From: David Laight <David.Laight@ACULAB.COM> To: 'Oleg Nesterov' <oleg@redhat.com> Cc: "'Eric W. Biederman'" <ebiederm@xmission.com>, 'Andrew Morton' <akpm@linux-foundation.org>, 'Deepa Dinamani' <deepa.kernel@gmail.com>, "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>, "'arnd@arndb.de'" <arnd@arndb.de>, "'dbueso@suse.de'" <dbueso@suse.de>, "'axboe@kernel.dk'" <axboe@kernel.dk>, "'dave@stgolabs.net'" <dave@stgolabs.net>, "'e@80x24.org'" <e@80x24.org>, "'jbaron@akamai.com'" <jbaron@akamai.com>, "'linux-fsdevel@vger.kernel.org'" <linux-fsdevel@vger.kernel.org>, "'linux-aio@kvack.org'" <linux-aio@kvack.org>, "'omar.kilani@gmail.com'" <omar.kilani@gmail.com>, "'tglx@linutronix.de'" <tglx@linutronix.de>, 'Al Viro' <viro@ZenIV.linux.org.uk>, 'Linus Torvalds' <torvalds@linux-foundation.org>, "'linux-arch@vger.kernel.org'" <linux-arch@vger.kernel.org> Subject: RE: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask Date: Thu, 13 Jun 2019 08:48:41 +0000 [thread overview] Message-ID: <6e9b964b08d84c99980b1707e5fe3d1d@AcuMS.aculab.com> (raw) In-Reply-To: <6f748b26bef748208e2a74174c0c0bfc@AcuMS.aculab.com> From: David Laight > Sent: 12 June 2019 15:18 > From: Oleg Nesterov > > Sent: 12 June 2019 14:46 > > On 06/11, David Laight wrote: > > > > > > 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. > > > > This was never true. > > > > Before Eric's patches SIGINT can kill a process or not, depending on timing. > > In particular, if SIGINT was already pending before pselect() and it finds > > an already ready fd, the program won't terminate. > > Which matches what I see on a very old Linux system. > > > After the Eric's patches SIGINT will only kill the program if pselect() does > > not find a ready fd. > > > > And this is much more consistent. Now we can simply say that the signal will > > be delivered only if pselect() fails and returns -EINTR. If it doesn't have > > a handler the process will be killed, otherwise the handler will be called. > > But is it what the standards mandate? > Can anyone check how Solaris and any of the BSDs behave? > I don't have access to any solaris systems (I doubt I'll get the disk to > spin on the one in my garage). > I can check NetBSD when I get home. I tested NetBSD last night. pselect() always calls the signal handlers even when an fd is ready. I'm beginning to suspect that this is the 'standards conforming' behaviour. I don't remember when pselect() was added to the ToG specs, it didn't go through XNET while I was going to the meetings. David > > The ToG page for pselect() http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html > says: > "If sigmask is not a null pointer, then the pselect() function shall replace > the signal mask of the caller by the set of signals pointed to by sigmask > before examining the descriptors, and shall restore the signal mask of the > calling thread before returning." > Note that it says 'before examining the descriptors' not 'before blocking'. > Under the general description about signals it also says that the signal handler > will be called (or other action happen) when a pending signal is unblocked. > So unblocking SIGINT (set to SIG_DFL) prior to examining the descriptors > should be enough to cause the process to exit. > The fact that signal handlers are not called until 'return to user' > is really an implementation choice - but (IMHO) it should appear as if they > were called at the time they became unmasked. > > If nothing else the man