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

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Date:   Wed, 12 Jun 2019 07:55:51 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Oleg Nesterov' <oleg@...hat.com>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        'Deepa Dinamani' <deepa.kernel@...il.com>,
        "'linux-kernel\@vger.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'arnd\@arndb.de'" <arnd@...db.de>,
        "'dbueso\@suse.de'" <dbueso@...e.de>,
        "'axboe\@kernel.dk'" <axboe@...nel.dk>,
        "'dave\@stgolabs.net'" <dave@...olabs.net>,
        "'e\@80x24.org'" <e@...24.org>,
        "'jbaron\@akamai.com'" <jbaron@...mai.com>,
        "'linux-fsdevel\@vger.kernel.org'" <linux-fsdevel@...r.kernel.org>,
        "'linux-aio\@kvack.org'" <linux-aio@...ck.org>,
        "'omar.kilani\@gmail.com'" <omar.kilani@...il.com>,
        "'tglx\@linutronix.de'" <tglx@...utronix.de>,
        'Al Viro' <viro@...IV.linux.org.uk>,
        'Linus Torvalds' <torvalds@...ux-foundation.org>,
        "'linux-arch\@vger.kernel.org'" <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask

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?

Eric