Message-ID: <48FF45CF.5000306@cs.columbia.edu>
Date: Wed, 22 Oct 2008 11:25:03 -0400
From: Oren Laadan <orenl@cs.columbia.edu>
Organization: Columbia University
User-Agent: Thunderbird 2.0.0.16 (X11/20080707)
MIME-Version: 1.0
To: Andrey Mirkin <major@openvz.org>
CC: Louis.Rilling@kerlabs.com, containers@lists.linux-foundation.org,
       Cedric Le Goater <clg@fr.ibm.com>, linux-kernel@vger.kernel.org,
       Pavel Emelyanov <xemul@openvz.org>
Subject: Re: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process
References: <1224285098-573-1-git-send-email-major@openvz.org>	<200810221249.55600.major@openvz.org>	<20081022092502.GW15171@hawkmoon.kerlabs.com> <200810221412.14174.major@openvz.org>
In-Reply-To: <200810221412.14174.major@openvz.org>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2863
Lines: 84


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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/