Messages in this thread Patch in this message | | | From | Akinobu Mita <> | Subject | [PATCH 1/4] blk-mq: fix sysfs registration/unregistration race | Date | Sun, 21 Jun 2015 22:52:28 +0900 |
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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.mita@gmail.com> Cc: Jens Axboe <axboe@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
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