[dm-devel] block: flush queued bios when the process blocks

[Mikulas Patocka]

On Mon, 5 Oct 2015, Mike Snitzer wrote:

> FYI, I've put rebased versions of your 2 patches in my wip branch, see:
> http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/log/?h=wip

I found a bug in the first patch 
(http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=wip&id=2e90df2e9cf482f45be4230152535fdab525fbd8)

There is this piece of code:

	spin_lock(&bs->rescue_lock);
	bio_list_add(&bs->rescue_list, bio);
	spin_unlock(&bs->rescue_lock);
	queue_work(bs->rescue_workqueue, &bs->rescue_work);

It is possible that after spin_unlock and before queue_work the bio is 
finished by previous workqueue invocation. When the bio is finished, it is 
possible that the block device is unloaded and queue_work accesses freed 
memory.

Change the code so that queue_work is executed inside the spinlock:
	spin_lock(&bs->rescue_lock);
	bio_list_add(&bs->rescue_list, bio);
	queue_work(bs->rescue_workqueue, &bs->rescue_work);
	spin_unlock(&bs->rescue_lock);

Mikulas