Re: WARNING in timer_wait_running

[Frederic Weisbecker]

On Fri, Apr 07, 2023 at 07:47:40PM +0200, Thomas Gleixner wrote:
> On Fri, Apr 07 2023 at 13:50, Frederic Weisbecker wrote:
> > On Fri, Apr 07, 2023 at 10:44:22AM +0200, Thomas Gleixner wrote:
> >> Now memory came back. The problem with posix CPU timers is that it is
> >> not really known to the other side which task is actually doing the
> >> expiry. For process wide timers this could be any task in the process.
> >> 
> >> For hrtimers this works because the expiring context is known.
> >
> > So if posix_cpu_timer_del() were to clear ctmr->pid to NULL and then
> > delay put_pid() with RCU, we could retrieve that information without
> > holding the timer lock (with appropriate RCU accesses all around).
> 
> No, you can't. This only gives you the process, but the expiry might run
> on any task of that. To make that work you need a mutex in sighand.

Duh right missed that. Ok will try.