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

[Jinjie Ruan <ruanjinjie@huawei.com>]

在 2026/10/21 17:48, Wandun 写道:
> 
> 
> 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?

Hi Wandun,

However, I think someone should have informed me in advance; otherwise,
doing duplicate fix work is pointless.

I see that part of your patch series modifies code I previously changed,
but I was not CC'd.

> 
>> 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.

Yes, you are right. If your patch series will be merged soon, I will
develop based on it.

> 
>>
>>> +
>>> +	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
>>
> 

-- 
Best regards,
Jinjie