linux-kernel - [PATCH v2] crash: Fix x86_32 memory reserve dead loop retry bug

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Message-ID: <20240711073118.1289866-1-ruanjinjie@huawei.com>
Date: Thu, 11 Jul 2024 15:31:18 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: <bhe@...hat.com>, <vgoyal@...hat.com>, <dyoung@...hat.com>,
	<akpm@...ux-foundation.org>, <kexec@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2] crash: Fix x86_32 memory reserve dead loop retry bug

On x86_32 Qemu machine with 1GB memory, the cmdline "crashkernel=1G,high"
will 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 high crash kernel memory reservation will fail, then
go into the "retry" loop and never came out as below.

-> 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).

Fix it by change the out check condition.

After this patch, it print:
	cannot allocate crashkernel (size:0x40000000)

Fixes: 9c08a2a139fe ("x86: kdump: use generic interface to simplify crashkernel reservation code")
Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
---
v2:
- Peel off the other two patches.
- Update the commit message and fix tag.
---
 kernel/crash_reserve.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
index 5b2722a93a48..5073ae205f79 100644
--- a/kernel/crash_reserve.c
+++ b/kernel/crash_reserve.c
@@ -421,7 +421,7 @@ void __init reserve_crashkernel_generic(char *cmdline,
 		 * 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) {
+		if (high && search_base == CRASH_ADDR_LOW_MAX) {
 			search_end = CRASH_ADDR_LOW_MAX;
 			search_base = 0;
 			goto retry;
-- 
2.34.1