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

Alexandre Ghiti
2024-08-02T12:24:23Z

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@huawei.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;