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.
cpu hotplug handling for blk-mq (blk_mq_queue_reinit) does unregister
and register sysfs entries of hctx for all request queues in
all_q_list. On the other hand, these entries for a request queue may
have already been unregistered when cpu hotplug event occurs. Because
those sysfs entries are unregistered by blk_mq_unregister_disk()
firstly, and then a request queue is deleted from all_q_list by
blk_mq_free_queue(). So there is a race window that cpu hotplug must
not occur.
Fix it by serializing sysfs registration/unregistration with using
per hardware queue mutex and BLK_MQ_F_SYSFS_UP flag.
Signed-off-by: Akinobu Mita <akinobu.m...@gmail.com>
Cc: Jens Axboe <ax...@kernel.dk>
---
block/blk-mq-sysfs.c | 19 +++++++++++++++++--
block/blk-mq.c | 1 +
include/linux/blk-mq.h | 1 +
3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index b79685e..d8ef3a3 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -371,7 +371,10 @@ void blk_mq_unregister_disk(struct gendisk *disk)
int i, j;
queue_for_each_hw_ctx(q, hctx, i) {
+ mutex_lock(&hctx->sysfs_up_lock);
blk_mq_unregister_hctx(hctx);
+ hctx->flags &= ~BLK_MQ_F_SYSFS_UP;
+ mutex_unlock(&hctx->sysfs_up_lock);
hctx_for_each_ctx(hctx, ctx, j)
kobject_put(&ctx->kobj);
@@ -423,10 +426,17 @@ int blk_mq_register_disk(struct gendisk *disk)
kobject_uevent(&q->mq_kobj, KOBJ_ADD);
queue_for_each_hw_ctx(q, hctx, i) {
+ mutex_lock(&hctx->sysfs_up_lock);
+
hctx->flags |= BLK_MQ_F_SYSFS_UP;
ret = blk_mq_register_hctx(hctx);
- if (ret)
+
+ if (ret) {
+ hctx->flags &= ~BLK_MQ_F_SYSFS_UP;
+ mutex_unlock(&hctx->sysfs_up_lock);
break;
+ }
+ mutex_unlock(&hctx->sysfs_up_lock);
}
if (ret) {
@@ -443,8 +453,11 @@ void blk_mq_sysfs_unregister(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;
- queue_for_each_hw_ctx(q, hctx, i)
+ queue_for_each_hw_ctx(q, hctx, i) {
+ mutex_lock(&hctx->sysfs_up_lock);
blk_mq_unregister_hctx(hctx);
+ mutex_unlock(&hctx->sysfs_up_lock);
+ }
}
int blk_mq_sysfs_register(struct request_queue *q)
@@ -453,7 +466,9 @@ int blk_mq_sysfs_register(struct request_queue *q)
int i, ret = 0;
queue_for_each_hw_ctx(q, hctx, i) {
+ mutex_lock(&hctx->sysfs_up_lock);
ret = blk_mq_register_hctx(hctx);
+ mutex_unlock(&hctx->sysfs_up_lock);
if (ret)
break;
}
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 594eea0..ec94258 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1660,6 +1660,7 @@ static int blk_mq_init_hctx(struct request_queue *q,
INIT_DELAYED_WORK(&hctx->delay_work, blk_mq_delay_work_fn);
spin_lock_init(&hctx->lock);
INIT_LIST_HEAD(&hctx->dispatch);
+ mutex_init(&hctx->sysfs_up_lock);
hctx->queue = q;
hctx->queue_num = hctx_idx;
hctx->flags = set->flags;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 2056a99..78cd4f3 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -59,6 +59,7 @@ struct blk_mq_hw_ctx {
struct blk_mq_cpu_notifier cpu_notifier;
struct kobject kobj;
+ struct mutex sysfs_up_lock;
};
struct blk_mq_tag_set {
--
1.9.1
--
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