Re: [PATCH v4 08/10] crash hp: exclude hot remove cpu from elfcorehdr notes

[Eric DeVolder]

On 2/22/22 22:04, Baoquan He wrote:
> On 02/09/22 at 02:57pm, Eric DeVolder wrote:
> > Due to use of CPUHP_AP_ONLINE_DYN, upon CPU unplug, the CPU is
> > still in the for_each_present_cpu() list when within the
> > crash_hotplug_handler(). Thus the CPU must be explicitly excluded
> > when building the new list of CPUs.
> >
> > This change identifies in crash_hotplug_handler() the CPU to be
> > excluded, and the check for excluding the CPU in
> > crash_prepare_elf64_headers().
>
> This looks good to me, and the particularity of cpu hotplug can be
> understood well by other code reader. Thanks.
>
> Acked-by: Baoquan He <bhe@xxxxxxxxxx>
Thank you!
eric
> > Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
> > ---
> >   kernel/crash_core.c | 10 ++++++++++
> >   kernel/kexec_file.c |  5 +++++
> >   2 files changed, 15 insertions(+)
> >
> > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > index 524470e18883..b6942e04a188 100644
> > --- a/kernel/crash_core.c
> > +++ b/kernel/crash_core.c
> > @@ -550,6 +550,16 @@ static void crash_hotplug_handler(unsigned int hp_action,
> >   		/* Flag to differentiate between normal load and hotplug */
> >   		kexec_crash_image->hotplug_event = true;
> >   
> > +		/*
> > +		 * Due to use of CPUHP_AP_ONLINE_DYN, upon unplug and during
> > +		 * this callback, the CPU is still in the for_each_present_cpu()
> > +		 * list. Must explicitly look to exclude this CPU when building
> > +		 * new list.
> > +		 */
> > +		kexec_crash_image->offlinecpu =
> > +			(hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
> > +				(unsigned int)a : ~0U;
> > +
> >   		/* Now invoke arch-specific update handler */
> >   		arch_crash_hotplug_handler(kexec_crash_image, hp_action, a, b);
> >   
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index 93bb0c0ce66c..339995d42169 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -1314,6 +1314,11 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
> >   
> >   	/* Prepare one phdr of type PT_NOTE for each present CPU */
> >   	for_each_present_cpu(cpu) {
> > +#ifdef CONFIG_CRASH_HOTPLUG
> > +		/* Skip the soon-to-be offlined cpu */
> > +		if (image->hotplug_event && (cpu == image->offlinecpu))
> > +			continue;
> > +#endif
> >   		phdr->p_type = PT_NOTE;
> >   		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
> >   		phdr->p_offset = phdr->p_paddr = notes_addr;
> > --
> > 2.27.0