blk-mq: fallback to previous nr_hw_queues when updating fails
When we try to increate the nr_hw_queues, we may fail due to shortage of memory or other reason, then blk_mq_realloc_hw_ctxs stops and some entries in q->queue_hw_ctx are left with NULL. However, because queue map has been updated with new nr_hw_queues, some cpus have been mapped to hw queue which just encounters allocation failure, thus blk_mq_map_queue could return NULL. This will cause panic in following blk_mq_map_swqueue. To fix it, when increase nr_hw_queues fails, fallback to previous nr_hw_queues and post warning. At the same time, driver's .map_queues usually use completion irq affinity to map hw and cpu, fallback nr_hw_queues will cause lack of some cpu's map to hw, so use default blk_mq_map_queues to do that. Reported-by: syzbot+83e8cbe702263932d9d4@syzkaller.appspotmail.com Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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@ -2557,7 +2557,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
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static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
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struct request_queue *q)
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{
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int i, j;
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int i, j, end;
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struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;
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/* protect against switching io scheduler */
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@ -2591,8 +2591,20 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
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break;
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}
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}
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/*
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* Increasing nr_hw_queues fails. Free the newly allocated
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* hctxs and keep the previous q->nr_hw_queues.
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*/
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if (i != set->nr_hw_queues) {
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j = q->nr_hw_queues;
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end = i;
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} else {
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j = i;
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end = q->nr_hw_queues;
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q->nr_hw_queues = set->nr_hw_queues;
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}
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for (j = i; j < q->nr_hw_queues; j++) {
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for (; j < end; j++) {
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struct blk_mq_hw_ctx *hctx = hctxs[j];
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if (hctx) {
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@ -2604,7 +2616,6 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
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}
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}
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q->nr_hw_queues = i;
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mutex_unlock(&q->sysfs_lock);
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}
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@ -2989,6 +3000,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
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{
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struct request_queue *q;
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LIST_HEAD(head);
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int prev_nr_hw_queues;
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lockdep_assert_held(&set->tag_list_lock);
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@ -3017,10 +3029,19 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
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blk_mq_sysfs_unregister(q);
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}
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prev_nr_hw_queues = set->nr_hw_queues;
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set->nr_hw_queues = nr_hw_queues;
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blk_mq_update_queue_map(set);
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fallback:
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list_for_each_entry(q, &set->tag_list, tag_set_list) {
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blk_mq_realloc_hw_ctxs(set, q);
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if (q->nr_hw_queues != set->nr_hw_queues) {
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pr_warn("Increasing nr_hw_queues to %d fails, fallback to %d\n",
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nr_hw_queues, prev_nr_hw_queues);
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set->nr_hw_queues = prev_nr_hw_queues;
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blk_mq_map_queues(set);
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goto fallback;
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}
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blk_mq_map_swqueue(q);
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}
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