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

[Qiang Ma]

On 2025/11/5 下午9:01, Baoquan He wrote:
> On 11/05/25 at 07:28pm, Qiang Ma wrote:
> > 在 2025/11/5 16:55, Baoquan He 写道:
> > > On 11/05/25 at 04:35pm, Qiang Ma wrote:
> > > > 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@xxxxxxxxxxxxx>
> > > > > > > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > > > > > > Closes: https://lore.kernel.org/oe-kbuild-all/202510310332.6XrLe70K-lkp@xxxxxxxxx/
> > > > > > > > ---
> > > > > > > >      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.
> > > > It's not entirely because of it.
> > > >
> > > > Another reason is that for RISC-V, for kexec_file_load interface,
> > > > kexec_image_info() was deleted at that time because the content
> > > > has been printed out in generic code.
> > > >
> > > > However, these contents were not printed in kexec_load because
> > > > kexec_image_info was deleted. So now it has been added.
> > > print_segments() in kexec-tools/kexec/kexec.c is a generic function,
> > > shouldn't you make it called in kexec-tools for risc-v? I am confused by
> > > the purpose of this patchset.
> > There is a problem with what I expressed.
> > I don't want to add print_segments to riscv.
> > I want to add some debugging message(ksegment,kimage,flag) for kexec_load.
> >
> > Although ksegment debugging message has been printed in kexec-tools,
> > it is still helpful for debugging the kernel space function.
> Sorry, I can't support that. We all prepare the loading segments for the
> future jumping in kexec_tools if it's kexec_load interface. And calling
> print_segments() to print those loading information is natural. Why do we
> need print them two times for verifying if the printing is accuracy?
Is it necessary to verify the user-space data after it is passed to the 
kernel space?

> Could you explain why risc-v is special?
At first, when I saw that in the RISC-V architecture,
after kexec_image_info was removed from this commit eb7622d908a0
("kexec_file, riscv: print out debugging message if required"),
I thought only kexec_file_load was taken into consideration.
However, without considering that kexec_load would call
kexec_image_info to print segment and other debugging message,
I think that since it has been deleted.

Then, I referred to kexec_file_load and added these debugging message
to the general code of kexec_load. In this way, all architectures can
print these general debugging message.

Then I can add these debugging message to the general code,
so that all architectures can print these general debugging message.
> > > > > > > > +
> > > > > > > >      		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