Re: [PATCH 4/8] block: improve disk_zone_wplug_schedule_bio_work()

[Bart Van Assche <bvanassche@acm.org>]

On 2/23/26 3:59 AM, Hannes Reinecke wrote:
> On 2/21/26 01:44, Damien Le Moal wrote:
>>       WARN_ON_ONCE(!(zwplug->flags & BLK_ZONE_WPLUG_PLUGGED));
>> -    refcount_inc(&zwplug->ref);
>> -    queue_work(disk->zone_wplugs_wq, &zwplug->bio_work);
>> +    if (queue_work(disk->zone_wplugs_wq, &zwplug->bio_work))
>> +        refcount_inc(&zwplug->ref);
>>   }
>>   static inline void disk_zone_wplug_add_bio(struct gendisk *disk,
> 
> Urgh. Don't.
> There is a race condition; 'bio_work' might be scheduled directly and
> complete before 'refcount_inc()' is called.
> You have to invert the statement by keeping the 'refcount_inc()'
> before calling 'queue_work()', and then drop the reference again
> if queue_work failed.

Hi Hannes,

I think that the above code is fine because the caller holds
zwplug->lock. blk_zone_wplug_bio_work() only decrements zwplug->ref
after it has locked and unlocked the same lock.

Bart.