linux-kernel - Re: [PATCH] x86/smp: Fix cpuN startup panic

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Date:	Wed, 08 Aug 2012 07:20:08 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	Jiang Liu <liuj97@...il.com>
Cc:	"Chen, LinX Z" <linx.z.chen@...el.com>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	hpa@...or.com
Subject: Re: [PATCH] x86/smp: Fix cpuN startup panic

On Wed, 2012-08-08 at 00:33 +0800, Jiang Liu wrote:
> On 08/07/2012 05:50 PM, Chen, LinX Z wrote:
> > From: Lin Chen <linx.z.chen@...el.com>
> > 
> > We hit a panic while doing cpu hotplug test.
> > <0>[  627.982857] Kernel panic - not syncing: smp_callin: CPU1 started up but did not get a callout!
> > <0>[  627.982864]
> > <4>[  627.982876] Pid: 0, comm: kworker/0:1 Tainted: G ...
> > <4>[  627.982883] Call Trace:
> > <4>[  627.982903]  [<c18f2977>] panic+0x66/0x16c
> > <4>[  627.982918]  [<c12234cc>] ? default_get_apic_id+0x1c/0x40
> > <4>[  627.982931]  [<c18ef96d>] start_secondary+0xda/0x252
> > 
> > During BSP bootup AP, it is possible that BSP be preempted before
> > finishing STARTUP sequence of AP(set cpu_callout_mask) which maybe cause
> > AP busy wait for it. At present, AP will wait for 2 seconds then panic.
> > 
> > This patch let AP waits until BSP finish the startup sequence and gives
> > WARNING when BSP is preempted more than 2 seconds.
> > 
> > Signed-off-by: Yanmin Zhang <yanmin_zhang@...ux.intel.com>
> > Signed-off-by: Lin Chen <linx.z.chen@...el.com>
> > ---
> >  arch/x86/kernel/smpboot.c |   11 ++++++-----
> >  1 files changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> > index 7c5a8c3..a9e3379 100644
> > --- a/arch/x86/kernel/smpboot.c
> > +++ b/arch/x86/kernel/smpboot.c
> > @@ -165,19 +165,20 @@ static void __cpuinit smp_callin(void)
> >       * Waiting 2s total for startup (udelay is not yet working)
> >       */
> >      timeout = jiffies + 2*HZ;
> > -    while (time_before(jiffies, timeout)) {
> > +    while (1) {
> Hi Yanmin,
> 
> 	Seems a little risky, what if a slave CPU can't be booted due to hardware errors?
Slave CPU runs the loop. Basically, there is a handshake between BSP and AP.
The patch doesn't change BSP codes. So when slave CPU fails, BSP still goes ahead
and kernel still works.
 
> 	Regards!
> 	Gerry
> 
> >          /*
> >           * Has the boot CPU finished it's STARTUP sequence?
> >           */
> >          if (cpumask_test_cpu(cpuid, cpu_callout_mask))
> >              break;
> >          cpu_relax();
> > +        if (!time_before(jiffies, timeout)) {
> > +            WARN(1, "%s: CPU%d started up but did not get a callout!\n",
> > +                    __func__, cpuid);
> > +            timeout = jiffies + 2*HZ;
> > +        }
> >      }
> > 
> > -    if (!time_before(jiffies, timeout)) {
> > -        panic("%s: CPU%d started up but did not get a callout!\n",
> > -              __func__, cpuid);
> > -    }
> > 
> >      /*
> >       * the boot CPU has finished the init stage and is spinning
> 


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