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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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