pages need a note about the standards and portability. > > David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight@ACULAB.COM> To: 'Oleg Nesterov' <oleg@redhat.com> Cc: "'Eric W. Biederman'" <ebiederm@xmission.com>, 'Andrew Morton' <akpm@linux-foundation.org>, 'Deepa Dinamani' <deepa.kernel@gmail.com>, "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>, "'arnd@arndb.de'" <arnd@arndb.de>, "'dbueso@suse.de'" <dbueso@suse.de>, "'axboe@kernel.dk'" <axboe@kernel.dk>, "'dave@stgolabs.net'" <dave@stgolabs.net>, "'e@80x24.org'" <e@80x24.org>, "'jbaron@akamai.com'" <jbaron@akamai.com>, "'linux-fsdevel@vger.kernel.org'" <linux-fsdevel@vger.kernel.org>, "'linux-aio@kvack.org'" <linux-aio@kvack.org>, "'omar.kilani@gmail.com'" <omar.kilani@gmail.com>, "'tglx@linutronix.de'" <tglx@linutronix.de>, 'Al Viro' <viro@ZenIV.linux.org.uk>, 'Linus Torvalds' <torvalds@linux-foundation.org>, "'linux-arch@vger.kernel.org'" <linux-arch@vger.kernel.org> Subject: RE: [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask Date: Thu, 13 Jun 2019 08:48:41 +0000 [thread overview] Message-ID: <6e9b964b08d84c99980b1707e5fe3d1d@AcuMS.aculab.com> (raw) In-Reply-To: <6f748b26bef748208e2a74174c0c0bfc@AcuMS.aculab.com> From: David Laight > Sent: 12 June 2019 15:18 > From: Oleg Nesterov > > Sent: 12 June 2019 14:46 > > On 06/11, David Laight wrote: > > > > > > 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. > > > > This was never true. > > > > Before Eric's patches SIGINT can kill a process or not, depending on timing. > > In particular, if SIGINT was already pending before pselect() and it finds > > an already ready fd, the program won't terminate. > > Which matches what I see on a very old Linux system. > > > After the Eric's patches SIGINT will only kill the program if pselect() does > > not find a ready fd. > > > > And this is much more consistent. Now we can simply say that the signal will > > be delivered only if pselect() fails and returns -EINTR. If it doesn't have > > a handler the process will be killed, otherwise the handler will be called. > > But is it what the standards mandate? > Can anyone check how Solaris and any of the BSDs behave? > I don't have access to any solaris systems (I doubt I'll get the disk to > spin on the one in my garage). > I can check NetBSD when I get home. I tested NetBSD last night. pselect() always calls the signal handlers even when an fd is ready. I'm beginning to suspect that this is the 'standards conforming' behaviour. I don't remember when pselect() was added to the ToG specs, it didn't go through XNET while I was going to the meetings. David > > The ToG page for pselect() http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html > says: > "If sigmask is not a null pointer, then the pselect() function shall replace > the signal mask of the caller by the set of signals pointed to by sigmask > before examining the descriptors, and shall restore the signal mask of the > calling thread before returning." > Note that it says 'before examining the descriptors' not 'before blocking'. > Under the general description about signals it also says that the signal handler > will be called (or other action happen) when a pending signal is unblocked. > So unblocking SIGINT (set to SIG_DFL) prior to examining the descriptors > should be enough to cause the process to exit. > The fact that signal handlers are not called until 'return to user' > is really an implementation choice - but (IMHO) it should appear as if they > were called at the time they became unmasked. > > If nothing else the man pages need a note about the standards and portability. > > David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: <a href=mailto:"aart@kvack.org">aart@kvack.org</a>
