Re: [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union

[Marco Elver]

On Sat, 1 May 2021 at 02:37, Marco Elver <elver@xxxxxxxxxx> wrote:
> On Sat, 1 May 2021 at 01:48, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> >
> > Well with 7 patches instead of 3 that was a little more than I thought
> > I was going to send.
> >
> > However that does demonstrate what I am thinking, and I think most of
> > the changes are reasonable at this point.
> >
> > I am very curious how synchronous this all is, because if this code
> > is truly synchronous updating signalfd to handle this class of signal
> > doesn't really make sense.

Just a note on this: the reason for adding signalfd support was based
on the comment at SIL_FAULT_PKUERR:

>                 /*
>                   * Fall through to the SIL_FAULT case.  Both SIL_FAULT_BNDERR
>                   * and SIL_FAULT_PKUERR are only generated by faults that
>                   * deliver them synchronously to userspace.  In case someone
>                   * injects one of these signals and signalfd catches it treat
>                   * it as SIL_FAULT.
>                   */

The same would hold for SIL_FAULT_PERF_EVENT, where somebody injects
(re-injects perhaps?) such an event. But otherwise, yes,
non-synchronous handling of SIGTRAP/TRAP_PERF is pretty useless for
almost all usecases I can think of.

Thanks,
-- Marco