linux-toradex.git/block/blk-wbt.h, branch v7.0-rc2

blk-wbt: factor out a helper wbt_set_lat()

2026-02-02T14:05:19+00:00

To move implementation details inside blk-wbt.c, prepare to fix possible
deadlock to call wbt_init() while queue is frozen in the next patch.

Reviewed-by: Ming Lei 
Reviewed-by: Nilay Shroff 
Signed-off-by: Yu Kuai 
Reviewed-by: Hannes Reinecke 
Signed-off-by: Jens Axboe

block: fix race between wbt_enable_default and IO submission

2025-12-12T19:51:11+00:00

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 
Cc: Yu Kuai 
Cc: Guangwu Zhang 
Fixes: 78c271344b6f ("block: move wbt_enable_default() out of queue freezing from sched ->exit()")
Signed-off-by: Ming Lei 
Reviewed-by: Nilay Shroff 
Signed-off-by: Jens Axboe

blk-wbt: remove the separate write cache tracking

2023-12-26T16:28:10+00:00

Use the queue wide write back cache tracking insted of duplicating the
value in strut rq_wb.

Signed-off-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20231226090747.204969-1-hch@lst.de
Signed-off-by: Jens Axboe

blk-wbt: don't create wbt sysfs entry if CONFIG_BLK_WBT is disabled

2023-06-26T15:53:36+00:00

sysfs entry /sys/block/[device]/queue/wbt_lat_usec will be created even
if CONFIG_BLK_WBT is disabled, while read and write will always fail.
It doesn't make sense to create a sysfs entry that can't be accessed,
so don't create such entry.

Signed-off-by: Yu Kuai 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20230527010644.647900-2-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe

blk-wbt: move private information from blk-wbt.h to blk-wbt.c

2023-02-03T15:20:05+00:00

A large part of blk-wbt.h is only used in blk-wbt.c, so move it there.

Signed-off-by: Christoph Hellwig 
Acked-by: Tejun Heo 
Link: https://lore.kernel.org/r/20230203150400.3199230-11-hch@lst.de
Signed-off-by: Jens Axboe

blk-wbt: pass a gendisk to wbt_init

2023-02-03T15:20:05+00:00

Pass a gendisk to wbt_init to prepare for phasing out usage of the
request_queue in the blk-cgroup code.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Andreas Herrmann 
Acked-by: Tejun Heo 
Link: https://lore.kernel.org/r/20230203150400.3199230-10-hch@lst.de
Signed-off-by: Jens Axboe

blk-wbt: pass a gendisk to wbt_{enable,disable}_default

2023-02-03T15:20:05+00:00

Pass a gendisk to wbt_enable_default and wbt_disable_default to
prepare for phasing out usage of the request_queue in the blk-cgroup
code.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Andreas Herrmann 
Acked-by: Tejun Heo 
Link: https://lore.kernel.org/r/20230203150400.3199230-9-hch@lst.de
Signed-off-by: Jens Axboe

blk-wbt: don't show valid wbt_lat_usec in sysfs while wbt is disabled

2022-10-24T00:59:17+00:00

Currently, if wbt is initialized and then disabled by
wbt_disable_default(), sysfs will still show valid wbt_lat_usec, which
will confuse users that wbt is still enabled.

This patch shows wbt_lat_usec as zero if it's disabled.

Signed-off-by: Yu Kuai 
Reported-and-tested-by: Holger Hoffstätte 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20221019121518.3865235-5-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe

blk-wbt: make enable_state more accurate

2022-10-24T00:59:17+00:00

Currently, if user disable wbt through sysfs, 'enable_state' will be
'WBT_STATE_ON_MANUAL', which will be confusing. Add a new state
'WBT_STATE_OFF_MANUAL' to cover that case.

Signed-off-by: Yu Kuai 
Reviewed-by: Christoph Hellwig 
Link: https://lore.kernel.org/r/20221019121518.3865235-4-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe

blk-wbt: remove wbt_track stub

2022-03-31T18:58:38+00:00

cppcheck returns this warning
[block/blk-wbt.h:104] -> [block/blk-wbt.c:592]:
  (warning) Function 'wbt_track' argument order different:
  declaration 'rq, flags, ' definition 'rqos, rq, bio'

In commit c1c80384c8f4 ("block: remove external dependency on wbt_flags")
wbt_track was removed for the real declaration, its stub should
have been as well.

Signed-off-by: Tom Rix 
Link: https://lore.kernel.org/r/20220331185458.3427454-1-trix@redhat.com
Signed-off-by: Jens Axboe