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

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Date:	Wed, 08 Aug 2012 00:33:49 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	"Chen, LinX Z" <linx.z.chen@...el.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	hpa@...or.com, yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH] x86/smp: Fix cpuN startup panic

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?
	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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