Re: [PATCH v2] binder: Don't use mmput() from shrinker function.

[Christian Brauner]

On Thu, Jul 16, 2020 at 05:17:56PM +0200, Michal Hocko wrote:
> On Fri 17-07-20 00:12:15, Tetsuo Handa wrote:
> > syzbot is reporting that mmput() from shrinker function has a risk of
> > deadlock [1], for delayed_uprobe_add() from update_ref_ctr() calls
> > kzalloc(GFP_KERNEL) with delayed_uprobe_lock held, and
> > uprobe_clear_state() from __mmput() also holds delayed_uprobe_lock.
> > 
> > Commit a1b2289cef92ef0e ("android: binder: drop lru lock in isolate
> > callback") replaced mmput() with mmput_async() in order to avoid sleeping
> > with spinlock held. But this patch replaces mmput() with mmput_async() in
> > order not to start __mmput() from shrinker context.
> > 
> > [1] https://syzkaller.appspot.com/bug?id=bc9e7303f537c41b2b0cc2dfcea3fc42964c2d45
> > 
> > Reported-by: syzbot <syzbot+1068f09c44d151250c33@xxxxxxxxxxxxxxxxxxxxxxxxx>
> > Reported-by: syzbot <syzbot+e5344baa319c9a96edec@xxxxxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> 
> Reviewed-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks for the careful review Michal!
Does this need a Cc: stable?

Otherwise

Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>

Thanks!
Christian