Re: [PATCH v6] loop: Fix NULL pointer dereference in lo_rw_aio()

[Bart Van Assche]

On 8/24/26 3:06 PM, Tetsuo Handa wrote:
> but sashiko found problems with Bart's series ( https://sashiko.dev/
> #/patchset/8330ca0e-b4d9-451a-bc0d-a50178194ea8@xxxxxxxxxxxxxxxxxxx
> and https://sashiko.dev/#/patchset/2efb1032-34b9-4c31-
> b6fc-4aa9b1d60895@xxxxxxxxxxxxxxxxxxx ).

Thanks, I had not yet seen this feedback from Sashiko. My conclusion is
that two of the three Sashiko findings are wrong. I will fix the third
one - the finding about the potential wait-die deadlock.

> I still cannot catch why Bart's approach can become safe without
> synchronize_rcu() and drain_workqueue().

Agreed that drain_workqueue() or flush_workqueue() is necessary. I do
not agree that an explicit synchronize_rcu() call is required. Waiting
until the request queue is frozen includes this call implicitly.
See also __percpu_ref_switch_to_atomic().

Thanks,

Bart.