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SubjectRe: [RFC] TIF_NOTIFY_RESUME, arch/*/*/*signal*.c and all such
On 04/25, Al Viro wrote:
>
> On Wed, Apr 25, 2012 at 05:46:11PM +0200, Oleg Nesterov wrote:
> >
> > --- x/arch/x86/kernel/signal.c
> > +++ x/arch/x86/kernel/signal.c
> > @@ -711,6 +711,13 @@ handle_signal(unsigned long sig, siginfo
> > regs->ax = regs->orig_ax;
> > regs->ip -= 2;
> > break;
> > +
> > + case -EINTR:
> > + break;
> > +
> > + default:
> > + if (regs->orig_ax == NR_eintr)
> > + regs->ax = NR_eintr;
> > }
> > }
> >
> > @@ -791,6 +798,7 @@ static void do_signal(struct pt_regs *re
> > case -ERESTARTSYS:
> > case -ERESTARTNOINTR:
> > regs->ax = regs->orig_ax;
> > + regs->orig_ax = NR_eintr;
> > regs->ip -= 2;
> > break;
> >
> >
> > this ignores ERESTART_RESTARTBLOCK for simplicity.
>
> Ehh... You do realize that it's that simple only on architectures that
> have syscall number in a register?

No, I do not ;) I simply know nothing about other architectures.

> Take a look at e.g. insert_restart_trampoline()
> in arch/parisc/kernel/signal.c

Will do. Not sure I will be able to undestand it though. And btw I still
didn't look at the signal patches in your tree, I've just returned from
vacation today.

> I'm not sure that SA_RESTART case is actually worth bothering with -

Neither me. But,

> AFAICS, your mechanism won't cover SA_RESTART/SA_RESTART/!SA_RESTART
> combinations anyway,

Confused. The hack above doesn't even try to cover this case (and it is
obviously wrong in ERESTARTSYS/NOINTR case), I only tried to illustrate
the idea.

> syscall interrupted
> SA_RESTART signal arrives, handler1 entered
> !SA_RESTART signal arrives, handler2 entered
> handler2 returns
> hander1 returns
> syscall restarts

And there is another case:

syscall interrupted, it returns ERESTARTSYS.

do_signal() sees no signal, restarts the syscall

!SA_RESTART comes before we return to user-mode

This doesn't really differ from sigsuspend/ERESTARTNOHAND we discussed
before.

Oleg.



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