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    SubjectRe: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process


    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.

    Thanks,

    Oren.

    >
    > Andrey
    > _______________________________________________
    > Containers mailing list
    > Containers@lists.linux-foundation.org
    > https://lists.linux-foundation.org/mailman/listinfo/containers


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