Re: dm: free io_barrier after blk_cleanup_queue call

From: Tahsin Erdogan
Date: Mon Oct 10 2016 - 10:52:11 EST

On Mon, Oct 10, 2016 at 6:25 AM, Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> I have to believe this was born out of code inspection rather than
> actual need (due to crash, etc)?

This got originated from several crashes I have seen with 4.3 kernel.
The crashes
were caused by null dereferencing of io_barrier->per_cpu_ref.

The issue may no longer be relevant after commit c91852ff0815
("dm: optimize dm_request_fn()") because conditions for accessing
io_barrier may not longer exist. But fix should be considered for
forked stable trees.