linux-kernel - Re: [PATCH] Do not reserve crashkernel high memory if crashkernel low memory reserving failed

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Message-ID: <20151014061637.GA32656@dhcp-128-28.nay.redhat.com>
Date:	Wed, 14 Oct 2015 14:16:37 +0800
From:	Baoquan He <bhe@...hat.com>
To:	akpm@...ux-foundation.org, yinghai@...nel.org, dyoung@...hat.com,
	jroedel@...e.de
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, bp@...e.de,
	linux-kernel@...r.kernel.org, jerry_hoemann@...com
Subject: Re: [PATCH] Do not reserve crashkernel high memory if crashkernel
 low memory reserving failed

Hi all,

Ping.

Any other suggestion for this fix?


On 09/24/15 at 11:24am, Baoquan He wrote:
> People reported that when allocating crashkernel memory using
> ",high" and ",low" syntax, there were cases where the reservation
> of the "high" portion succeeds, but the reservation of the "low"
> portion fails. Then kexec can load kdump kernel successfully, but
> the boot of kdump kernel fails as there's no low memory. This is
> because allocation of low memory for kdump kernel can fail on large
> systems for reasons. E.g it could be manually specified crashkernel
> low memory is too large to find in memblock region.
> 
> In this patch add return value for reserve_crashkernel_low. Then
> try to reserve crashkernel low memory after crashkernel high memory
> has been allocated. If crashkernel low memory reservation failed
> free crashkernel high memory and return. User can take measures
> when they found kdump kernel cann't be loaded successfully.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
> v1->v2:
>   Boris commented that error value EINVAL is negative, should
>   use "return -EINVAL".
> 
> v2->v3:
>   Yinghai pointed out that during memblock_reserve, we could double
>   the memblock reserve array. New memblock reserve could be overlapped
>   with range for crashkernel high. So we have to reserve crashkernel
>   high firstly, then free it if crashkernel low memory allocation
>   failed.
> 
> v3->v4:
>   Dave suggested using "return -ENOMEM" when low memory reservation
>   failed and printing failure message anyway.
> 
> v4->v5:
>   Andrew suggested changing the content of failure message and taking
>   higher severity KERN_ERR.
> 
>  arch/x86/kernel/setup.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index fdb7f2a..e510e61 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -493,7 +493,7 @@ static void __init memblock_x86_reserve_range_setup_data(void)
>  # define CRASH_KERNEL_ADDR_HIGH_MAX	MAXMEM
>  #endif
>  
> -static void __init reserve_crashkernel_low(void)
> +static int __init reserve_crashkernel_low(void)
>  {
>  #ifdef CONFIG_X86_64
>  	const unsigned long long alignment = 16<<20;	/* 16M */
> @@ -522,17 +522,16 @@ static void __init reserve_crashkernel_low(void)
>  	} else {
>  		/* passed with crashkernel=0,low ? */
>  		if (!low_size)
> -			return;
> +			return 0;
>  	}
>  
>  	low_base = memblock_find_in_range(low_size, (1ULL<<32),
>  					low_size, alignment);
>  
>  	if (!low_base) {
> -		if (!auto_set)
> -			pr_info("crashkernel low reservation failed - No suitable area found.\n");
> -
> -		return;
> +		pr_err("Failed to reserve %ldMB of low memory for crashkernel, please try smaller size.\n",
> +				(unsigned long)(low_size >> 20));
> +		return -ENOMEM;
>  	}
>  
>  	memblock_reserve(low_base, low_size);
> @@ -544,6 +543,7 @@ static void __init reserve_crashkernel_low(void)
>  	crashk_low_res.end   = low_base + low_size - 1;
>  	insert_resource(&iomem_resource, &crashk_low_res);
>  #endif
> +	return 0;
>  }
>  
>  static void __init reserve_crashkernel(void)
> @@ -595,6 +595,11 @@ static void __init reserve_crashkernel(void)
>  	}
>  	memblock_reserve(crash_base, crash_size);
>  
> +	if (crash_base >= (1ULL<<32) && reserve_crashkernel_low()) {
> +		memblock_free(crash_base, crash_size);
> +		return;
> +	}
> +
>  	printk(KERN_INFO "Reserving %ldMB of memory at %ldMB "
>  			"for crashkernel (System RAM: %ldMB)\n",
>  			(unsigned long)(crash_size >> 20),
> @@ -604,9 +609,6 @@ static void __init reserve_crashkernel(void)
>  	crashk_res.start = crash_base;
>  	crashk_res.end   = crash_base + crash_size - 1;
>  	insert_resource(&iomem_resource, &crashk_res);
> -
> -	if (crash_base >= (1ULL<<32))
> -		reserve_crashkernel_low();
>  }
>  #else
>  static void __init reserve_crashkernel(void)
> -- 
> 2.4.0
> 
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