Messages in this thread | | | From | Andrey Mirkin <> | Subject | Re: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process | Date | Wed, 22 Oct 2008 14:12:12 +0400 |
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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.
Andrey
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