linux-kernel - Re: [PATCH v3 2/3] crash: Fix x86_32 crash memory reserve dead loop bug at high

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Message-ID: <Zpj4+G5OwTYBQGIA@MiWiFi-R3L-srv>
Date: Thu, 18 Jul 2024 19:14:00 +0800
From: Baoquan He <bhe@...hat.com>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, hpa@...or.com, vgoyal@...hat.com,
	dyoung@...hat.com, arnd@...db.de, afd@...com,
	linus.walleij@...aro.org, akpm@...ux-foundation.org,
	eric.devolder@...cle.com, gregkh@...uxfoundation.org,
	javierm@...hat.com, deller@....de, robh@...nel.org,
	hbathini@...ux.ibm.com, thunder.leizhen@...wei.com,
	chenjiahao16@...wei.com, linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3 2/3] crash: Fix x86_32 crash memory reserve dead loop
 bug at high

On 07/18/24 at 11:54am, Jinjie Ruan wrote:

I don't fully catch the subject, what does the 'dead loop bug at high'
mean?

> On x86_32 Qemu machine with 1GB memory, the cmdline "crashkernel=512M" will
> also cause system stall as below:
> 
> 	ACPI: Reserving FACP table memory at [mem 0x3ffe18b8-0x3ffe192b]
> 	ACPI: Reserving DSDT table memory at [mem 0x3ffe0040-0x3ffe18b7]
> 	ACPI: Reserving FACS table memory at [mem 0x3ffe0000-0x3ffe003f]
> 	ACPI: Reserving APIC table memory at [mem 0x3ffe192c-0x3ffe19bb]
> 	ACPI: Reserving HPET table memory at [mem 0x3ffe19bc-0x3ffe19f3]
> 	ACPI: Reserving WAET table memory at [mem 0x3ffe19f4-0x3ffe1a1b]
> 	143MB HIGHMEM available.
> 	879MB LOWMEM available.
> 	  mapped low ram: 0 - 36ffe000
> 	  low ram: 0 - 36ffe000
> 	  (stall here)
> 
> The reason is that the CRASH_ADDR_LOW_MAX is equal to CRASH_ADDR_HIGH_MAX
> on x86_32, the first "low" crash kernel memory reservation for 512M fails,
> then it go into the "retry" loop and never came out as below (consider
> CRASH_ADDR_LOW_MAX = CRASH_ADDR_HIGH_MAX = 512M):
> 
> -> reserve_crashkernel_generic() and high is false
>    -> alloc at [0, 0x20000000] fail
>       -> alloc at [0x20000000, 0x20000000] fail and repeatedly
>       (because CRASH_ADDR_LOW_MAX = CRASH_ADDR_HIGH_MAX).
> 
> Fix it by skipping meaningless calls of memblock_phys_alloc_range() with
> `start = end`
> 
> After this patch, the retry dead loop is avoided and print below info:
> 	cannot allocate crashkernel (size:0x20000000)
> 
> And apply generic crashkernel reservation to 32bit system will be ready.
> 
> Fixes: 9c08a2a139fe ("x86: kdump: use generic interface to simplify crashkernel reservation code")
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> Signed-off-by: Baoquan He <bhe@...hat.com>
> Tested-by: Jinjie Ruan <ruanjinjie@...wei.com>

Also the tag issues, please update.

Other than above concerns, the patch looks good to me.

> ---
> v3:
> - Fix it as Baoquan suggested.
> - Update the commit message.
> ---
>  kernel/crash_reserve.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index c5213f123e19..dacc268429e2 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -414,7 +414,8 @@ void __init reserve_crashkernel_generic(char *cmdline,
>  			search_end = CRASH_ADDR_HIGH_MAX;
>  			search_base = CRASH_ADDR_LOW_MAX;
>  			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> -			goto retry;
> +			if (search_base != search_end)
> +				goto retry;
>  		}
>  
>  		/*
> -- 
> 2.34.1
>