
The issue occurs because wbt_enable_default() could race with IO submission,
allowing the counter to be decremented before proper initialization. This manifests
as:
rq_wait[0]:
inflight: -1
has_waiters: True
rwb_enabled() checks the state, which can be updated exactly between wbt_wait()
(rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter
will become negative.
And results in hung task warnings like:
task:kworker/u24:39 state:D stack:0 pid:14767
Call Trace:
rq_qos_wait+0xb4/0x150
wbt_wait+0xa9/0x100
__rq_qos_throttle+0x24/0x40
blk_mq_submit_bio+0x672/0x7b0
...
Fix this by:
1. Splitting wbt_enable_default() into:
- __wbt_enable_default(): Returns true if wbt_init() should be called
- wbt_enable_default(): Wrapper for existing callers (no init)
- wbt_init_enable_default(): New function that checks and inits WBT
2. Using wbt_init_enable_default() in blk_register_queue() to ensure
proper initialization during queue registration
3. Move wbt_init() out of wbt_enable_default() which is only for enabling
disabled wbt from bfq and iocost, and wbt_init() isn't needed. Then the
original lock warning can be avoided.
4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling
code since it's no longer needed
This ensures WBT is properly initialized before any IO can be submitted,
preventing the counter from going negative.
Cc: Nilay Shroff <nilay@linux.ibm.com>
Cc: Yu Kuai <yukuai@fnnas.com>
Cc: Guangwu Zhang <guazhang@redhat.com>
Fixes: 78c271344b ("block: move wbt_enable_default() out of queue freezing from sched ->exit()")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
34 lines
735 B
C
34 lines
735 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef WB_THROTTLE_H
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#define WB_THROTTLE_H
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#ifdef CONFIG_BLK_WBT
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int wbt_init(struct gendisk *disk);
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void wbt_init_enable_default(struct gendisk *disk);
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void wbt_disable_default(struct gendisk *disk);
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void wbt_enable_default(struct gendisk *disk);
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u64 wbt_get_min_lat(struct request_queue *q);
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void wbt_set_min_lat(struct request_queue *q, u64 val);
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bool wbt_disabled(struct request_queue *);
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u64 wbt_default_latency_nsec(struct request_queue *);
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#else
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static inline void wbt_init_enable_default(struct gendisk *disk)
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{
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}
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static inline void wbt_disable_default(struct gendisk *disk)
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{
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}
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static inline void wbt_enable_default(struct gendisk *disk)
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{
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}
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#endif /* CONFIG_BLK_WBT */
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#endif
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