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SubjectRe: [PATCH] x86/smp: Fix cpuN startup panic
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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@intel.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@linux.intel.com>
> > Signed-off-by: Lin Chen <linx.z.chen@intel.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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