linux-kernel - Re: [PATCH -next v2] crash: Fix riscv64 crash memory reserve dead loop

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Message-ID: <ZrrTpgvC/buAY/OV@MiWiFi-R3L-srv>
Date: Tue, 13 Aug 2024 11:31:50 +0800
From: Baoquan He <bhe@...hat.com>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: catalin.marinas@....com, vgoyal@...hat.com, dyoung@...hat.com,
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org, linux-riscv@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH -next v2] crash: Fix riscv64 crash memory reserve dead
 loop

On 08/12/24 at 02:20pm, 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:
> 
> 	-> 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).
> 
> As Catalin suggested, do not remove the ",high" reservation fallback to
> ",low" logic which will change arm64's kdump behavior, but fix it by
> skipping the above situation similar to commit d2f32f23190b ("crash: fix
> x86_32 crash memory reserve dead loop").
> 
> After this patch, it print:
> 	cannot allocate crashkernel (size:0x1f400000)
> 
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> Suggested-by: Catalin Marinas <catalin.marinas@....com>
> ---
> v2:
> - Fix it in another way suggested by Catalin.
> - Add Suggested-by.
> ---
>  kernel/crash_reserve.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

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

> 
> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
> index 5387269114f6..aae4a9e998d1 100644
> --- a/kernel/crash_reserve.c
> +++ b/kernel/crash_reserve.c
> @@ -427,7 +427,8 @@ void __init reserve_crashkernel_generic(char *cmdline,
>  		if (high && search_end == CRASH_ADDR_HIGH_MAX) {
>  			search_end = CRASH_ADDR_LOW_MAX;
>  			search_base = 0;
> -			goto retry;
> +			if (search_end != CRASH_ADDR_HIGH_MAX)
> +				goto retry;
>  		}
>  		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>  			crash_size);
> -- 
> 2.34.1
>