Re: Racy loop device reuse logic
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: 2022-01-19 11:31:06
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@I-love.SAKURA.ne.jp . 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.