On Mon, Dec 07, 2020 at 11:17:29AM +0530, Naresh Kamboju wrote:
While running "mkfs -t ext4" on arm64 juno-r2 device connected with SSD drive the following kernel warning reported on stable rc 5.9.13-rc1 kernel.
Steps to reproduce:
# boot arm64 Juno-r2 device with stable-rc 5.9.13-rc1. # Connect SSD drive # Format the file system ext4 type mkfs -t ext4 <SSD-drive> # you will notice this warning
Does it happen easily? Can you bisect?
Crash log:
Writing superblocks and filesystem accounting information: 0/895 [ 86.131095] [ 86.132592] ===================================== [ 86.137300] WARNING: bad unlock balance detected! [ 86.142012] 5.9.13-rc1 #1 Not tainted [ 86.145675] ------------------------------------- [ 86.150384] mkfs.ext4/426 is trying to release lock (rcu_read_lock) at: [ 86.157020] [<ffff80001063478c>] blk_queue_exit+0xcc/0x1b0 [ 86.162511] but there are no more locks to release!
This really doesn't make much sense. blk_queue_exit() in 5.9.12 does:
percpu_ref_put(&q->q_usage_counter); (literally, that's the entire function)
percpu_ref_put() does:
rcu_read_lock();
if (__ref_is_percpu(ref, &percpu_count)) this_cpu_sub(*percpu_count, nr); else if (unlikely(atomic_long_sub_and_test(nr, &ref->count))) ref->release(ref);
rcu_read_unlock();
Unless ->release() has an unbalanced rcu_read_unlock(), there definitely is a lock to release! Some archaeology says that ->release is blk_queue_usage_counter_release(), which calls wake_up_all(&q->mq_freeze_wq);
which doesn't appear to use RCU at all. So this trace makes no sense, and all I can do is ask you to bisect it.