Re: [PATCH 3/9] xen/time: Fix kasprintf splat when allocating timer%d IRQ line.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Apr 26, 2013 at 05:11:35PM +0100, Stefano Stabellini wrote:
> On Tue, 16 Apr 2013, Konrad Rzeszutek Wilk wrote:
> > When we online the CPU, we get this splat:
> > 
> > smpboot: Booting Node 0 Processor 1 APIC 0x2
> > installing Xen timer for CPU 1
> > BUG: sleeping function called from invalid context at /home/konrad/ssd/konrad/linux/mm/slab.c:3179
> > in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/1
> > Pid: 0, comm: swapper/1 Not tainted 3.9.0-rc6upstream-00001-g3884fad #1
> > Call Trace:
> >  [<ffffffff810c1fea>] __might_sleep+0xda/0x100
> >  [<ffffffff81194617>] __kmalloc_track_caller+0x1e7/0x2c0
> >  [<ffffffff81303758>] ? kasprintf+0x38/0x40
> >  [<ffffffff813036eb>] kvasprintf+0x5b/0x90
> >  [<ffffffff81303758>] kasprintf+0x38/0x40
> >  [<ffffffff81044510>] xen_setup_timer+0x30/0xb0
> >  [<ffffffff810445af>] xen_hvm_setup_cpu_clockevents+0x1f/0x30
> >  [<ffffffff81666d0a>] start_secondary+0x19c/0x1a8
> > 
> > The solution to that is use kasprintf in the CPU hotplug path
> > that 'online's the CPU. That is, do it in in xen_hvm_cpu_notify,
> > and remove the call to in xen_hvm_setup_cpu_clockevents.
> > 
> > Unfortunatly the later is not a good idea as the bootup path
> > does not use xen_hvm_cpu_notify so we would end up never allocating
> > timer%d interrupt lines when booting. As such add the check for
> > atomic() to continue.
> 
> This last is not reflected in the code.

I found out that it was not needed.
> 
> Also, is it actually OK to move xen_setup_timer out of
> xen_hvm_setup_cpu_clockevents?

Yes. It ends up being called earlier - in the notifier.
> 
> xen_setup_cpu_clockevents registers xen_clock_events as clocksource and
> xen_clock_events is setup by xen_setup_timer so we need to make sure
> that the call order remains the same.

The order is still the same.
> 
> 
> > CC: stable@vger.kernel.org
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > ---
> >  arch/x86/xen/enlighten.c | 5 ++++-
> >  arch/x86/xen/time.c      | 6 +++++-
> >  2 files changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > index 47d3243..ddbd54a 100644
> > --- a/arch/x86/xen/enlighten.c
> > +++ b/arch/x86/xen/enlighten.c
> > @@ -1641,8 +1641,11 @@ static int __cpuinit xen_hvm_cpu_notify(struct notifier_block *self,
> >  	switch (action) {
> >  	case CPU_UP_PREPARE:
> >  		xen_vcpu_setup(cpu);
> > -		if (xen_have_vector_callback)
> > +		if (xen_have_vector_callback) {
> >  			xen_init_lock_cpu(cpu);
> > +			if (xen_feature(XENFEAT_hvm_safe_pvclock))
> > +				xen_setup_timer(cpu);
> > +		}
> >  		break;
> >  	default:
> >  		break;
> > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> > index 0296a95..054cc01 100644
> > --- a/arch/x86/xen/time.c
> > +++ b/arch/x86/xen/time.c
> > @@ -497,7 +497,11 @@ static void xen_hvm_setup_cpu_clockevents(void)
> >  {
> >  	int cpu = smp_processor_id();
> >  	xen_setup_runstate_info(cpu);
> > -	xen_setup_timer(cpu);
> > +	/*
> > +	 * xen_setup_timer(cpu) - snprintf is bad in atomic context. Hence
> > +	 * doing it xen_hvm_cpu_notify (which gets called by smp_init during
> > +	 * early bootup and also during CPU hotplug events).
> > +	 */
> >  	xen_setup_cpu_clockevents();
> >  }
> >  
> > -- 
> > 1.8.1.4
> >