linux-kernel - Re: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process

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Date:	Thu, 23 Oct 2008 06:57:57 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Andrey Mirkin <amirkin@...allels.com>
Cc:	Oren Laadan <orenl@...columbia.edu>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Louis.Rilling@...labs.com,
	Cedric Le Goater <clg@...ibm.com>,
	Andrey Mirkin <major@...nvz.org>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [Devel] Re: [PATCH 08/10] Introduce functions to restart a
	process

On Thu, 2008-10-23 at 13:00 +0400, Andrey Mirkin wrote:
> 
> > >>> It is not related to the freezer code actually.
> > >>> That is needed to restart syscalls. Right now I don't have a code in my
> > >>> patchset which restarts a syscall, but later I plan to add it.
> > >>> In OpenVZ checkpointing we restart syscalls if process was caught in
> > >>> syscall during checkpointing.
> > >>
> > >> Do you checkpoint uninterruptible syscalls as well? If only
> > >> interruptible syscalls are checkpointed, I'd say that either this
> > >> syscall uses ERESTARTSYS or ERESTART_RESTARTBLOCK, and then signal
> > >> handling code already does the trick, or this syscall does not restart
> > >> itself when interrupted, and well, this is life, userspace just sees
> > >> -EINTR, which is allowed by the syscall spec.
> > >> Actually this is how we checkpoint/migrate tasks in interruptible
> > >> syscalls in Kerrighed and this works.
> > >
> > > We checkpoint only interruptible syscalls. Some syscalls do not restart
> > > themself, that is why after restarting a process we restart syscall to
> > > complete it.
> >
> > Can you please elaborate on this ?  I don't recall having had issues
> > with that.
> 
> Right now in 2.6.18 kernel we restarts in such a way pause, rt_sigtimedwait 
> and futex syscalls. Recently futex syscall was reworked and we will not need 
> such hooks for it.

Could you elaborate on this a bit?

If the futex syscall was reworked, perhaps we can do the same for
rt_sigtimedwait() and get rid of this code completely.

-- Dave

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