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...

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