next prev parent reply other threads:[~2019-06-13 16:01 UTC|newest] Thread overview: 155+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-05-22 3:21 [PATCH v2] signal: Adjust error codes according to restore_user_sigmask() Deepa Dinamani 2019-05-22 15:05 ` Oleg Nesterov 2019-05-22 15:55 ` Deepa Dinamani 2019-05-22 16:14 ` Oleg Nesterov 2019-05-22 16:33 ` Deepa Dinamani 2019-05-23 9:03 ` David Laight 2019-05-23 14:59 ` Oleg Nesterov 2019-05-23 16:18 ` David Laight 2019-05-23 16:36 ` Oleg Nesterov 2019-05-23 16:56 ` David Laight 2019-05-23 18:06 ` Deepa Dinamani 2019-05-23 20:41 ` Deepa Dinamani 2019-05-23 21:06 ` Deepa Dinamani 2019-05-24 9:58 ` David Laight 2019-05-24 14:10 ` Oleg Nesterov 2019-05-24 15:16 ` Deepa Dinamani 2019-05-24 16:33 ` Oleg Nesterov 2019-05-24 17:01 ` Deepa Dinamani 2019-05-27 15:04 ` Oleg Nesterov 2019-05-28 20:47 ` Deepa Dinamani 2019-05-29 16:57 ` Oleg Nesterov 2019-05-29 18:42 ` Deepa Dinamani 2019-05-28 9:02 ` David Laight 2019-05-28 9:12 ` David Laight 2019-05-28 11:37 ` Deepa Dinamani 2019-05-28 12:04 ` David Laight 2019-05-24 14:19 ` Oleg Nesterov 2019-05-24 14:29 ` Deepa Dinamani 2019-05-24 14:51 ` Oleg Nesterov 2019-05-24 13:29 ` Oleg Nesterov 2019-05-24 14:59 ` David Laight 2019-05-24 15:09 ` David Laight 2019-05-24 15:46 ` Oleg Nesterov 2019-05-24 15:44 ` Oleg Nesterov 2019-05-24 16:40 ` David Laight 2019-05-23 14:33 ` Oleg Nesterov 2019-05-22 22:18 ` Chris Down 2019-05-22 22:52 ` Deepa Dinamani 2019-05-22 22:52 ` Deepa Dinamani 2019-05-29 16:11 ` pselect/etc semantics (Was: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask()) Oleg Nesterov 2019-05-29 16:54 ` David Laight 2019-05-29 18:50 ` Eric Wong 2019-05-30 9:34 ` David Laight 2019-05-30 13:04 ` pselect/etc semantics Eric W. Biederman 2019-05-29 16:56 ` pselect/etc semantics (Was: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask()) Deepa Dinamani 2019-05-29 18:26 ` Deepa Dinamani 2019-05-29 22:32 ` Arnd Bergmann 2019-05-30 1:54 ` pselect/etc semantics Eric W. Biederman 2019-05-30 18:28 ` Arnd Bergmann 2019-05-30 14:40 ` pselect/etc semantics (Was: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask()) Oleg Nesterov 2019-05-30 18:37 ` Arnd Bergmann 2019-05-30 13:01 ` pselect/etc semantics Eric W. Biederman 2019-05-30 15:18 ` David Laight 2019-05-30 16:13 ` Oleg Nesterov 2019-05-30 15:38 ` Eric W. Biederman 2019-05-30 15:48 ` Deepa Dinamani 2019-05-30 16:59 ` Deepa Dinamani 2019-05-30 16:08 ` Oleg Nesterov 2019-05-30 17:20 ` Eric W. Biederman 2019-05-30 16:22 ` David Laight 2019-05-30 15:57 ` Oleg Nesterov 2019-05-30 21:03 ` Eric Wong 2019-06-04 13:41 ` [PATCH] signal: remove the wrong signal_pending() check in restore_user_sigmask() Oleg Nesterov 2019-06-04 15:31 ` Eric W. Biederman 2019-06-04 15:31 ` Eric W. Biederman 2019-06-04 15:57 ` David Laight 2019-06-04 15:57 ` David Laight 2019-06-04 16:37 ` Arnd Bergmann 2019-06-04 18:14 ` Deepa Dinamani 2019-06-04 18:35 ` Eric Wong 2019-06-04 21:26 ` Linus Torvalds 2019-06-04 22:24 ` Eric Wong 2019-06-04 23:51 ` Eric W. Biederman 2019-06-05 9:04 ` Oleg Nesterov 2019-06-05 8:56 ` Oleg Nesterov 2019-06-05 9:02 ` David Laight 2019-06-05 9:25 ` Oleg Nesterov 2019-06-05 9:58 ` David Laight 2019-06-05 15:58 ` [PATCH -mm 0/1] signal: simplify set_user_sigmask/restore_user_sigmask Oleg Nesterov 2019-06-05 15:58 ` [PATCH -mm 1/1] " Oleg Nesterov 2019-06-06 0:14 ` kbuild test robot 2019-06-06 1:06 ` kbuild test robot 2019-06-06 7:25 ` Oleg Nesterov 2019-06-06 7:30 ` Sedat Dilek 2019-06-05 17:24 ` [PATCH -mm 0/1] " Linus Torvalds 2019-06-06 9:05 ` David Laight 2019-06-06 11:05 ` Oleg Nesterov 2019-06-06 11:29 ` David Laight 2019-06-06 12:41 ` Oleg Nesterov 2019-06-06 13:23 ` David Laight 2019-06-06 10:22 ` Oleg Nesterov 2019-06-06 11:32 ` [PATCH -mm V2 1/1] " Oleg Nesterov 2019-06-06 14:08 ` [PATCH 0/2] select: simplify the usage of restore_saved_sigmask_unless() Oleg Nesterov 2019-06-06 14:08 ` [PATCH 1/2] select: change do_poll() to return -ERESTARTNOHAND rather than -EINTR Oleg Nesterov 2019-06-07 18:05 ` Linus Torvalds 2019-06-06 14:09 ` [PATCH 2/2] select: shift restore_saved_sigmask_unless() into poll_select_copy_remaining() Oleg Nesterov 2019-06-07 21:39 ` [RFC PATCH 0/5]: Removing saved_sigmask Eric W. Biederman 2019-06-07 21:39 ` Eric W. Biederman 2019-06-07 21:41 ` [RFC PATCH 1/5] signal: Teach sigsuspend to use set_user_sigmask Eric W. Biederman 2019-06-07 21:41 ` Eric W. Biederman 2019-06-07 21:41 ` Eric W. Biederman 2019-06-07 22:07 ` Linus Torvalds 2019-06-07 22:07 ` Linus Torvalds 2019-06-10 16:22 ` Oleg Nesterov 2019-06-10 21:20 ` Eric W. Biederman 2019-06-11 9:52 ` David Laight 2019-06-11 11:14 ` David Laight 2019-06-12 12:55 ` Eric W. Biederman 2019-06-12 12:55 ` Eric W. Biederman 2019-06-12 12:55 ` Eric W. Biederman 2019-06-12 13:24 ` David Laight 2019-06-12 13:24 ` David Laight 2019-06-12 13:35 ` Oleg Nesterov 2019-06-12 13:35 ` Oleg Nesterov 2019-06-12 13:39 ` David Laight 2019-06-12 13:39 ` David Laight 2019-06-11 15:46 ` David Laight 2019-06-11 15:46 ` David Laight 2019-06-12 12:40 ` Eric W. Biederman 2019-06-12 12:40 ` Eric W. Biederman 2019-06-12 12:40 ` Eric W. Biederman 2019-06-12 13:45 ` Oleg Nesterov 2019-06-12 14:18 ` David Laight 2019-06-12 15:11 ` Eric W. Biederman 2019-06-12 15:11 ` Eric W. Biederman 2019-06-12 15:37 ` Oleg Nesterov 2019-06-12 15:37 ` Oleg Nesterov 2019-06-13 8:48 ` David Laight [this message] 2019-06-13 8:48 ` David Laight 2019-06-13 9:43 ` Oleg Nesterov 2019-06-13 9:43 ` Oleg Nesterov 2019-06-13 10:56 ` David Laight 2019-06-13 10:56 ` David Laight 2019-06-13 12:43 ` Oleg Nesterov 2019-06-13 12:43 ` Oleg Nesterov 2019-06-11 18:55 ` Oleg Nesterov 2019-06-11 19:02 ` Eric W. Biederman 2019-06-11 19:02 ` Eric W. Biederman 2019-06-12 8:39 ` David Laight 2019-06-12 13:09 ` Eric W. Biederman 2019-06-12 13:09 ` Eric W. Biederman 2019-06-12 13:09 ` Eric W. Biederman 2019-06-07 21:41 ` [RFC PATCH 2/5] signal/kvm: Stop using sigprocmask in kvm_sigset_(activate|deactivate) Eric W. Biederman 2019-06-07 21:41 ` Eric W. Biederman 2019-06-07 21:41 ` Eric W. Biederman 2019-06-07 21:42 ` [RFC PATCH 3/5] signal: Always keep real_blocked in sync with blocked Eric W. Biederman 2019-06-07 21:42 ` Eric W. Biederman 2019-06-07 21:42 ` Eric W. Biederman 2019-06-07 21:43 ` [RFC PATCH 4/5] signal: Remove saved_sigmask Eric W. Biederman 2019-06-07 21:43 ` Eric W. Biederman 2019-06-07 21:43 ` Eric W. Biederman 2019-06-07 21:44 ` [RFC PATCH 5/5] signal: Remove the unnecessary restore_sigmask flag Eric W. Biederman 2019-06-07 21:44 ` Eric W. Biederman 2019-06-07 21:44 ` Eric W. Biederman 2019-06-11 18:58 ` [RFC PATCH 0/5]: Removing saved_sigmask Oleg Nesterov
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