block: add new helper for disabling elevator switch when deleting disk

Add new helper disable_elv_switch() and new flag QUEUE_FLAG_NO_ELV_SWITCH
for disabling elevator switch before deleting disk:

- originally flag QUEUE_FLAG_REGISTERED is added for preventing elevator
switch during removing disk, but this flag has been used widely for
other purposes, so add one new flag for disabling elevator switch only

- for avoiding deadlock risk, we have to move elevator queue
register/unregister out of elevator lock and queue freeze, which will be
done in next patch. However, this way adds small race window between elevator
switch and deleting ->queue_kobj, in which elevator queue register/unregister
could be run concurrently. The added helper will be used for avoiding the race
in the following patch.

- drain in-progress elevator switch before deleting disk

Suggested-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-21-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 2837a8ce8054236bf2bcff1ea67e5eed3f2d04a8..29b3540dd1804dd2afd40e1dd54e3d30fab9552c 100644 (file)
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -94,6 +94,7 @@ static const char *const blk_queue_flag_name[] = {
        QUEUE_FLAG_NAME(HCTX_ACTIVE),
        QUEUE_FLAG_NAME(SQ_SCHED),
        QUEUE_FLAG_NAME(DISABLE_WBT_DEF),
+       QUEUE_FLAG_NAME(NO_ELV_SWITCH),
 };
 #undef QUEUE_FLAG_NAME
 

diff --git a/block/elevator.c b/block/elevator.c
index 2edaf84900fcef78bf51294bf9db3a979bdc0fd4..f7e333abefe34daa39e2b11cab6d07998ffe7d95 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -680,6 +680,9 @@ void elevator_set_default(struct request_queue *q)
        };
        int err = 0;
 
+       /* now we allow to switch elevator */
+       blk_queue_flag_clear(QUEUE_FLAG_NO_ELV_SWITCH, q);
+
        if (q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
                return;
 
@@ -744,9 +747,13 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
        elv_iosched_load_module(ctx.name);
 
        down_read(&set->update_nr_hwq_lock);
-       ret = elevator_change(q, &ctx);
-       if (!ret)
-               ret = count;
+       if (!blk_queue_no_elv_switch(q)) {
+               ret = elevator_change(q, &ctx);
+               if (!ret)
+                       ret = count;
+       } else {
+               ret = -ENOENT;
+       }
        up_read(&set->update_nr_hwq_lock);
        return ret;
 }

diff --git a/block/genhd.c b/block/genhd.c
index f192fe4808b96744cacca5cc5526b859d351c3d3..a8cb5607b6e3d303288b5505a1d122a6010e16b8 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -764,6 +764,16 @@ static void __del_gendisk(struct gendisk *disk)
                blk_unfreeze_release_lock(q);
 }
 
+static void disable_elv_switch(struct request_queue *q)
+{
+       struct blk_mq_tag_set *set = q->tag_set;
+       WARN_ON_ONCE(!queue_is_mq(q));
+
+       down_write(&set->update_nr_hwq_lock);
+       blk_queue_flag_set(QUEUE_FLAG_NO_ELV_SWITCH, q);
+       up_write(&set->update_nr_hwq_lock);
+}
+
 /**
  * del_gendisk - remove the gendisk
  * @disk: the struct gendisk to remove
@@ -792,6 +802,9 @@ void del_gendisk(struct gendisk *disk)
                __del_gendisk(disk);
        } else {
                set = disk->queue->tag_set;
+
+               disable_elv_switch(disk->queue);
+
                memflags = memalloc_noio_save();
                down_read(&set->update_nr_hwq_lock);
                __del_gendisk(disk);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c36d7a1c2cc06e432f1b705b4790bec4bff87d7e..3aa1fd637d5774d80949a38a7eb38b0925434ea7 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -642,6 +642,7 @@ enum {
        QUEUE_FLAG_HCTX_ACTIVE,         /* at least one blk-mq hctx is active */
        QUEUE_FLAG_SQ_SCHED,            /* single queue style io dispatch */
        QUEUE_FLAG_DISABLE_WBT_DEF,     /* for sched to disable/enable wbt */
+       QUEUE_FLAG_NO_ELV_SWITCH,       /* can't switch elevator any more */
        QUEUE_FLAG_MAX
 };
 
@@ -679,6 +680,8 @@ void blk_queue_flag_clear(unsigned int flag, struct request_queue *q);
        ((q)->limits.features & BLK_FEAT_SKIP_TAGSET_QUIESCE)
 #define blk_queue_disable_wbt(q)       \
        test_bit(QUEUE_FLAG_DISABLE_WBT_DEF, &(q)->queue_flags)
+#define blk_queue_no_elv_switch(q)     \
+       test_bit(QUEUE_FLAG_NO_ELV_SWITCH, &(q)->queue_flags)
 
 extern void blk_set_pm_only(struct request_queue *q);
 extern void blk_clear_pm_only(struct request_queue *q);