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.
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-mq-debugfs.c | 1 +
block/elevator.c | 5 ++++-
block/genhd.c | 12 ++++++++++++
include/linux/blkdev.h | 3 +++
4 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 2837a8ce8054..29b3540dd180 100644
--- 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 fd0bcf22aaee..98a754f58de5 100644
--- 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;
@@ -730,7 +733,7 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
struct blk_mq_tag_set *set = q->tag_set;
/* Make sure queue is not in the middle of being removed */
- if (!blk_queue_registered(q))
+ if (!blk_queue_registered(q) || blk_queue_no_elv_switch(q))
return -ENOENT;
/*
diff --git a/block/genhd.c b/block/genhd.c
index 0c34cc1a4eae..0e64e7400fb4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -749,6 +749,15 @@ static void __del_gendisk(struct gendisk *disk)
blk_unfreeze_release_lock(q);
}
+static void disable_elv_switch(struct request_queue *q)
+{
+ WARN_ON_ONCE(!queue_is_mq(q));
+
+ mutex_lock(&q->elevator_lock);
+ blk_queue_flag_set(QUEUE_FLAG_NO_ELV_SWITCH, q);
+ mutex_unlock(&q->elevator_lock);
+}
+
/**
* del_gendisk - remove the gendisk
* @disk: the struct gendisk to remove
@@ -777,6 +786,9 @@ 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 9c373cf0eb47..b15c53fabe9f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -645,6 +645,7 @@ 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
};
@@ -682,6 +683,8 @@ 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);
--
2.47.0
