linux-kernel - RE: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user

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Date:   Wed, 12 Jun 2019 13:24:38 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Eric W. Biederman'" <ebiederm@...ssion.com>
CC:     'Oleg Nesterov' <oleg@...hat.com>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        'Deepa Dinamani' <deepa.kernel@...il.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'arnd@...db.de'" <arnd@...db.de>,
        "'dbueso@...e.de'" <dbueso@...e.de>,
        "'axboe@...nel.dk'" <axboe@...nel.dk>,
        "'dave@...olabs.net'" <dave@...olabs.net>,
        "'e@...24.org'" <e@...24.org>,
        "'jbaron@...mai.com'" <jbaron@...mai.com>,
        "'linux-fsdevel@...r.kernel.org'" <linux-fsdevel@...r.kernel.org>,
        "'linux-aio@...ck.org'" <linux-aio@...ck.org>,
        "'omar.kilani@...il.com'" <omar.kilani@...il.com>,
        "'tglx@...utronix.de'" <tglx@...utronix.de>,
        'Al Viro' <viro@...IV.linux.org.uk>,
        'Linus Torvalds' <torvalds@...ux-foundation.org>,
        "'linux-arch@...r.kernel.org'" <linux-arch@...r.kernel.org>
Subject: RE: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask

From: Eric W. Biederman
> Sent: 12 June 2019 13:56
> David Laight <David.Laight@...LAB.COM> writes:
> 
> > From: David Laight
> >> Sent: 11 June 2019 10:52
> > ...
> >> If I have an application that has a loop with a pselect call that
> >> enables SIGINT (without a handler) and, for whatever reason,
> >> one of the fd is always 'ready' then I'd expect a SIGINT
> >> (from ^C) to terminate the program.
> >>
> >> A quick test program:
> >>
> >> #include <sys/time.h>
> >> #include <sys/types.h>
> >> #include <unistd.h>
> >>
> >> #include <sys/select.h>
> >> #include <signal.h>
> >>
> >> int main(int argc, char **argv)
> >> {
> >>         fd_set readfds;
> >>         sigset_t sig_int;
> >>         struct timespec delay = {1, 0};
> >>
> >>         sigfillset(&sig_int);
> >>         sigdelset(&sig_int, SIGINT);
> >>
> >>         sighold(SIGINT);
> >>
> >>         for (;;) {
> >>                 FD_ZERO(&readfds);
> >>                 FD_SET(0, &readfds);
> >>                 pselect(1, &readfds, NULL, NULL, &delay, &sig_int);
> >>
> >>                 poll(0,0,1000);
> >>         }
> >> }
> >>
> >> Run under strace to see what is happening and send SIGINT from a different terminal.
> >> The program sleeps for a second in each of the pselect() and poll() calls.
> >> Send a SIGINT and in terminates after pselect() returns ERESTARTNOHAND.
> >>
> >> Run again, this time press enter - making fd 0 readable.
> >> pselect() returns 1, but the program still exits.
> >> (Tested on a 5.1.0-rc5 kernel.)
> >>
> >> If a signal handler were defined it should be called instead.
> >
> > If I add a signal handler for SIGINT it is called when pselect()
> > returns regardless of the return value.
> 
> That is odd.  Is this with Oleg's fix applied?

No it is a 5.1.0-rc5 kernel with no related local patches.
So it is the 'historic' behaviour of pselect().
But not the original one! Under 2.6.22-5-31 the signal handler isn't caller
when pselect() returns 1.

	David

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