updating nr_hw_queues is usually used for error handling code, when it doesn't make sense to allow blk-mq elevator switching, since nr_hw_queues may change, and elevator tags depends on nr_hw_queues. Prevent elevator switch during updating nr_hw_queues by setting flag of BLK_MQ_F_UPDATE_HW_QUEUES, and use srcu to fail elevator switch during the period. Here elevator switch code is srcu reader of nr_hw_queues, and blk_mq_update_nr_hw_queues() is the writer. This way avoids lot of trouble. Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx> Closes: https://lore.kernel.org/linux-block/mz4t4tlwiqjijw3zvqnjb7ovvvaegkqganegmmlc567tt5xj67@xal5ro544cnc/ Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- block/blk-mq-debugfs.c | 1 + block/blk-mq.c | 19 ++++++++++++++++++- block/elevator.c | 12 +++++++++++- include/linux/blk-mq.h | 10 +++++++++- 4 files changed, 39 insertions(+), 3 deletions(-) diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c index c308699ded58..27f984311bb7 100644 --- a/block/blk-mq-debugfs.c +++ b/block/blk-mq-debugfs.c @@ -180,6 +180,7 @@ static const char *const hctx_flag_name[] = { HCTX_FLAG_NAME(BLOCKING), HCTX_FLAG_NAME(TAG_RR), HCTX_FLAG_NAME(NO_SCHED_BY_DEFAULT), + HCTX_FLAG_NAME(UPDATE_HW_QUEUES), }; #undef HCTX_FLAG_NAME diff --git a/block/blk-mq.c b/block/blk-mq.c index d7a103dc258b..4b0707fb7ae3 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -4785,12 +4785,16 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set) goto out_free_srcu; } + ret = init_srcu_struct(&set->update_nr_hwq_srcu); + if (ret) + goto out_cleanup_srcu; + ret = -ENOMEM; set->tags = kcalloc_node(set->nr_hw_queues, sizeof(struct blk_mq_tags *), GFP_KERNEL, set->numa_node); if (!set->tags) - goto out_cleanup_srcu; + goto out_cleanup_hwq_srcu; for (i = 0; i < set->nr_maps; i++) { set->map[i].mq_map = kcalloc_node(nr_cpu_ids, @@ -4819,6 +4823,8 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set) } kfree(set->tags); set->tags = NULL; +out_cleanup_hwq_srcu: + cleanup_srcu_struct(&set->update_nr_hwq_srcu); out_cleanup_srcu: if (set->flags & BLK_MQ_F_BLOCKING) cleanup_srcu_struct(set->srcu); @@ -5081,7 +5087,18 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues) { mutex_lock(&set->tag_list_lock); + /* + * Mark us in updating nr_hw_queues for preventing switching + * elevator + * + * Elevator switch code can _not_ acquire ->tag_list_lock + */ + set->flags |= BLK_MQ_F_UPDATE_HW_QUEUES; + synchronize_srcu(&set->update_nr_hwq_srcu); + __blk_mq_update_nr_hw_queues(set, nr_hw_queues); + + set->flags &= BLK_MQ_F_UPDATE_HW_QUEUES; mutex_unlock(&set->tag_list_lock); } EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues); diff --git a/block/elevator.c b/block/elevator.c index cf48613c6e62..7d7b77dd4341 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -718,9 +718,10 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, { char elevator_name[ELV_NAME_MAX]; char *name; - int ret; + int ret, idx; unsigned int memflags; struct request_queue *q = disk->queue; + struct blk_mq_tag_set *set = q->tag_set; /* * If the attribute needs to load a module, do it before freezing the @@ -732,6 +733,13 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, elv_iosched_load_module(name); + idx = srcu_read_lock(&set->update_nr_hwq_srcu); + + if (set->flags & BLK_MQ_F_UPDATE_HW_QUEUES) { + ret = -EBUSY; + goto exit; + } + memflags = blk_mq_freeze_queue(q); mutex_lock(&q->elevator_lock); ret = elevator_change(q, name); @@ -739,6 +747,8 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, ret = count; mutex_unlock(&q->elevator_lock); blk_mq_unfreeze_queue(q, memflags); +exit: + srcu_read_unlock(&set->update_nr_hwq_srcu, idx); return ret; } diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 8eb9b3310167..473871c760e1 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -527,6 +527,7 @@ struct blk_mq_tag_set { struct mutex tag_list_lock; struct list_head tag_list; struct srcu_struct *srcu; + struct srcu_struct update_nr_hwq_srcu; }; /** @@ -681,7 +682,14 @@ enum { */ BLK_MQ_F_NO_SCHED_BY_DEFAULT = 1 << 6, - BLK_MQ_F_MAX = 1 << 7, + /* + * True when updating nr_hw_queues is in-progress + * + * tag_set only flag, not usable for hctx + */ + BLK_MQ_F_UPDATE_HW_QUEUES = 1 << 7, + + BLK_MQ_F_MAX = 1 << 8, }; #define BLK_MQ_MAX_DEPTH (10240) -- 2.47.0
