linux-kernel - Re: [PATCH -next] crash: Fix riscv64 crash memory reserve dead loop

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Message-ID: <ce86ad6b-5f56-4856-9756-fa8867d0d1df@ghiti.fr>
Date: Fri, 2 Aug 2024 14:24:19 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Jinjie Ruan <ruanjinjie@...wei.com>, bhe@...hat.com, vgoyal@...hat.com,
 dyoung@...hat.com, paul.walmsley@...ive.com, palmer@...belt.com,
 aou@...s.berkeley.edu, chenjiahao16@...wei.com, akpm@...ux-foundation.org,
 kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org
Subject: Re: [PATCH -next] crash: Fix riscv64 crash memory reserve dead loop

Hi Jinjie,

On 02/08/2024 11:01, Jinjie Ruan wrote:
> On RISCV64 Qemu machine with 512MB memory, cmdline "crashkernel=500M,high"
> will cause system stall as below:
>
> 	 Zone ranges:
> 	   DMA32    [mem 0x0000000080000000-0x000000009fffffff]
> 	   Normal   empty
> 	 Movable zone start for each node
> 	 Early memory node ranges
> 	   node   0: [mem 0x0000000080000000-0x000000008005ffff]
> 	   node   0: [mem 0x0000000080060000-0x000000009fffffff]
> 	 Initmem setup node 0 [mem 0x0000000080000000-0x000000009fffffff]
> 	(stall here)
>
> commit 5d99cadf1568 ("crash: fix x86_32 crash memory reserve dead loop


I can't find this revision, was this patch merged in 6.11?


> bug") fix this on 32-bit architecture. However, the problem is not
> completely solved. If `CRASH_ADDR_LOW_MAX = CRASH_ADDR_HIGH_MAX` on 64-bit
> architecture, for example, when system memory is equal to
> CRASH_ADDR_LOW_MAX on RISCV64, the following infinite loop will also occur:
>
> 	-> reserve_crashkernel_generic() and high is true
> 	   -> alloc at [CRASH_ADDR_LOW_MAX, CRASH_ADDR_HIGH_MAX] fail
> 	      -> alloc at [0, CRASH_ADDR_LOW_MAX] fail and repeatedly
> 	         (because CRASH_ADDR_LOW_MAX = CRASH_ADDR_HIGH_MAX).
>
> Before refactor in commit 9c08a2a139fe ("x86: kdump: use generic interface
> to simplify crashkernel reservation code"), x86 do not try to reserve crash
> memory at low if it fails to alloc above high 4G. However before refator in
> commit fdc268232dbba ("arm64: kdump: use generic interface to simplify
> crashkernel reservation"), arm64 try to reserve crash memory at low if it
> fails above high 4G. For 64-bit systems, this attempt is less beneficial
> than the opposite, remove it to fix this bug and align with native x86
> implementation.
>
> After this patch, it print:
> 	cannot allocate crashkernel (size:0x1f400000)
>
> Fixes: 39365395046f ("riscv: kdump: use generic interface to simplify crashkernel reservation")


Your patch subject indicates "-next" but I see this commit ^ landed in 
6.7, so I think we should merge it now, let me know if I missed something.

Thanks,

Alex


> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>   kernel/crash_reserve.c | 9 ---------
>   1 file changed, 9 deletions(-)
>
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index 5387269114f6..69e4b8b7b969 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -420,15 +420,6 @@ void __init reserve_crashkernel_generic(char *cmdline,
>   				goto retry;
>   		}
>   
> -		/*
> -		 * For crashkernel=size[KMG],high, if the first attempt was
> -		 * for high memory, fall back to low memory.
> -		 */
> -		if (high && search_end == CRASH_ADDR_HIGH_MAX) {
> -			search_end = CRASH_ADDR_LOW_MAX;
> -			search_base = 0;
> -			goto retry;
> -		}
>   		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>   			crash_size);
>   		return;