+ crash-fix-x86_32-crash-memory-reserve-dead-loop-bug-at-high.patch added to mm-nonmm-unstable branch

+ crash-fix-x86_32-crash-memory-reserve-dead-loop-bug-at-high.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: crash: fix x86_32 crash memory reserve dead loop bug at high
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     crash-fix-x86_32-crash-memory-reserve-dead-loop-bug-at-high.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/crash-fix-x86_32-crash-memory-reserve-dead-loop-bug-at-high.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jinjie Ruan <ruanjinjie@huawei.com>
Subject: crash: fix x86_32 crash memory reserve dead loop bug at high
Date: Thu, 18 Jul 2024 11:54:43 +0800

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.

Link: https://lkml.kernel.org/r/20240718035444.2977105-3-ruanjinjie@huawei.com
Fixes: 9c08a2a139fe ("x86: kdump: use generic interface to simplify crashkernel reservation code")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Baoquan He <bhe@redhat.com>
Tested-by: Jinjie Ruan <ruanjinjie@huawei.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Andrew Davis <afd@ti.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Jiahao <chenjiahao16@huawei.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric DeVolder <eric.devolder@oracle.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/crash_reserve.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/crash_reserve.c~crash-fix-x86_32-crash-memory-reserve-dead-loop-bug-at-high
+++ a/kernel/crash_reserve.c
@@ -413,7 +413,8 @@ retry:
 			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;
 		}
 
 		/*
_

Patches currently in -mm which might be from ruanjinjie@huawei.com are

crash-fix-x86_32-crash-memory-reserve-dead-loop-bug.patch
crash-fix-x86_32-crash-memory-reserve-dead-loop-bug-at-high.patch
arm-use-generic-interface-to-simplify-crashkernel-reservation.patch