linux-kernel - Re: [PATCH v2 3/4] kexec: print out debugging message if required for kexec

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Message-ID: <02A386F1B9701FED+a0b3ab16-3f23-4d69-9fb8-ab4d9f918bad@uniontech.com>
Date: Wed, 5 Nov 2025 16:48:59 +0800
From: Qiang Ma <maqianga@...ontech.com>
To: Baoquan He <bhe@...hat.com>
Cc: akpm@...ux-foundation.org, kexec@...ts.infradead.org,
 linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2 3/4] kexec: print out debugging message if required for
 kexec_load


在 2025/11/5 15:53, Baoquan He 写道:
> On 11/05/25 at 11:41am, Qiang Ma wrote:
>> 在 2025/11/5 11:01, Baoquan He 写道:
>>> On 11/03/25 at 02:34pm, Qiang Ma wrote:
>>>> The commit a85ee18c7900 ("kexec_file: print out debugging message
>>>> if required") has added general code printing in kexec_file_load(),
>>>> but not in kexec_load().
>>>>
>>>> Especially in the RISC-V architecture, kexec_image_info() has been
>>>> removed(commit eb7622d908a0 ("kexec_file, riscv: print out debugging
>>>> message if required")). As a result, when using '-d' for the kexec_load
>>>> interface, print nothing in the kernel space. This might be helpful for
>>>> verifying the accuracy of the data passed to the kernel. Therefore,
>>>> refer to this commit a85ee18c7900 ("kexec_file: print out debugging
>>>> message if required"), debug print information has been added.
>>>>
>>>> Signed-off-by: Qiang Ma <maqianga@...ontech.com>
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>> Closes: https://lore.kernel.org/oe-kbuild-all/202510310332.6XrLe70K-lkp@intel.com/
>>>> ---
>>>>    kernel/kexec.c | 11 +++++++++++
>>>>    1 file changed, 11 insertions(+)
>>>>
>>>> diff --git a/kernel/kexec.c b/kernel/kexec.c
>>>> index c7a869d32f87..9b433b972cc1 100644
>>>> --- a/kernel/kexec.c
>>>> +++ b/kernel/kexec.c
>>>> @@ -154,7 +154,15 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>>>>    	if (ret)
>>>>    		goto out;
>>>> +	kexec_dprintk("nr_segments = %lu\n", nr_segments);
>>>>    	for (i = 0; i < nr_segments; i++) {
>>>> +		struct kexec_segment *ksegment;
>>>> +
>>>> +		ksegment = &image->segment[i];
>>>> +		kexec_dprintk("segment[%lu]: buf=0x%p bufsz=0x%zx mem=0x%lx memsz=0x%zx\n",
>>>> +			      i, ksegment->buf, ksegment->bufsz, ksegment->mem,
>>>> +			      ksegment->memsz);
>>> There has already been a print_segments() in kexec-tools/kexec/kexec.c,
>>> you will get duplicated printing. That sounds not good. Have you tested
>>> this?
>> I have tested it, kexec-tools is the debug message printed
>> in user space, while kexec_dprintk is printed
>> in kernel space.
>>
>> This might be helpful for verifying the accuracy of
>> the data passed to the kernel.
> Hmm, that's not necessary with a debug printing to verify value passed
> in kernel. We should only add debug pringing when we need but lack it.
> I didn't check it carefully, if you add the debug printing only for
> verifying accuracy, that doesn't justify the code change.
>
Also, adding these prints here is helpful for debugging the 
kimage_load_segment().
>>>> +
>>>>    		ret = kimage_load_segment(image, i);
>>>>    		if (ret)
>>>>    			goto out;
>>>> @@ -166,6 +174,9 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>>>>    	if (ret)
>>>>    		goto out;
>>>> +	kexec_dprintk("kexec_load: type:%u, start:0x%lx head:0x%lx flags:0x%lx\n",
>>>> +		      image->type, image->start, image->head, flags);
>>>> +
>>>>    	/* Install the new kernel and uninstall the old */
>>>>    	image = xchg(dest_image, image);
>>>> -- 
>>>> 2.20.1
>>>>
>