Re: [PATCH 1/3] usb: ucsi: Add missing ppm_lock

[Christian A. Ehrhardt]

On Wed, Jan 17, 2024 at 06:44:40AM +0100, Greg Kroah-Hartman wrote:
> On Tue, Jan 16, 2024 at 11:40:39PM +0100, Christian A. Ehrhardt wrote:
> > Calling ->sync_write must be done while holding the PPM lock as the
> > mailbox logic does not support concurrent commands.
> > 
> > Thus protect the only call to ucsi_acknowledge_connector_change
> > with the PPM lock as it calls ->sync_write. All other calls to
> > ->sync_write already happen under the PPM lock.
> > 
> > Signed-off-by: Christian A. Ehrhardt <lk@xxxxxxx>
> > ---
> > NOTE: This is not a theoretical issue. I've seen problems resulting
> > from the missing lock on real hardware.
> 
> What commit id does this fix?

It's hard to tell (due to rewrites, logic and API changes). After
digging a bit more I think it is at least a theoretical issues since
the introduction of partner tasks.

I'll wait a bit for additional feedback and fix this and other issues
noticed by your patch bot (sorry for those) in the next iteration.

> Should it be cc: stable?

Not sure. The race is triggered much more ofter after the quirk added
in patch 3/3, so this may not be a practical issue before that.
I'll add the tag in the next iteration, though.

   thanks   Christian