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block: fix module reference leak in mq-deadline I/O scheduler 

During probe, when the block layer registers a request queue, it
defaults to the mq-deadline I/O scheduler if the device is single-queue
and the mq-deadline module is available. To determine availability, the
elevator_set_default() invokes elevator_find_get(), which increments the
module's reference count. However, this reference is never released,
resulting in a module reference leak that prevents the mq-deadline module
from being unloaded.

This patch fixes the issue by ensuring the acquired module reference is
properly released.

Fixes: 1e44bedbc9 ("block: unifying elevator change")
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250719132722.769536-1-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Nilay Shroff 2025-07-19 18:56:47 +05:30 committed by Jens Axboe
parent 2680efde75
commit 1966554b2e
1 changed files with 13 additions and 6 deletions
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17
block/elevator.c
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@ -719,7 +719,8 @@ void elevator_set_default(struct request_queue *q)
.name = "mq-deadline", .name = "mq-deadline",
.no_uevent = true, .no_uevent = true,
}; };
int err = 0; int err;
struct elevator_type *e;
/* now we allow to switch elevator */ /* now we allow to switch elevator */
blk_queue_flag_clear(QUEUE_FLAG_NO_ELV_SWITCH, q); blk_queue_flag_clear(QUEUE_FLAG_NO_ELV_SWITCH, q);
@ -732,12 +733,18 @@ void elevator_set_default(struct request_queue *q)
* have multiple queues or mq-deadline is not available, default * have multiple queues or mq-deadline is not available, default
* to "none". * to "none".
*/ */
if (elevator_find_get(ctx.name) && (q->nr_hw_queues == 1 || e = elevator_find_get(ctx.name);
blk_mq_is_shared_tags(q->tag_set->flags))) if (!e)
return;
if ((q->nr_hw_queues == 1 ||
blk_mq_is_shared_tags(q->tag_set->flags))) {
err = elevator_change(q, &ctx); err = elevator_change(q, &ctx);
if (err < 0) if (err < 0)
pr_warn("\"%s\" elevator initialization, failed %d, " pr_warn("\"%s\" elevator initialization, failed %d, falling back to \"none\"\n",
"falling back to \"none\"\n", ctx.name, err); ctx.name, err);
}
elevator_put(e);
} }
void elevator_set_none(struct request_queue *q) void elevator_set_none(struct request_queue *q)