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

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Message-ID: <aQsCaeTx0WduSjSz@MiWiFi-R3L-srv>
Date: Wed, 5 Nov 2025 15:53:13 +0800
From: Baoquan He <bhe@...hat.com>
To: Qiang Ma <maqianga@...ontech.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

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.

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