From: Oleg Nesterov <oleg@redhat.com>
To: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: David Laight <David.Laight@aculab.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Arnd Bergmann <arnd@arndb.de>, "dbueso@suse.de" <dbueso@suse.de>,
"axboe@kernel.dk" <axboe@kernel.dk>,
Davidlohr Bueso <dave@stgolabs.net>, Eric Wong <e@80x24.org>,
Jason Baron <jbaron@akamai.com>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
linux-aio <linux-aio@kvack.org>,
Omar Kilani <omar.kilani@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask()
Date: Fri, 24 May 2019 18:33:10 +0200 [thread overview]
Message-ID: <20190524163310.GG2655@redhat.com> (raw)
In-Reply-To: <CABeXuvqSzy+v=3Y5NnMmfob7bvuNkafmdDqoex8BVENN3atqZA@mail.gmail.com>
On 05/24, Deepa Dinamani wrote:
>
> On Fri, May 24, 2019 at 7:11 AM Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > On 05/23, Deepa Dinamani wrote:
> > >
> > > Ok, since there has been quite a bit of argument here, I will
> > > backtrack a little bit and maybe it will help us understand what's
> > > happening here.
> > > There are many scenarios being discussed on this thread:
> > > a. State of code before 854a6ed56839a
> >
> > I think everything was correct,
>
> There were 2 things that were wrong:
>
> 1. If an unblocked signal was received, after the ep_poll(), then the
> return status did not indicate that.
Yes,
> This is expected behavior
> according to man page. If this is indeed what is expected then the man
> page should note that signal will be delivered in this case and return
> code will still be 0.
>
> "EINTR
> The call was interrupted by a signal handler before either any of the
> requested events occurred or the timeout expired; see signal(7)."
and what do you think the man page could say?
This is obviously possible for any syscall, and we can't avoid this. A signal
can come right after syscall insn completes. The signal handler will be called
but this won't change $rax, user-space can see return code == 0 or anything else.
And this doesn't differ from the case when the signal comes before syscall returns.
> 2. The restoring of the sigmask is done right in the syscall part and
> not while exiting the syscall and if you get a blocked signal here,
> you will deliver this to userspace.
So I assume that this time you are talking about epoll_pwait() and not epoll_wait()...
And I simply can't understand you. But yes, if the original mask doesn't include
the pending signal it will be delivered while the syscall can return success/timout
or -EFAULT or anything.
This is correct, see above.
> > > b. State after 854a6ed56839a
> >
> > obviously buggy,
>
> Ok, then can you point out what specifically was wrong with
> 854a6ed56839a?
Cough. If nothing else the lost -EINTR?
> And, not how it could be more simple?
Well, I already sent the patch and after that I even showed you the code with the
patch applied. See https://lore.kernel.org/lkml/20190523143340.GA23070@redhat.com/
> > What you are saying looks very confusing to me, I will assume that you
> > meant something like
> >
> > - a signal SIG_XXX was blocked before sys_epoll_pwait() was called
> >
> > - sys_epoll_pwait(sigmask) unblocks SIG_XXX according to sigmask
> >
> > - sys_epoll_pwait() calls do_epoll_wait() which returns success
> >
> > - SIG_XXX comes after that and it is "never noticed"
> >
> > Yes. Everything is correct. And see my reply to David, SIG_XXX can even
> > come _before_ sys_epoll_pwait() was called.
>
> No, I'm talking about a signal that was not blocked.
OK, see above.
> > > So the question is does the userspace have to know about this signal
> > > or not.
> >
> > If userspace needs to know about SIG_XXX it should not block it, that is all.
>
> What should be the return value if a signal is detected after a fd completed?
Did you mean "if a signal is detected after a ready fd was already found" ?
In this case the return value should report success. But I have already lost,
this all looks irrelevant wrt to fix we need.
> > > What [b] does is to move the signal check closer to the restoration of
> > > the signal.
> >
> > FOR NO REASON, afaics (to simplify, lets forget the problem with the wrong
> > return value you are trying to fix).
>
> As I already pointed out, the restoring of the sigmask is done during
> the syscall and not while exiting the syscall and if you get a blocked
> signal here, you will deliver this to userspace.
>
> > And even if there were ANY reason to do this, note that (with or without this
> > fix) the signal_pending() check inside restore_user_sigmask() can NOT help,
> > simply because SIG_XXX can come right after this check.
>
> This I pointed out already that we should probably make this sequence atomic.
See above.
Oleg.
next prev parent reply other threads:[~2019-05-24 16:33 UTC|newest]
Thread overview: 95+ 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 [this message]
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
2019-05-29 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 15:57 ` 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
2019-06-11 18:58 ` Oleg Nesterov
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