Hi,
在 2025/08/03 21:41, Ujwal Kundur 写道:
A potential unsafe locking scenario presents itself when
mutex_lock(&disk->open_mutex) is called with reader's lock held on
update_nr_hwq_lock:
CPU0 CPU1
---- ----
rlock(&set->update_nr_hwq_lock)
lock(&nbd->config_lock);
lock(&set->update_nr_hwq_lock);
lock(&disk->open_mutex)
This problem is already fixed inside nbd by:
8b428f42f3ed ("nbd: fix lockdep deadlock warning")
Thanks,
Kuai
When the gendisk is added back concurrently, a writer's lock is
attempted to be held on update_nr_hwq_lock while holding other locks in
the call-path, becoming a potential source of deadlock(s).
Scope read-critical section to blk_unregister_queue, which is the only
function that interacts with switching elevator and requires
synchronization with update_nr_hwq_lock.
Reported-by: syzbot+2e9e529ac0b319316453@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ujwal Kundur <ujwal.kundur@xxxxxxxxx>
---
block/genhd.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
mode change 100644 => 100755 block/genhd.c
diff --git a/block/genhd.c b/block/genhd.c
old mode 100644
new mode 100755
index c26733f6324b..b56f09f5699b
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -696,6 +696,7 @@ static void __del_gendisk(struct gendisk *disk)
struct block_device *part;
unsigned long idx;
bool start_drain;
+ struct blk_mq_tag_set *set = q->tag_set;
might_sleep();
@@ -740,7 +741,9 @@ static void __del_gendisk(struct gendisk *disk)
bdi_unregister(disk->bdi);
}
+ down_read(&set->update_nr_hwq_lock);
blk_unregister_queue(disk);
+ up_read(&set->update_nr_hwq_lock);
kobject_put(disk->part0->bd_holder_dir);
kobject_put(disk->slave_dir);
@@ -808,20 +811,15 @@ static void disable_elv_switch(struct request_queue *q)
*/
void del_gendisk(struct gendisk *disk)
{
- struct blk_mq_tag_set *set;
unsigned int memflags;
if (!queue_is_mq(disk->queue)) {
__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);
- up_read(&set->update_nr_hwq_lock);
memalloc_noio_restore(memflags);
}
}
