Re: [PATCH v6 04/10] crash_core: serialize crash header preparation against hotplug

[Baoquan He]

On 09/02/26 at 03:31pm, Wandun Chen wrote:
> From: Wandun Chen <chenwandun@xxxxxxxxxxx>
> 
> crash_prepare_headers() counts memory ranges before populating the
> allocated crash_mem array. The weak implementation used by ARM64,
> RISC-V and LoongArch walks memblock.memory, while x86 performs the same
> two-pass operation over system RAM resources. Concurrent memory hotplug
> can change range source between the two walks and make the populate
> pass overflow cmem->ranges.
> 
> Take device_hotplug_lock when preparing crash headers during
> kexec_file_load(). The x86 memory hotplug path already takes
> device_hotplug_lock, so call __crash_prepare_headers() directly
> to avoid recursive locking.
> 
> Sashiko reported this issue in [1].
> 
> Fixes: 3751e728cef2 ("arm64: kexec_file: add crash dump support")
> Fixes: 1bcca8620a91 ("LoongArch: Add crash dump support for kexec_file")
> Fixes: 8acea455fafa ("RISC-V: Support for kexec_file on panic")
> Fixes: dd5f726076cc ("kexec: support for kexec on panic using new system call")
> Signed-off-by: Wandun Chen <chenwandun@xxxxxxxxxxx>
> Link: https://sashiko.dev/#/message/20260806101002.1F84E1F000E9@xxxxxxxxxxxxxxx [1]
> ---
>  arch/x86/kernel/crash.c    |  2 +-
>  include/linux/crash_core.h |  2 ++
>  kernel/crash_core.c        | 17 +++++++++++++++--
>  3 files changed, 18 insertions(+), 3 deletions(-)

LGTM,

Acked-by: Baoquan He <baoquan.he@xxxxxxxxx>

> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index e681ec9cf1dc..284d78bc3fd0 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -465,7 +465,7 @@ void arch_crash_handle_hotplug_event(struct kimage *image, void *arg)
>  	 * Create the new elfcorehdr reflecting the changes to CPU and/or
>  	 * memory resources.
>  	 */
> -	if (crash_prepare_headers(IS_ENABLED(CONFIG_X86_64), &elfbuf, &elfsz, NULL)) {
> +	if (__crash_prepare_headers(IS_ENABLED(CONFIG_X86_64), &elfbuf, &elfsz, NULL)) {
>  		pr_err("unable to create new elfcorehdr");
>  		goto out;
>  	}
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index bc087124cd78..28e7a81cf263 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -61,6 +61,8 @@ extern int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_ma
>  				       void **addr, unsigned long *sz);
>  extern int crash_prepare_headers(int need_kernel_map, void **addr,
>  				 unsigned long *sz, unsigned long *nr_mem_ranges);
> +int __crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
> +			    unsigned long *nr_mem_ranges);
>  extern int crash_exclude_core_ranges(struct crash_mem **cmem);
>  
>  struct kimage;
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 77285ae3ce60..3adee1ae120c 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -16,6 +16,7 @@
>  #include <linux/mm.h>
>  #include <linux/cpuhotplug.h>
>  #include <linux/memblock.h>
> +#include <linux/device.h>
>  #include <linux/kmemleak.h>
>  #include <linux/crash_core.h>
>  #include <linux/reboot.h>
> @@ -338,8 +339,8 @@ int crash_exclude_core_ranges(struct crash_mem **cmem)
>  	return 0;
>  }
>  
> -int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
> -			  unsigned long *nr_mem_ranges)
> +int __crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
> +			    unsigned long *nr_mem_ranges)
>  {
>  	unsigned int max_nr_ranges;
>  	struct crash_mem *cmem;
> @@ -376,6 +377,18 @@ int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
>  	return ret;
>  }
>  
> +int crash_prepare_headers(int need_kernel_map, void **addr, unsigned long *sz,
> +			  unsigned long *nr_mem_ranges)
> +{
> +	int ret;
> +
> +	lock_device_hotplug();
> +	ret = __crash_prepare_headers(need_kernel_map, addr, sz, nr_mem_ranges);
> +	unlock_device_hotplug();
> +
> +	return ret;
> +}
> +
>  /**
>   * crash_exclude_mem_range - exclude a mem range for existing ranges
>   * @mem: mem->range contains an array of ranges sorted in ascending order
> -- 
> 2.43.0
>