linux-kernel - Re: [PATCH]: xen: fix too early kmalloc call

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Message-ID: <20090112144653.GB14016@elte.hu>
Date:	Mon, 12 Jan 2009 15:46:53 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Mike Travis <travis@....com>,
	Christophe Saout <christophe@...ut.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]: xen: fix too early kmalloc call


* Johannes Weiner <hannes@...xchg.org> wrote:

> On Mon, Jan 12, 2009 at 09:53:02AM +0100, Ingo Molnar wrote:
> > 
> > * Mike Travis <travis@....com> wrote:
> > 
> > > Subject: xen: fix too early kmalloc call
> > > 
> > > From: Christophe Saout <christophe@...ut.de> 
> > > 
> > > Impact: fixes bootup of xen.
> > > 
> > > Christophe reported the following problem:
> > > 
> > > >  (basically it seems that SLAB is not yet up, with earlyprintk it is
> > > >  giving me an Oops in __kmalloc before)
> > > 
> > > Replace call to kmalloc with alloc_bootmem.
> > > 
> > > Also from Christophe:
> > > > (me)
> > > > > Or I could copy the text and submit it as a new patch?
> > > >
> > > > Yes, I would prefer that.  Also, my commit message was not really
> > > > following Kernel standards and it's only a very simple change.
> > > 
> > > Signed-off-by: Mike Travis <travis@....com>
> > 
> > i've applied the fix to tip/cpus4096, in the form below.
> > 
> > Please submit clean log messages. Your commit description was confused - 
> > the patch is From: Christophe, but the message talks about Christophe in 
> > the third person. Also, it included conversational bits that have no 
> > value for the Git history.
> > 
> > 	Ingo
> > 
> > -------------------->
> > >>From 28e08861b9afab4168b758fb7b95aa7a4da0f668 Mon Sep 17 00:00:00 2001
> > From: Christophe Saout <christophe@...ut.de>
> > Date: Sun, 11 Jan 2009 11:46:23 -0800
> > Subject: [PATCH] xen: fix too early kmalloc call
> > 
> > Impact: fix bootup crash on xen guests
> > 
> > SLAB is not yet up, with earlyprintk it is giving me an Oops in __kmalloc.
> > 
> > Replace call to kmalloc() with alloc_bootmem().
> > 
> > Reported-by: Christophe Saout <christophe@...ut.de>
> > Signed-off-by: Mike Travis <travis@....com>
> > Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > ---
> >  drivers/xen/events.c |    5 +++--
> >  1 files changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> > index ed7527b..3141e14 100644
> > --- a/drivers/xen/events.c
> > +++ b/drivers/xen/events.c
> > @@ -26,6 +26,7 @@
> >  #include <linux/irq.h>
> >  #include <linux/module.h>
> >  #include <linux/string.h>
> > +#include <linux/bootmem.h>
> >  
> >  #include <asm/ptrace.h>
> >  #include <asm/irq.h>
> > @@ -831,8 +832,8 @@ void __init xen_init_IRQ(void)
> >  	int i;
> >  	size_t size = nr_cpu_ids * sizeof(struct cpu_evtchn_s);
> >  
> > -	cpu_evtchn_mask_p = kmalloc(size, GFP_KERNEL);
> > -	BUG_ON(cpu_evtchn_mask == NULL);
> > +	cpu_evtchn_mask_p = alloc_bootmem(size);
> > +	BUG_ON(cpu_evtchn_mask_p == NULL);
> 
> Impossible condition :-) alloc_bootmem() crashes before you could catch 
> it here.

yeah ... but that's just a current behavior of bootmem. It's always 
prudent to check for allocation errors.

	Ingo
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