From 4593fdbe7a2f44d5e64c627c715dd0bcec9bdf14 Mon Sep 17 00:00:00 2001 From: Akinobu Mita Date: Sun, 27 Sep 2015 02:09:20 +0900 Subject: 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 Reviewed-by: Ming Lei Cc: Ming Lei Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- block/blk-mq-sysfs.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) (limited to 'block/blk-mq-sysfs.c') diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index 279c5d674edf..189f5ae6522a 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -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) -- cgit v1.2.3