| Message ID | 20180112160352.GA6270@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Jan 12, 2018 at 11:03:52AM -0500, Mike Snitzer wrote: > The original commit e9a823fb34a8b (block: fix warning when I/O elevator > is changed as request_queue is being removed) is pretty conflated. > "conflated" because the resource being protected by q->sysfs_lock isn't > the queue_flags (it is the 'queue' kobj). > > q->sysfs_lock serializes __elevator_change() (via elv_iosched_store) > from racing with blk_unregister_queue(): > 1) By holding q->sysfs_lock first, __elevator_change() can complete > before a racing blk_unregister_queue(). > 2) Conversely, __elevator_change() is testing for QUEUE_FLAG_REGISTERED > in case elv_iosched_store() loses the race with blk_unregister_queue(), > it needs a way to know the 'queue' kobj isn't there. > > Expand the scope of blk_unregister_queue()'s q->sysfs_lock use so it is > held until after the 'queue' kobj is removed. > > To do so blk_mq_unregister_dev() must not also take q->sysfs_lock. So > rename __blk_mq_unregister_dev() to blk_mq_unregister_dev(). > > Also, blk_unregister_queue() should use q->queue_lock to protect against > any concurrent writes to q->queue_flags -- even though chances are the > queue is being cleaned up so no concurrent writes are likely. > > Fixes: e9a823fb34a8b ("block: fix warning when I/O elevator is changed as request_queue is being removed") > Signed-off-by: Mike Snitzer <snitzer@redhat.com> > --- > block/blk-mq-sysfs.c | 9 +-------- > block/blk-sysfs.c | 13 ++++++++++--- > 2 files changed, 11 insertions(+), 11 deletions(-) > > v6: blk_mq_unregister_dev now requires q->sysfs_lock be held, Ming: I am > not seeing any lockdep complaints with this. I've tested bio-based, > blk-mq and old .request_fn request-based. > > diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c > index 79969c3c234f..a54b4b070f1c 100644 > --- a/block/blk-mq-sysfs.c > +++ b/block/blk-mq-sysfs.c > @@ -248,7 +248,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx) > return ret; > } > > -static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q) > +void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) > { > struct blk_mq_hw_ctx *hctx; > int i; > @@ -265,13 +265,6 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q) > q->mq_sysfs_init_done = false; > } > > -void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) > -{ > - mutex_lock(&q->sysfs_lock); > - __blk_mq_unregister_dev(dev, q); > - mutex_unlock(&q->sysfs_lock); > -} > - > void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx) > { > kobject_init(&hctx->kobj, &blk_mq_hw_ktype); > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index 870484eaed1f..9272452ff456 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -929,12 +929,17 @@ void blk_unregister_queue(struct gendisk *disk) > if (WARN_ON(!q)) > return; > > + /* > + * Protect against the 'queue' kobj being accessed > + * while/after it is removed. > + */ > mutex_lock(&q->sysfs_lock); > - queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q); > - mutex_unlock(&q->sysfs_lock); > > - wbt_exit(q); > + spin_lock_irq(q->queue_lock); > + queue_flag_clear(QUEUE_FLAG_REGISTERED, q); > + spin_unlock_irq(q->queue_lock); > > + wbt_exit(q); > > if (q->mq_ops) > blk_mq_unregister_dev(disk_to_dev(disk), q); > @@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk) > kobject_del(&q->kobj); > blk_trace_remove_sysfs(disk_to_dev(disk)); > kobject_put(&disk_to_dev(disk)->kobj); > + > + mutex_unlock(&q->sysfs_lock); > } Reviewed-by: Ming Lei <ming.lei@redhat.com>
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index 79969c3c234f..a54b4b070f1c 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -248,7 +248,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx) return ret; } -static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q) +void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) { struct blk_mq_hw_ctx *hctx; int i; @@ -265,13 +265,6 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q) q->mq_sysfs_init_done = false; } -void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) -{ - mutex_lock(&q->sysfs_lock); - __blk_mq_unregister_dev(dev, q); - mutex_unlock(&q->sysfs_lock); -} - void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx) { kobject_init(&hctx->kobj, &blk_mq_hw_ktype); diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 870484eaed1f..9272452ff456 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -929,12 +929,17 @@ void blk_unregister_queue(struct gendisk *disk) if (WARN_ON(!q)) return; + /* + * Protect against the 'queue' kobj being accessed + * while/after it is removed. + */ mutex_lock(&q->sysfs_lock); - queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q); - mutex_unlock(&q->sysfs_lock); - wbt_exit(q); + spin_lock_irq(q->queue_lock); + queue_flag_clear(QUEUE_FLAG_REGISTERED, q); + spin_unlock_irq(q->queue_lock); + wbt_exit(q); if (q->mq_ops) blk_mq_unregister_dev(disk_to_dev(disk), q); @@ -946,4 +951,6 @@ void blk_unregister_queue(struct gendisk *disk) kobject_del(&q->kobj); blk_trace_remove_sysfs(disk_to_dev(disk)); kobject_put(&disk_to_dev(disk)->kobj); + + mutex_unlock(&q->sysfs_lock); }
The original commit e9a823fb34a8b (block: fix warning when I/O elevator is changed as request_queue is being removed) is pretty conflated. "conflated" because the resource being protected by q->sysfs_lock isn't the queue_flags (it is the 'queue' kobj). q->sysfs_lock serializes __elevator_change() (via elv_iosched_store) from racing with blk_unregister_queue(): 1) By holding q->sysfs_lock first, __elevator_change() can complete before a racing blk_unregister_queue(). 2) Conversely, __elevator_change() is testing for QUEUE_FLAG_REGISTERED in case elv_iosched_store() loses the race with blk_unregister_queue(), it needs a way to know the 'queue' kobj isn't there. Expand the scope of blk_unregister_queue()'s q->sysfs_lock use so it is held until after the 'queue' kobj is removed. To do so blk_mq_unregister_dev() must not also take q->sysfs_lock. So rename __blk_mq_unregister_dev() to blk_mq_unregister_dev(). Also, blk_unregister_queue() should use q->queue_lock to protect against any concurrent writes to q->queue_flags -- even though chances are the queue is being cleaned up so no concurrent writes are likely. Fixes: e9a823fb34a8b ("block: fix warning when I/O elevator is changed as request_queue is being removed") Signed-off-by: Mike Snitzer <snitzer@redhat.com> --- block/blk-mq-sysfs.c | 9 +-------- block/blk-sysfs.c | 13 ++++++++++--- 2 files changed, 11 insertions(+), 11 deletions(-) v6: blk_mq_unregister_dev now requires q->sysfs_lock be held, Ming: I am not seeing any lockdep complaints with this. I've tested bio-based, blk-mq and old .request_fn request-based.