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blk-mq: fallback to previous nr_hw_queues when updating fails

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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>
This commit is contained in:
Jianchao Wang 2018-10-12 18:07:28 +08:00 committed by Jens Axboe
parent 34d11ffac1
commit e01ad46d53
1 changed files with 24 additions and 3 deletions
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27
block/blk-mq.c
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@ -2557,7 +2557,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
struct request_queue *q)
{
int i, j;
int i, j, end;
struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;
/* protect against switching io scheduler */
@ -2591,8 +2591,20 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
break;
}
}
/*
* Increasing nr_hw_queues fails. Free the newly allocated
* hctxs and keep the previous q->nr_hw_queues.
*/
if (i != set->nr_hw_queues) {
j = q->nr_hw_queues;
end = i;
} else {
j = i;
end = q->nr_hw_queues;
q->nr_hw_queues = set->nr_hw_queues;
}
for (j = i; j < q->nr_hw_queues; j++) {
for (; j < end; j++) {
struct blk_mq_hw_ctx *hctx = hctxs[j];
if (hctx) {
@ -2604,7 +2616,6 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
}
}
q->nr_hw_queues = i;
mutex_unlock(&q->sysfs_lock);
}
@ -2989,6 +3000,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
{
struct request_queue *q;
LIST_HEAD(head);
int prev_nr_hw_queues;
lockdep_assert_held(&set->tag_list_lock);
@ -3017,10 +3029,19 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
blk_mq_sysfs_unregister(q);
}
prev_nr_hw_queues = set->nr_hw_queues;
set->nr_hw_queues = nr_hw_queues;
blk_mq_update_queue_map(set);
fallback:
list_for_each_entry(q, &set->tag_list, tag_set_list) {
blk_mq_realloc_hw_ctxs(set, q);
if (q->nr_hw_queues != set->nr_hw_queues) {
pr_warn("Increasing nr_hw_queues to %d fails, fallback to %d\n",
nr_hw_queues, prev_nr_hw_queues);
set->nr_hw_queues = prev_nr_hw_queues;
blk_mq_map_queues(set);
goto fallback;
}
blk_mq_map_swqueue(q);
}