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@xxxxxxxxxx>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> Tested-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
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
>
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