lkml.org 
[lkml]   [2008]   [Oct]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process
Date
On Wednesday 22 October 2008 19:25 Oren Laadan wrote:
> Andrey Mirkin wrote:
> > On Wednesday 22 October 2008 13:25 Louis Rilling wrote:
> >> On Wed, Oct 22, 2008 at 12:49:54PM +0400, Andrey Mirkin wrote:
> >>> On Monday 20 October 2008 13:23 Cedric Le Goater wrote:
> >>>> Hello Andrey !
> >>>>
> >>>>> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
> >>>>> index 109792b..a4848a3 100644
> >>>>> --- a/arch/x86/kernel/entry_32.S
> >>>>> +++ b/arch/x86/kernel/entry_32.S
> >>>>> @@ -225,6 +225,7 @@ ENTRY(ret_from_fork)
> >>>>> GET_THREAD_INFO(%ebp)
> >>>>> popl %eax
> >>>>> CFI_ADJUST_CFA_OFFSET -4
> >>>>> +ret_from_fork_tail:
> >>>>> pushl $0x0202 # Reset kernel eflags
> >>>>> CFI_ADJUST_CFA_OFFSET 4
> >>>>> popfl
> >>>>> @@ -233,6 +234,26 @@ ENTRY(ret_from_fork)
> >>>>> CFI_ENDPROC
> >>>>> END(ret_from_fork)
> >>>>>
> >>>>> +ENTRY(i386_ret_from_resume)
> >>>>> + CFI_STARTPROC
> >>>>> + pushl %eax
> >>>>> + CFI_ADJUST_CFA_OFFSET 4
> >>>>> + call schedule_tail
> >>>>> + GET_THREAD_INFO(%ebp)
> >>>>> + popl %eax
> >>>>> + CFI_ADJUST_CFA_OFFSET -4
> >>>>> + movl (%esp), %eax
> >>>>> + testl %eax, %eax
> >>>>> + jz 1f
> >>>>> + pushl %esp
> >>>>> + call *%eax
> >>>>> + addl $4, %esp
> >>>>> +1:
> >>>>> + addl $256, %esp
> >>>>> + jmp ret_from_fork_tail
> >>>>> + CFI_ENDPROC
> >>>>> +END(i386_ret_from_resume)
> >>>>
> >>>> Could you explain why you need to do this
> >>>>
> >>>> call *%eax
> >>>>
> >>>> is it related to the freezer code ?
> >>>
> >>> 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.

Andrey


\
 
 \ /
  Last update: 2008-10-23 11:05    [from the cache]
©2003-2011 Jasper Spaans