A queue's elevator can be updated either when modifying nr_hw_queues or through the sysfs scheduler attribute. To prevent simultaneous updates from causing race conditions, introduce a dedicated lock q->elevator_lock. Currently, elevator switching/updating is protected using q->sysfs_lock, but this has led to lockdep splats[1] due to inconsistent lock ordering between q->sysfs_lock and the freeze-lock in multiple block layer call sites. As the scope of q->sysfs_lock is not well-defined, its misuse has resulted in numerous lockdep warnings. To resolve this, replace q-> sysfs_lock with a new dedicated q->elevator_lock, which will be exclusively used to protect elevator switching and updates. [1] https://lore.kernel.org/all/67637e70.050a0220.3157ee.000c.GAE@xxxxxxxxxx/ Signed-off-by: Nilay Shroff <nilay@xxxxxxxxxxxxx> --- block/blk-core.c | 1 + block/blk-mq.c | 12 ++-- block/blk-sysfs.c | 133 ++++++++++++++++++++++++++++------------- block/elevator.c | 18 ++++-- block/genhd.c | 9 ++- include/linux/blkdev.h | 1 + 6 files changed, 119 insertions(+), 55 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index d6c4fa3943b5..222cdcb662c2 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -431,6 +431,7 @@ struct request_queue *blk_alloc_queue(struct queue_limits *lim, int node_id) mutex_init(&q->debugfs_mutex); mutex_init(&q->sysfs_lock); mutex_init(&q->limits_lock); + mutex_init(&q->elevator_lock); mutex_init(&q->rq_qos_mutex); spin_lock_init(&q->queue_lock); diff --git a/block/blk-mq.c b/block/blk-mq.c index 40490ac88045..f58e11dee8a0 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -4467,7 +4467,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, unsigned long i, j; /* protect against switching io scheduler */ - mutex_lock(&q->sysfs_lock); + mutex_lock(&q->elevator_lock); for (i = 0; i < set->nr_hw_queues; i++) { int old_node; int node = blk_mq_get_hctx_node(set, i); @@ -4500,7 +4500,7 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, xa_for_each_start(&q->hctx_table, j, hctx, j) blk_mq_exit_hctx(q, set, hctx, j); - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->elevator_lock); /* unregister cpuhp callbacks for exited hctxs */ blk_mq_remove_hw_queues_cpuhp(q); @@ -4934,7 +4934,7 @@ static bool blk_mq_elv_switch_none(struct list_head *head, return false; /* q->elevator needs protection from ->sysfs_lock */ - mutex_lock(&q->sysfs_lock); + mutex_lock(&q->elevator_lock); /* the check has to be done with holding sysfs_lock */ if (!q->elevator) { @@ -4950,7 +4950,7 @@ static bool blk_mq_elv_switch_none(struct list_head *head, list_add(&qe->node, head); elevator_disable(q); unlock: - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->elevator_lock); return true; } @@ -4980,11 +4980,11 @@ static void blk_mq_elv_switch_back(struct list_head *head, list_del(&qe->node); kfree(qe); - mutex_lock(&q->sysfs_lock); + mutex_lock(&q->elevator_lock); elevator_switch(q, t); /* drop the reference acquired in blk_mq_elv_switch_none */ elevator_put(t); - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->elevator_lock); } static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 7e22ec96f2b3..355dfb514712 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -58,7 +58,13 @@ queue_var_store(unsigned long *var, const char *page, size_t count) static ssize_t queue_requests_show(struct gendisk *disk, char *page) { - return queue_var_show(disk->queue->nr_requests, page); + int ret; + + mutex_lock(&disk->queue->sysfs_lock); + ret = queue_var_show(disk->queue->nr_requests, page); + mutex_unlock(&disk->queue->sysfs_lock); + + return ret; } static ssize_t @@ -66,27 +72,42 @@ queue_requests_store(struct gendisk *disk, const char *page, size_t count) { unsigned long nr; int ret, err; + unsigned int memflags; + struct request_queue *q = disk->queue; - if (!queue_is_mq(disk->queue)) - return -EINVAL; + mutex_lock(&q->sysfs_lock); + memflags = blk_mq_freeze_queue(q); + + if (!queue_is_mq(disk->queue)) { + ret = -EINVAL; + goto out; + } ret = queue_var_store(&nr, page, count); if (ret < 0) - return ret; + goto out; if (nr < BLKDEV_MIN_RQ) nr = BLKDEV_MIN_RQ; err = blk_mq_update_nr_requests(disk->queue, nr); if (err) - return err; - + ret = err; +out: + blk_mq_unfreeze_queue(q, memflags); + mutex_unlock(&q->sysfs_lock); return