[Fwd: [PATCH] x86/smp: Fix cpuN startup panic]

[Fwd: [PATCH] x86/smp: Fix cpuN startup panic]

[Yanmin Zhang]

Peter,

What's your opinion about the patch? We hit it when enabling Medfield Android mobile.
This patch would put AP to a loop.

Another method to fix it is just to enlarge the wait time, for example, from 2HZ to 10HZ.

Yanmin

-------- Forwarded Message --------
> From: Chen, LinX Z <linx.z.chen@intel.com>
> To: linux-kernel@vger.kernel.org
> Cc: mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com,
> yanmin_zhang@linux.intel.com
> Subject: [PATCH] x86/smp: Fix cpuN startup panic
> Date: Tue, 07 Aug 2012 18:50:40 +0900
> 
> 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) {
>   		/*
>   		 * 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
> -- 
> 1.7.1

Re: [Fwd: [PATCH] x86/smp: Fix cpuN startup panic]

[H. Peter Anvin]

On 08/09/2012 05:35 PM, Yanmin Zhang wrote:
> Peter,
>
> What's your opinion about the patch? We hit it when enabling Medfield Android mobile.
> This patch would put AP to a loop.
>
> Another method to fix it is just to enlarge the wait time, for example, from 2HZ to 10HZ.
>

Hmm... and I presume running with preemption disabled doesn't work for 
hotplug (not that this is a hotplug situation)...

2 seconds is a *long* time, but I guess there isn't really nay harm in 
making it 10 seconds in the sense that the system is basically dead at 
that point...

tglx - you have been looking at the CPU startup lately, any opinions?

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.