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| author | Usama Arif <usama.arif@linux.dev> | 2026-06-16 07:15:18 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2026-06-16 10:07:36 -0600 |
| commit | fad156c2af227f42ca796cbb20ddc354a6dd9932 (patch) | |
| tree | ab68093aae12f62ff5f16d34cf027cbc9d9a0a4d /include | |
| parent | fd38b75c4b43295b10d69772a46d1c74dbd6fc81 (diff) | |
| download | ath-fad156c2af227f42ca796cbb20ddc354a6dd9932.tar.gz | |
block: invalidate cached plug timestamp after task switch
blk_time_get_ns() caches ktime_get_ns() in current->plug->cur_ktime
and marks the task with PF_BLOCK_TS. That cache is only valid while the
task keeps running; if the task is switched out, wall-clock time
advances and the cached value must not be reused when the task runs again.
The existing invalidation covers explicit plug flushes through
__blk_flush_plug(), and the schedule() / rtmutex paths through
sched_update_worker(). It does not cover in-kernel preemption paths such
as preempt_schedule(), preempt_schedule_notrace(), and
preempt_schedule_irq(), which enter __schedule(SM_PREEMPT) directly and
return without calling sched_update_worker().
As a result, a task preempted while holding a plug with PF_BLOCK_TS set
can reuse a stale plug->cur_ktime after it is scheduled back in. blk-iocost
then consumes that stale timestamp through ioc_now(), producing stale vnow
values for throttle decisions, and through ioc_rqos_done(), inflating
on-queue time and feeding false missed-QoS samples into vrate
adjustment.
Move the schedule-side invalidation to finish_task_switch(), which runs
for the scheduled-in task after every actual context switch regardless
of which schedule entry point was used. Keep __blk_flush_plug() as the
explicit flush/finish-plug invalidation path, and remove only the
PF_BLOCK_TS handling from sched_update_worker().
Fixes: 06b23f92af87 ("block: update cached timestamp post schedule/preemption")
Cc: stable@vger.kernel.org
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Link: https://patch.msgid.link/20260616141604.328820-3-usama.arif@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/blkdev.h | 16 |
1 files changed, 6 insertions, 10 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 5070851cf9249..9213a5716f95a 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1222,16 +1222,12 @@ static inline void blk_flush_plug(struct blk_plug *plug, bool async) __blk_flush_plug(plug, async); } -/* - * tsk == current here - */ -static inline void blk_plug_invalidate_ts(struct task_struct *tsk) +static __always_inline void blk_plug_invalidate_ts(void) { - struct blk_plug *plug = tsk->plug; - - if (plug) - plug->cur_ktime = 0; - current->flags &= ~PF_BLOCK_TS; + if (unlikely(current->flags & PF_BLOCK_TS)) { + current->plug->cur_ktime = 0; + current->flags &= ~PF_BLOCK_TS; + } } int blkdev_issue_flush(struct block_device *bdev); @@ -1257,7 +1253,7 @@ static inline void blk_flush_plug(struct blk_plug *plug, bool async) { } -static inline void blk_plug_invalidate_ts(struct task_struct *tsk) +static inline void blk_plug_invalidate_ts(void) { } |