Re: [PATCH v9 3/8] crash_core: serialize crash header preparation against hotplug

[Wandun <chenwandun1@gmail.com>]

On 10/21/26 17:13, Jinjie Ruan wrote:
> 
> 
> 在 2026/10/21 16:30, Wandun Chen 写道:
>> From: Wandun Chen <chenwandun@lixiang.com>
>>
>> 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/riscv 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@lixiang.com>
>> Link: https://sashiko.dev/#/message/20260806101002.1F84E1F000E9@smtp.kernel.org [1]
>> Acked-by: Baoquan He <baoquan.he@linux.dev>
>> ---
>>  arch/riscv/kernel/crash.c  |  2 +-
>>  arch/x86/kernel/crash.c    |  2 +-
>>  include/linux/crash_core.h |  2 ++
>>  kernel/crash_core.c        | 17 +++++++++++++++--
>>  4 files changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/crash.c b/arch/riscv/kernel/crash.c
>> index fe5a4b306aae..ac8df2edf2a7 100644
>> --- a/arch/riscv/kernel/crash.c
>> +++ b/arch/riscv/kernel/crash.c
>> @@ -70,7 +70,7 @@ 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(true, &elfbuf, &elfsz, NULL)) {
>> +	if (__crash_prepare_headers(true, &elfbuf, &elfsz, NULL)) {
>>  		pr_err("unable to create new elfcorehdr");
>>  		goto out;
>>  	}
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index e6f23933a6df..bef008a0cb22 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 faa0f22dbb41..8a861a946e26 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>
>> @@ -344,8 +345,8 @@ 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;
>> @@ -382,6 +383,18 @@ 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();
> 
> I think this patch conflicts with my changes and would also conflict
> with the implementation of arm64 crash hotplug.
> 
> https://lore.kernel.org/all/20260921090450.807575-15-ruanjinjie@huawei.com/
> 
Have these patches already been merged? My current work is based on the latest
linux-next. If they have already been merged into the maintainer's branch,
please let me know, I will update my tree and rebase/re-adapt my changes accordingly.


Also, regarding the changes in kernel/crash_core.c: it looks like we modified
the same spot, the change is not wrong, is that right?

> arm64 crash hotplug:
> https://lore.kernel.org/all/20260918100442.3841135-18-ruanjinjie@huawei.com/

In addition, if arm64 gains crash hotplug support, the code there would indeed
need to be modified (to avoid a deadlock). As of now, arm64 crash hotplug
support has not been merged yet either, has it? I just want to make sure I
haven't missed anything.

> 
>> +
>> +	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
>