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block: validate QoS before calling __rq_qos_done_bio()

If a bio has BIO_QOS_xxx set, it doesn't guarantee that q->rq_qos is
also present at-least for stacked block devices. For instance, in case
of NVMe when multipath is enabled, the bottom device may have QoS
enabled but top device doesn't. So always validate QoS is enabled and
q->rq_qos is present before calling __rq_qos_done_bio().

Fixes: 370ac285f23a ("block: avoid cpu_hotplug_lock depedency on freeze_lock")
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/all/3a07b752-06a4-4eee-b302-f4669feb859d@linux.ibm.com/
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250826163128.1952394-1-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

authored by

Nilay Shroff and committed by
Jens Axboe e3ef9445 198f36f9

+8 -5
+8 -5
block/blk-rq-qos.h
··· 149 149 q = bdev_get_queue(bio->bi_bdev); 150 150 151 151 /* 152 - * If a bio has BIO_QOS_xxx set, it implicitly implies that 153 - * q->rq_qos is present. So, we skip re-checking q->rq_qos 154 - * here as an extra optimization and directly call 155 - * __rq_qos_done_bio(). 152 + * A BIO may carry BIO_QOS_* flags even if the associated request_queue 153 + * does not have rq_qos enabled. This can happen with stacked block 154 + * devices — for example, NVMe multipath, where it's possible that the 155 + * bottom device has QoS enabled but the top device does not. Therefore, 156 + * always verify that q->rq_qos is present and QoS is enabled before 157 + * calling __rq_qos_done_bio(). 156 158 */ 157 - __rq_qos_done_bio(q->rq_qos, bio); 159 + if (test_bit(QUEUE_FLAG_QOS_ENABLED, &q->queue_flags) && q->rq_qos) 160 + __rq_qos_done_bio(q->rq_qos, bio); 158 161 } 159 162 160 163 static inline void rq_qos_throttle(struct request_queue *q, struct bio *bio)