linux-kernel - Re: [PATCH v2] signal: Adjust error codes according to restore_user

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Message-Id: <B9F0F146-C687-4D1D-8BFF-1236564631F6@gmail.com>
Date:   Tue, 28 May 2019 04:37:46 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        "dbueso@...e.de" <dbueso@...e.de>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        Davidlohr Bueso <dave@...olabs.net>, Eric Wong <e@...24.org>,
        Jason Baron <jbaron@...mai.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>,
        Omar Kilani <omar.kilani@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] signal: Adjust error codes according to restore_user_sigmask()



> On May 28, 2019, at 2:12 AM, David Laight <David.Laight@...lab.com> wrote:
> 
> From: Deepa Dinamani
>> Sent: 24 May 2019 18:02
> ...
>> Look at the code before 854a6ed56839a:
>> 
>> /*
>>       * If we changed the signal mask, we need to restore the original one.
>>       * In case we've got a signal while waiting, we do not restore the
>>       * signal mask yet, and we allow do_signal() to deliver the signal on
>>       * the way back to userspace, before the signal mask is restored.
>>       */
>>      if (sigmask) {
>>             ####### This err has not been changed since ep_poll()
>>             ####### So if there is a signal before this point, but
>> err = 0, then we goto else.
>>              if (err == -EINTR) {
>>                      memcpy(&current->saved_sigmask, &sigsaved,
>>                             sizeof(sigsaved));
>>                      set_restore_sigmask();
>>              } else
>>                    ############ This is a problem if there is signal
>> pending that is sigmask should block.
>>                    ########### This is the whole reason we have
>> current->saved_sigmask?
>>                      set_current_blocked(&sigsaved);
>>      }
> 
> What happens if all that crap is just deleted (I presume from the
> bottom of ep_wait()) ?

Hmm, you have to update the saved_sigmask or the sigmask.

> I'm guessing that on the way back to userspace signal handlers for
> signals enabled in the process's current mask (the one specified
> to epoll_pwait) get called.
> Then the signal mask is loaded from current->saved_sigmask and
> and enabled signal handlers are called again.

Who is saving this saved_sigmask that is being restored on the way back?

> No special code there that depends on the syscall result, errno
> of the syscall number.

I didn’t say this has anything to do with errno.

-Deepa