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

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Message-ID: <ZqywtegyIS/YXOVv@MiWiFi-R3L-srv>
Date: Fri, 2 Aug 2024 18:11:01 +0800
From: Baoquan He <bhe@...hat.com>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: 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

On 08/02/24 at 05:01pm, 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
> 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:

Interesting, I didn't expect risc-v defining them like these.

#define CRASH_ADDR_LOW_MAX              dma32_phys_limit
#define CRASH_ADDR_HIGH_MAX             memblock_end_of_DRAM()
> 
> 	-> 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.

And I don't like the idea crashkernel=,high failure will fallback to
attempt in low area, so this looks good to me.

> 
> After this patch, it print:
> 	cannot allocate crashkernel (size:0x1f400000)
> 
> Fixes: 39365395046f ("riscv: kdump: use generic interface to simplify crashkernel reservation")
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>  kernel/crash_reserve.c | 9 ---------
>  1 file changed, 9 deletions(-)

Acked-by: Baoquan He <bhe@...hat.com>

> 
> 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;
> -- 
> 2.34.1
>