On Wed, 2008-04-09 at 15:39 +0400, Oleg Nesterov wrote: > On 04/09, David Woodhouse wrote: > > > > On Tue, 2008-04-08 at 15:35 +0400, Oleg Nesterov wrote: > > > Why do we need any flag? It looks a bit ugly. Isn't it better to introduce > > > the new magic ERESTART_XXX which means ERESTARTNOHAND + restore-sigmask ? > > > > > > We only need this flag as an implicit parameter to the arch dependent do_signal() > > > which we can't call directly, and thus it must imply TIF_SIGPENDING, and it > > > is not valid after do_signal() (should be cleared). This all looks like > > > ERESTART_ magic, why should we add something else ? > > > > > > See also http://marc.info/?l=linux-kernel&m=113734458516136 > > > > > > Of course, probably it is too late to change the implementation even if > > > I am right, the question is: what I am missed? > > > > Q: When ppoll() is interrupted by a signal, what signal mask should be > > active when the signal handler is active? > > > > I believe that the signal handler should run with the temporary sigmask > > which was set by ppoll(), and the original sigmask should be restored > > only when the handler completes -- and that's what we achieve with > > TIF_RESTORE_SIGMASK. > > Yes sure. > > > So a signal which was originally enabled but is temporarily disabled by > > the mask passed to ppoll() will not be able to interrupt the handler for > > the signal which interrupted ppoll(). > > > > Your version will restore the original signal mask _before_ invoking the > > signal handler which interrupted ppoll() > > Why do you think so? > > Please look at the "patch" below, > > --- arch/x86/kernel/signal_32.c 2008-02-15 16:58:38.000000000 +0300 > +++ - 2008-04-09 15:16:05.393510662 +0400 > @@ -526,10 +526,14 @@ handle_signal(unsigned long sig, siginfo > { > int ret; > > + oldset = ¤t->blocked; > + > /* Are we from a system call? */ > if (regs->orig_ax >= 0) { > /* If so, check system call restarting.. */ > switch (regs->ax) { > + case -ERESTART_XXX: > + oldset = ¤t->saved_sigmask; > case -ERESTART_RESTARTBLOCK: > case -ERESTARTNOHAND: > regs->ax = -EINTR; > > We also need a similar change in do_signal(). Now, > > --- fs/select.c 2008-02-15 16:59:15.000000000 +0300 > +++ - 2008-04-09 15:19:29.015991911 +0400 > @@ -805,9 +805,8 @@ asmlinkage long sys_ppoll(struct pollfd > if (sigmask) { > memcpy(¤t->saved_sigmask, &sigsaved, > sizeof(sigsaved)); > - set_thread_flag(TIF_RESTORE_SIGMASK); > } > - ret = -ERESTARTNOHAND; > + ret = -ERESTART_XXX; > } else if (sigmask) > sigprocmask(SIG_SETMASK, &sigsaved, NULL); > > Perhaps I missed something else, though. Not that I really think it worth > changing, but I'll try to make a proof of concept patch on Weekend, on top > of Roland's cleanups. > > As I see it, the main disadvantage of ERESTART_ approach is that we need 2 > new ERESTART_ codes, one for ERESTARTNOHAND, another for ERESTART_RESTARTBLOCK. > And yes, while I personally think this is "more clean", it is very subjective. One error code more or less, that's cheap. Thread flags are a much more limited resource. Just my two cents, Petr Tesarik -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
