On 25 June 2013 22:40, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 24 Jun 2013 10:10:08 +0100 James Hogan <james.hogan@xxxxxxxxxx> wrote: > >> On 22/06/13 20:09, Oleg Nesterov wrote: >> > On 06/21, David Daney wrote: >> >> I am proposing that we just reduce the number of usable signals such >> >> that existing libc status checking macros/functions don't change in any >> >> way. >> > >> > And I fully agree! Absolutely, sorry for confusion. >> > >> > >> > What I tried to say, _if_ we change the ABI instead, lets make this >> > change sane. >> >> I agree that this approach isn't very nice (I was really just trying to >> explore the options) and reducing the number of signals is nicer. But is >> anybody here confident enough that the number of signals changing under >> the feet of existing binaries/libc won't actually break anything real? >> I.e. anything trying to use SIGRTMAX() to get a lower priority signal. > > Meanwhile, unprivileged users can make a MIPS kernel go BUG. > > How much of a problem is this? Obviously less of a problem with MIPS > than it would be with some other CPU types, but I'd imagine it's still > awkward in some environments. > > If this _is_ considered a problem, can we think of some nasty little > hack which at least makes the effects less damaging, which we can also > put into -stable kernels? The first rfc patch I sent sort of satisfies that by passing 127 if sig==128, or slightly better would be passing 126 if sig>=127 (so that SIFSIGNALED returns true). Effectively #ifdef'ing it on _NSIG>127 as this patch does may be preferable too. That's probably the minimum change necessary to evade the BUG_ON without removing it. The wait status code will still be wrong, but it wasn't exactly right before so it's no worse. IMO changing the ABI by reducing _NSIG to 127 or 126 isn't appropriate for stable. Cheers James
