blk-mq: fix sysfs registration/unregistration race

There is a race between cpu hotplug handling and adding/deleting
gendisk for blk-mq, where both are trying to register and unregister
the same sysfs entries.

null_add_dev
    --> blk_mq_init_queue
        --> blk_mq_init_allocated_queue
            --> add to 'all_q_list' (*)
    --> add_disk
        --> blk_register_queue
            --> blk_mq_register_disk (++)

null_del_dev
    --> del_gendisk
        --> blk_unregister_queue
            --> blk_mq_unregister_disk (--)
    --> blk_cleanup_queue
        --> blk_mq_free_queue
            --> del from 'all_q_list' (*)

blk_mq_queue_reinit
    --> blk_mq_sysfs_unregister (-)
    --> blk_mq_sysfs_register (+)

While the request queue is added to 'all_q_list' (*),
blk_mq_queue_reinit() can be called for the queue anytime by CPU
hotplug callback.  But blk_mq_sysfs_unregister (-) and
blk_mq_sysfs_register (+) in blk_mq_queue_reinit must not be called
before blk_mq_register_disk (++) and after blk_mq_unregister_disk (--)
is finished.  Because '/sys/block/*/mq/' is not exists.

There has already been BLK_MQ_F_SYSFS_UP flag in hctx->flags which can
be used to track these sysfs stuff, but it is only fixing this issue
partially.

In order to fix it completely, we just need per-queue flag instead of
per-hctx flag with appropriate locking.  So this introduces
q->mq_sysfs_init_done which is properly protected with all_q_mutex.

Also, we need to ensure that blk_mq_map_swqueue() is called with
all_q_mutex is held.  Since hctx->nr_ctx is reset temporarily and
updated in blk_mq_map_swqueue(), so we should avoid
blk_mq_register_hctx() seeing the temporary hctx->nr_ctx value
in CPU hotplug handling or adding/deleting gendisk .

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Akinobu Mita 2015-09-27 02:09:20 +09:00 committed by Jens Axboe
parent 1356aae083
commit 4593fdbe7a
4 changed files with 27 additions and 12 deletions

View File

@ -343,7 +343,7 @@ static void blk_mq_unregister_hctx(struct blk_mq_hw_ctx *hctx)
struct blk_mq_ctx *ctx;
int i;
if (!hctx->nr_ctx || !(hctx->flags & BLK_MQ_F_SYSFS_UP))
if (!hctx->nr_ctx)
return;
hctx_for_each_ctx(hctx, ctx, i)
@ -358,7 +358,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
struct blk_mq_ctx *ctx;
int i, ret;
if (!hctx->nr_ctx || !(hctx->flags & BLK_MQ_F_SYSFS_UP))
if (!hctx->nr_ctx)
return 0;
ret = kobject_add(&hctx->kobj, &q->mq_kobj, "%u", hctx->queue_num);
@ -381,6 +381,8 @@ void blk_mq_unregister_disk(struct gendisk *disk)
struct blk_mq_ctx *ctx;
int i, j;
blk_mq_disable_hotplug();
queue_for_each_hw_ctx(q, hctx, i) {
blk_mq_unregister_hctx(hctx);
@ -395,6 +397,9 @@ void blk_mq_unregister_disk(struct gendisk *disk)
kobject_put(&q->mq_kobj);
kobject_put(&disk_to_dev(disk)->kobj);
q->mq_sysfs_init_done = false;
blk_mq_enable_hotplug();
}
static void blk_mq_sysfs_init(struct request_queue *q)
@ -425,27 +430,30 @@ int blk_mq_register_disk(struct gendisk *disk)
struct blk_mq_hw_ctx *hctx;
int ret, i;
blk_mq_disable_hotplug();
blk_mq_sysfs_init(q);
ret = kobject_add(&q->mq_kobj, kobject_get(&dev->kobj), "%s", "mq");
if (ret < 0)
return ret;
goto out;
kobject_uevent(&q->mq_kobj, KOBJ_ADD);
queue_for_each_hw_ctx(q, hctx, i) {
hctx->flags |= BLK_MQ_F_SYSFS_UP;
ret = blk_mq_register_hctx(hctx);
if (ret)
break;
}
if (ret) {
if (ret)
blk_mq_unregister_disk(disk);
return ret;
}
else
q->mq_sysfs_init_done = true;
out:
blk_mq_enable_hotplug();
return 0;
return ret;
}
EXPORT_SYMBOL_GPL(blk_mq_register_disk);
@ -454,6 +462,9 @@ void blk_mq_sysfs_unregister(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;
if (!q->mq_sysfs_init_done)
return;
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_unregister_hctx(hctx);
}
@ -463,6 +474,9 @@ int blk_mq_sysfs_register(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i, ret = 0;
if (!q->mq_sysfs_init_done)
return ret;
queue_for_each_hw_ctx(q, hctx, i) {
ret = blk_mq_register_hctx(hctx);
if (ret)

View File

@ -2035,13 +2035,13 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
goto err_hctxs;
mutex_lock(&all_q_mutex);
list_add_tail(&q->all_q_node, &all_q_list);
mutex_unlock(&all_q_mutex);
blk_mq_add_queue_tag_set(set, q);
blk_mq_map_swqueue(q);
mutex_unlock(&all_q_mutex);
return q;
err_hctxs:

View File

@ -145,7 +145,6 @@ enum {
BLK_MQ_F_SHOULD_MERGE = 1 << 0,
BLK_MQ_F_TAG_SHARED = 1 << 1,
BLK_MQ_F_SG_MERGE = 1 << 2,
BLK_MQ_F_SYSFS_UP = 1 << 3,
BLK_MQ_F_DEFER_ISSUE = 1 << 4,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
BLK_MQ_F_ALLOC_POLICY_BITS = 1,

View File

@ -456,6 +456,8 @@ struct request_queue {
struct blk_mq_tag_set *tag_set;
struct list_head tag_set_list;
struct bio_set *bio_split;
bool mq_sysfs_init_done;
};
#define QUEUE_FLAG_QUEUED 1 /* uses generic tag queueing */