linux-kernel - Re: [PATCH respin, was PATCH for review] During VM oom condition, kill all threads in process group

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Message-Id: <1185893751.22717.36.camel@farscape.rchland.ibm.com>
Date:	Tue, 31 Jul 2007 09:55:51 -0500
From:	Will Schmidt <will_schmidt@...t.ibm.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH respin, was PATCH for review] During VM oom condition,
	kill all threads in process group

On Tue, 2007-07-31 at 11:31 +0200, Pavel Machek wrote:
> Hi!
> 
> > 
> > During VM oom condition, kill all threads in process group.
> > 
> > We have had complaints where a threaded application is left in a bad
> > state after one of it's threads is killed when we hit a VM: out_of_memory
> > condition.
> > Killing just one of the process threads can leave the application in a
> > bad state, whereas killing the entire process group would allow for
> > the application to restart, or be otherwise handled, and makes it very
> > obvious that something has gone wrong.
> > 
> > This change allows the entire process group to be taken down, rather
> > than just the one thread.
> > 
> > Signed-off-by: Will Schmidt <will_schmidt@...t.ibm.com>
> 
> > diff --git a/arch/sparc64/mm/fault.c b/arch/sparc64/mm/fault.c
> > index 17123e9..13fdfa3 100644
> > --- a/arch/sparc64/mm/fault.c
> > +++ b/arch/sparc64/mm/fault.c
> > @@ -466,7 +466,7 @@ out_of_memory:
> >  	up_read(&mm->mmap_sem);
> >  	printk("VM: killing process %s\n", current->comm);
> >  	if (!(regs->tstate & TSTATE_PRIV))
> > -		do_exit(SIGKILL);
> > +		do_group_exit(SIGKILL);
> >  	goto handle_kernel_fault;
> >  
> >  intr_or_no_mm:
> 
> is the printk still accurate (does it kill more than one process now)?

I was going to double-check this morning.. but don't see where
current->comm is copied into a new task_struct.  I thought that all
processes within the group had the same current->comm value, so figure
this is OK.  

> Why does it print when it will not really kill the process?
no idea..  

> I see similar code across all the archs... would it make sense to
> create common helper... or is the helper too trivial?

The checks blocking flow into do_group_exit, like (regs->tstate &
TSTATE_PRIV) for sparc64, or (user_mode(regs)) for powerpc, do vary
across the arch's.    The code could be rearranged to have a helper
containing just the printk and the do_group_exit() call; but I'm not
sure that would be an improvement. 

maybe a    do_group_sigkill_if(condition); helper    :-)


-Will 

> 									Pavel

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