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Message-Id: <20250815080216.410665-9-yukuai1@huaweicloud.com>
Date: Fri, 15 Aug 2025 16:02:14 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
hare@...e.de,
nilay@...ux.ibm.com,
ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org,
yukuai3@...wei.com,
yukuai1@...weicloud.com,
yi.zhang@...wei.com,
yangerkun@...wei.com,
johnny.chenyi@...wei.com
Subject: [PATCH 08/10] blk-mq: fix blk_mq_tags double free while nr_requests grown
From: Yu Kuai <yukuai3@...wei.com>
In the case user trigger tags grow by queue sysfs attribute nr_requests,
hctx->sched_tags will be freed directly and replaced with a new
allocated tags, see blk_mq_tag_update_depth().
The problem is that hctx->sched_tags is from elevator->et->tags, while
et->tags is still the freed tags, hence later elevator exist will try to
free the tags again, causing kernel panic.
Fix this problem by using new allocated elevator_tags, also convert
blk_mq_update_nr_requests to void since this helper will never fail now.
Meanwhile, there is a longterm problem can be fixed as well:
If blk_mq_tag_update_depth() succeed for previous hctx, then bitmap depth
is updated, however, if following hctx failed, q->nr_requests is not
updated and the previous hctx->sched_tags endup bigger than q->nr_requests.
Fixes: f5a6604f7a44 ("block: fix lockdep warning caused by lock dependency in elv_iosched_store")
Fixes: e3a2b3f931f5 ("blk-mq: allow changing of queue depth through sysfs")
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
block/blk-mq.c | 19 ++++++-------------
block/blk-mq.h | 4 +++-
block/blk-sysfs.c | 21 ++++++++++++++-------
3 files changed, 23 insertions(+), 21 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 11c8baebb9a0..e9f037a25fe3 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4917,12 +4917,12 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
}
EXPORT_SYMBOL(blk_mq_free_tag_set);
-int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
+void blk_mq_update_nr_requests(struct request_queue *q,
+ struct elevator_tags *et, unsigned int nr)
{
struct blk_mq_tag_set *set = q->tag_set;
struct blk_mq_hw_ctx *hctx;
unsigned long i;
- int ret = 0;
blk_mq_quiesce_queue(q);
@@ -4946,24 +4946,17 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
nr - hctx->sched_tags->nr_reserved_tags);
}
} else {
- queue_for_each_hw_ctx(q, hctx, i) {
- if (!hctx->tags)
- continue;
- ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
- nr);
- if (ret)
- goto out;
- }
+ blk_mq_free_sched_tags(q->elevator->et, set);
+ queue_for_each_hw_ctx(q, hctx, i)
+ hctx->sched_tags = et->tags[i];
+ q->elevator->et = et;
}
q->nr_requests = nr;
if (q->elevator && q->elevator->type->ops.depth_updated)
q->elevator->type->ops.depth_updated(q);
-out:
blk_mq_unquiesce_queue(q);
-
- return ret;
}
/*
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 731f4578d9a8..98740f9c204e 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -6,6 +6,7 @@
#include "blk-stat.h"
struct blk_mq_tag_set;
+struct elevator_tags;
struct blk_mq_ctxs {
struct kobject kobj;
@@ -45,7 +46,8 @@ void blk_mq_submit_bio(struct bio *bio);
int blk_mq_poll(struct request_queue *q, blk_qc_t cookie, struct io_comp_batch *iob,
unsigned int flags);
void blk_mq_exit_queue(struct request_queue *q);
-int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
+void blk_mq_update_nr_requests(struct request_queue *q,
+ struct elevator_tags *et, unsigned int nr);
void blk_mq_wake_waiters(struct request_queue *q);
bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *,
bool);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 37eae7927b45..848648456255 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -64,11 +64,12 @@ static ssize_t queue_requests_show(struct gendisk *disk, char *page)
static ssize_t
queue_requests_store(struct gendisk *disk, const char *page, size_t count)
{
- unsigned long nr;
- int ret, err;
- unsigned int memflags;
struct request_queue *q = disk->queue;
struct blk_mq_tag_set *set = q->tag_set;
+ struct elevator_tags *et = NULL;
+ unsigned int memflags;
+ unsigned long nr;
+ int ret;
ret = queue_var_store(&nr, page, count);
if (ret < 0)
@@ -90,12 +91,18 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count)
goto unlock;
}
+ if (q->elevator && nr > q->elevator->et->nr_requests) {
+ /* allocate memory before freezing queue to prevent deadlock */
+ et = blk_mq_alloc_sched_tags(set, q->nr_hw_queues, nr);
+ if (!et) {
+ ret = -ENOMEM;
+ goto unlock;
+ }
+ }
+
memflags = blk_mq_freeze_queue(q);
mutex_lock(&q->elevator_lock);
- err = blk_mq_update_nr_requests(disk->queue, nr);
- if (err)
- ret = err;
-
+ blk_mq_update_nr_requests(disk->queue, et, nr);
mutex_unlock(&q->elevator_lock);
blk_mq_unfreeze_queue(q, memflags);
--
2.39.2
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