ret; } static ssize_t queue_ra_show(struct gendisk *disk, char *page) { - return queue_var_show(disk->bdi->ra_pages << (PAGE_SHIFT - 10), page); + int ret; + + mutex_lock(&disk->queue->sysfs_lock); + ret = queue_var_show(disk->bdi->ra_pages << (PAGE_SHIFT - 10), page); + mutex_unlock(&disk->queue->sysfs_lock); + + return ret; } static ssize_t @@ -94,11 +115,19 @@ queue_ra_store(struct gendisk *disk, const char *page, size_t count) { unsigned long ra_kb; ssize_t ret; + unsigned int memflags; + struct request_queue *q = disk->queue; + + mutex_lock(&q->sysfs_lock); + memflags = blk_mq_freeze_queue(q); ret = queue_var_store(&ra_kb, page, count); if (ret < 0) - return ret; + goto out; disk->bdi->ra_pages = ra_kb >> (PAGE_SHIFT - 10); +out: + blk_mq_unfreeze_queue(q, memflags); + mutex_unlock(&q->sysfs_lock); return ret; } @@ -534,14 +563,24 @@ static ssize_t queue_var_store64(s64 *var, const char *page) static ssize_t queue_wb_lat_show(struct gendisk *disk, char *page) { - if (!wbt_rq_qos(disk->queue)) - return -EINVAL; + int ret; + + mutex_lock(&disk->queue->sysfs_lock); + + if (!wbt_rq_qos(disk->queue)) { + ret = -EINVAL; + goto out; + } if (wbt_disabled(disk->queue)) - return sysfs_emit(page, "0\n"); + ret = sysfs_emit(page, "0\n"); + else + ret = sysfs_emit(page, "%llu\n", + div_u64(wbt_get_min_lat(disk->queue), 1000)); - return sysfs_emit(page, "%llu\n", - div_u64(wbt_get_min_lat(disk->queue), 1000)); +out: + mutex_unlock(&disk->queue->sysfs_lock); + return ret; } static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page, @@ -551,18 +590,24 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page, struct rq_qos *rqos; ssize_t ret; s64 val; + unsigned int memflags; + + mutex_lock(&q->sysfs_lock); + memflags = blk_mq_freeze_queue(q); ret = queue_var_store64(&val, page); if (ret < 0) - return ret; - if (val < -1) - return -EINVAL; + goto out; + if (val < -1) { + ret = -EINVAL; + goto out; + } rqos = wbt_rq_qos(q); if (!rqos) { ret = wbt_init(disk); if (ret) - return ret; + goto out; } if (val == -1) @@ -570,8 +615,10 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page, else if (val >= 0) val *= 1000ULL; - if (wbt_get_min_lat(q) == val) - return count; + if (wbt_get_min_lat(q) == val) { + ret = count; + goto out; + } /* * Ensure that the queue is idled, in case the latency update @@ -584,7 +631,10 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page, blk_mq_unquiesce_queue(q); - return count; +out: + blk_mq_unfreeze_queue(q, memflags); + mutex_unlock(&q->sysfs_lock); + return ret; } QUEUE_RW_ENTRY(queue_wb_lat, "wbt_lat_usec"); @@ -593,7 +643,7 @@ QUEUE_RW_ENTRY(queue_wb_lat, "wbt_lat_usec"); /* Common attributes for bio-based and request-based queues. */ static struct attribute *queue_attrs[] = { /* - * attributes protected with q->sysfs_lock + * attributes which require some form of locking */ &queue_ra_entry.attr, @@ -652,10 +702,10 @@ static struct attribute *queue_attrs[] = { /* Request-based queue attributes that are not relevant for bio-based queues. */ static struct attribute *blk_mq_queue_attrs[] = { /* - * attributes protected with q->sysfs_lock + * attributes which require some form of locking */ - &queue_requests_entry.attr, &elv_iosched_entry.attr, + &queue_requests_entry.attr, #ifdef CONFIG_BLK_WBT &queue_wb_lat_entry.attr, #endif @@ -729,10 +779,7 @@ queue_attr_show(struct kobject *kobj, struct attribute *attr, char *page) return res; } - mutex_lock(&disk->queue->sysfs_lock); - res = entry->show(disk, page); - mutex_unlock(&disk->queue->sysfs_lock); - return res; + return entry->show(disk, page); } static ssize_t @@ -778,12 +825,7 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr, return length; } - mutex_lock(&q->sysfs_lock); - memflags = blk_mq_freeze_queue(q); - res = entry->store(disk, page, length); - blk_mq_unfreeze_queue(q, memflags); - mutex_unlock(&q->sysfs_lock); - return res; + return entry->store(disk, page, length); } static const struct sysfs_ops queue_sysfs_ops = { @@ -852,15 +894,19 @@ int blk_register_queue(struct gendisk *disk) if (ret) goto out_debugfs_remove; + ret = blk_crypto_sysfs_register(disk); + if (ret) + goto out_unregister_ia_ranges; + + mutex_lock(&q->elevator_lock); if (q->elevator) { ret = elv_register_queue(q, false); - if (ret) - goto out_unregister_ia_ranges; + if (ret) { + mutex_unlock(&q->elevator_lock); + goto out_crypto_sysfs_unregister; + } } - - ret = blk_crypto_sysfs_register(disk); - if (ret) - goto out_elv_unregister; + mutex_unlock(&q->elevator_lock); blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q); wbt_enable_default(disk); @@ -885,8 +931,8 @@ int blk_register_queue(struct gendisk *disk) return ret; -out_elv_unregister: - elv_unregister_queue(q); +out_crypto_sysfs_unregister: + blk_crypto_sysfs_unregister(disk); out_unregister_ia_ranges: disk_unregister_independent_access_ranges(disk); out_debugfs_remove: @@ -932,8 +978,11 @@ void blk_unregister_queue(struct gendisk *disk) blk_mq_sysfs_unregister(disk); blk_crypto_sysfs_unregister(disk); - mutex_lock(&q->sysfs_lock); + mutex_lock(&q->elevator_lock); elv_unregister_queue(q); + mutex_unlock(&q->elevator_lock); + + mutex_lock(&q->sysfs_lock); disk_unregister_independent_access_ranges(disk); mutex_unlock(&q->sysfs_lock); diff --git a/block/elevator.c b/block/elevator.c index cd2ce4921601..6ee372f0220c 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -457,7 +457,7 @@ int elv_register_queue(struct request_queue *q, bool uevent) struct elevator_queue *e = q->elevator; int error; - lockdep_assert_held(&q->sysfs_lock); + lockdep_assert_held(&q->elevator_lock); error = kobject_add(&e->kobj, &q->disk->queue_kobj, "iosched"); if (!error) { @@ -481,7 +481,7 @@ void elv_unregister_queue(struct request_queue *q) { struct elevator_queue *e = q->elevator; - lockdep_assert_held(&q->sysfs_lock); + lockdep_assert_held(&q->elevator_lock); if (e && test_and_clear_bit(ELEVATOR_FLAG_REGISTERED, &e->flags)) { kobject_uevent(&e->kobj, KOBJ_REMOVE); @@ -618,7 +618,7 @@ int elevator_switch(struct request_queue *q, struct elevator_type *new_e) unsigned int memflags; int ret; - lockdep_assert_held(&q->sysfs_lock); + lockdep_assert_held(&q->elevator_lock); memflags = blk_mq_freeze_queue(q); blk_mq_quiesce_queue(q); @@ -655,7 +655,7 @@ void elevator_disable(struct request_queue *q) { unsigned int memflags; - lockdep_assert_held(&q->sysfs_lock); + lockdep_assert_held(&q->elevator_lock); memflags = blk_mq_freeze_queue(q); blk_mq_quiesce_queue(q); @@ -723,11 +723,19 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, { char elevator_name[ELV_NAME_MAX]; int ret; + unsigned int memflags; + struct request_queue *q = disk->queue; strscpy(elevator_name, buf, sizeof(elevator_name)); + + memflags = blk_mq_freeze_queue(q); + mutex_lock(&q->elevator_lock); ret = elevator_change(disk->queue, strstrip(elevator_name)); + mutex_unlock(&q->elevator_lock); + blk_mq_unfreeze_queue(q, memflags); if (!ret) return count; + return ret; } @@ -738,6 +746,7 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name) struct elevator_type *cur = NULL, *e; int len = 0; + mutex_lock(&q->elevator_lock); if (!q->elevator) { len += sprintf(name+len, "[none] "); } else { @@ -755,6 +764,7 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name) spin_unlock(&elv_list_lock); len += sprintf(name+len, "\n"); + mutex_unlock(&q->elevator_lock); return len; } diff --git a/block/genhd.c b/block/genhd.c index e9375e20d866..c2bd86cd09de 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -565,8 +565,11 @@ int __must_check add_disk_fwnode(struct device *parent, struct gendisk *disk, if (disk->major == BLOCK_EXT_MAJOR) blk_free_ext_minor(disk->first_minor); out_exit_elevator: - if (disk->queue->elevator) + if (disk->queue->elevator) { + mutex_lock(&disk->queue->elevator_lock); elevator_exit(disk->queue); + mutex_unlock(&disk->queue->elevator_lock); + } return ret; } EXPORT_SYMBOL_GPL(add_disk_fwnode); @@ -742,9 +745,9 @@ void del_gendisk(struct gendisk *disk) blk_mq_quiesce_queue(q); if (q->elevator) { - mutex_lock(&q->sysfs_lock); + mutex_lock(&q->elevator_lock); elevator_exit(q); - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->elevator_lock); } rq_qos_exit(q); blk_mq_unquiesce_queue(q); diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 248416ecd01c..5690d2f3588e 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -562,6 +562,7 @@ struct request_queue { struct mutex sysfs_lock; struct mutex limits_lock; + struct mutex elevator_lock; /* * for reusing dead hctx instance in case of updating -- 2.47.1
