Re: [PATCH v3] block/blk-iocost: annotate ioc_pd_stat reads with data_race()

[Tejun Heo]

On Tue, Aug 04, 2026 at 01:41:20PM +0800, Tao Cui wrote:
> From: Tao Cui <cuitao@xxxxxxxxxx>
> 
> ioc_pd_stat() reads ioc->enabled, ioc->vtime_base_rate, and
> iocg->last_stat without holding ioc->lock, which trips KCSAN since
> ioc_adjust_base_vrate() and iocg_flush_stat_upward() write those
> fields under ioc->lock.
> 
> Commit 35198e323001 fixed the same issue in ioc_qos_prfill() and
> ioc_cost_model_prfill() by adding spin_lock_irq(&ioc->lock).  However,
> those functions read configuration parameters (qos/model) that need
> synchronized reads.  In contrast, ioc_pd_stat() only reads stat
> values (vrate, usage) where stale reads are harmless, so data_race()
> is more appropriate — it silences the KCSAN warning without adding
> lock contention during high-frequency stat reads.
> 
> Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>

Acked-by: Tejun Heo <tj@xxxxxxxxxx>

Thanks.

-- 
tejun