Re: Racy loop device reuse logic

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I found a way to avoid this race by splitting lo_open() into two phases using task_work_add().
Christoph Hellwig is trying to take a look at https://lkml.kernel.org/r/f6b947d0-1047-66b3-0243-af5017c9ab55@xxxxxxxxxxxxxxxxxxx .

On 2022/01/12 22:16, Jan Kara wrote:
> I don't think we can fully solve this race in the kernel and IMO it is
> futile to try that - depending on when exactly systemd-udev decides to

s/systemd-udev/systemd-udevd/g

> close /dev/loop0 and how exactly mount decides to implement its loop device
> reuse, different strategies will / will not work.

Assuming memory leak

 +	spin_unlock(&loop_delete_spinlock);
-+	if (err)
-+		return err;
++	if (err) {
++		kfree(lot);
++		kfree(lrt);
++		return err;
++	}
 +	/* Add to spool, for -ENOMEM upon release() cannot be handled. */

in that patch is fixed, trying to solve this race on the kernel side looks not such bad.




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