linux-kernel - [PATCH v3 2/3] crash: Fix x86_32 crash memory reserve dead loop bug at high

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Message-ID: <20240718035444.2977105-3-ruanjinjie@huawei.com>
Date: Thu, 18 Jul 2024 11:54:43 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: <linux@...linux.org.uk>, <catalin.marinas@....com>, <will@...nel.org>,
	<paul.walmsley@...ive.com>, <palmer@...belt.com>, <aou@...s.berkeley.edu>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <hpa@...or.com>, <bhe@...hat.com>,
	<vgoyal@...hat.com>, <dyoung@...hat.com>, <arnd@...db.de>, <afd@...com>,
	<linus.walleij@...aro.org>, <akpm@...ux-foundation.org>,
	<eric.devolder@...cle.com>, <gregkh@...uxfoundation.org>,
	<javierm@...hat.com>, <deller@....de>, <robh@...nel.org>,
	<hbathini@...ux.ibm.com>, <thunder.leizhen@...wei.com>,
	<chenjiahao16@...wei.com>, <linux-kernel@...r.kernel.org>,
	<kexec@...ts.infradead.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-riscv@...ts.infradead.org>
CC: <ruanjinjie@...wei.com>
Subject: [PATCH v3 2/3] crash: Fix x86_32 crash memory reserve dead loop bug at high

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@...wei.com>
Signed-off-by: Baoquan He <bhe@...hat.com>
Tested-by: Jinjie Ruan <ruanjinjie@...wei.com>
---
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