| Message ID | 20190821091506.21196-4-ming.lei@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: don't acquire .sysfs_lock before removing mq & iosched kobjects | expand |
On 8/21/19 2:15 AM, Ming Lei wrote: > blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue() > and blk_mq_update_nr_hw_queues(). For the former caller, the kobject > isn't exposed to userspace yet. For the latter caller, sysfs/debugfs > is un-registered before updating nr_hw_queues. > > On the other hand, commit 2f8f1336a48b ("blk-mq: always free hctx after > request queue is freed") moves freeing hctx into queue's release > handler, so there won't be race with queue release path too. > > So don't hold q->sysfs_lock in blk_mq_map_swqueue(). > > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Hannes Reinecke <hare@suse.com> > Cc: Greg KH <gregkh@linuxfoundation.org> > Cc: Mike Snitzer <snitzer@redhat.com> > Cc: Bart Van Assche <bvanassche@acm.org> > Signed-off-by: Ming Lei <ming.lei@redhat.com> > --- > block/blk-mq.c | 7 ------- > 1 file changed, 7 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 6968de9d7402..b0ee0cac737f 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2456,11 +2456,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) > struct blk_mq_ctx *ctx; > struct blk_mq_tag_set *set = q->tag_set; > > - /* > - * Avoid others reading imcomplete hctx->cpumask through sysfs > - */ > - mutex_lock(&q->sysfs_lock); > - > queue_for_each_hw_ctx(q, hctx, i) { > cpumask_clear(hctx->cpumask); > hctx->nr_ctx = 0; > @@ -2521,8 +2516,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) > HCTX_TYPE_DEFAULT, i); > } > > - mutex_unlock(&q->sysfs_lock); > - > queue_for_each_hw_ctx(q, hctx, i) { > /* > * If no software queues are mapped to this hardware queue, > How about adding WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) ? Anyway: Reviewed-by: Bart Van Assche <bvanassche@acm.org>
On Wed, Aug 21, 2019 at 08:53:52AM -0700, Bart Van Assche wrote: > On 8/21/19 2:15 AM, Ming Lei wrote: > > blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue() > > and blk_mq_update_nr_hw_queues(). For the former caller, the kobject > > isn't exposed to userspace yet. For the latter caller, sysfs/debugfs > > is un-registered before updating nr_hw_queues. > > > > On the other hand, commit 2f8f1336a48b ("blk-mq: always free hctx after > > request queue is freed") moves freeing hctx into queue's release > > handler, so there won't be race with queue release path too. > > > > So don't hold q->sysfs_lock in blk_mq_map_swqueue(). > > > > Cc: Christoph Hellwig <hch@infradead.org> > > Cc: Hannes Reinecke <hare@suse.com> > > Cc: Greg KH <gregkh@linuxfoundation.org> > > Cc: Mike Snitzer <snitzer@redhat.com> > > Cc: Bart Van Assche <bvanassche@acm.org> > > Signed-off-by: Ming Lei <ming.lei@redhat.com> > > --- > > block/blk-mq.c | 7 ------- > > 1 file changed, 7 deletions(-) > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index 6968de9d7402..b0ee0cac737f 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -2456,11 +2456,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) > > struct blk_mq_ctx *ctx; > > struct blk_mq_tag_set *set = q->tag_set; > > - /* > > - * Avoid others reading imcomplete hctx->cpumask through sysfs > > - */ > > - mutex_lock(&q->sysfs_lock); > > - > > queue_for_each_hw_ctx(q, hctx, i) { > > cpumask_clear(hctx->cpumask); > > hctx->nr_ctx = 0; > > @@ -2521,8 +2516,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) > > HCTX_TYPE_DEFAULT, i); > > } > > - mutex_unlock(&q->sysfs_lock); > > - > > queue_for_each_hw_ctx(q, hctx, i) { > > /* > > * If no software queues are mapped to this hardware queue, > > > > How about adding WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, > &q->queue_flags)) ? q->kobject isn't un-registered before updating nr_hw_queues, and only hctx->kobj is un-registered, so we can't add the warn here. Thanks, Ming
diff --git a/block/blk-mq.c b/block/blk-mq.c index 6968de9d7402..b0ee0cac737f 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2456,11 +2456,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) struct blk_mq_ctx *ctx; struct blk_mq_tag_set *set = q->tag_set; - /* - * Avoid others reading imcomplete hctx->cpumask through sysfs - */ - mutex_lock(&q->sysfs_lock); - queue_for_each_hw_ctx(q, hctx, i) { cpumask_clear(hctx->cpumask); hctx->nr_ctx = 0; @@ -2521,8 +2516,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) HCTX_TYPE_DEFAULT, i); } - mutex_unlock(&q->sysfs_lock); - queue_for_each_hw_ctx(q, hctx, i) { /* * If no software queues are mapped to this hardware queue,
blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue() and blk_mq_update_nr_hw_queues(). For the former caller, the kobject isn't exposed to userspace yet. For the latter caller, sysfs/debugfs is un-registered before updating nr_hw_queues. On the other hand, commit 2f8f1336a48b ("blk-mq: always free hctx after request queue is freed") moves freeing hctx into queue's release handler, so there won't be race with queue release path too. So don't hold q->sysfs_lock in blk_mq_map_swqueue(). Cc: Christoph Hellwig <hch@infradead.org> Cc: Hannes Reinecke <hare@suse.com> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: Mike Snitzer <snitzer@redhat.com> Cc: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Ming Lei <ming.lei@redhat.com> --- block/blk-mq.c | 7 ------- 1 file changed, 7 deletions(-)