[PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Pingfan Liu]

As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
formula:
    #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)

Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
PAGES_PER_SECTION in makedumpfile just like kernel.

Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
SECTION_SIZE_BITS"). But user space wants a stable interface to get this
info. Such info is impossible to be deduced from a crashdump vmcore.
Hence append SECTION_SIZE_BITS to vmcoreinfo.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Boris Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: James Morse <james.morse@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Anderson <anderson@redhat.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org
Cc: x86@kernel.org
Cc: linux-arm-kernel@lists.infradead.org
---
 kernel/crash_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 825284baaf46..684a6061a13a 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -464,6 +464,7 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
 	VMCOREINFO_STRUCT_SIZE(mem_section);
 	VMCOREINFO_OFFSET(mem_section, section_mem_map);
+	VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
 	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
 #endif
 	VMCOREINFO_STRUCT_SIZE(page);
-- 
2.29.2

Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Baoquan He]

On 06/08/21 at 06:33am, Pingfan Liu wrote:
> As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
> Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
> formula:
>     #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
> 
> Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
> PAGES_PER_SECTION in makedumpfile just like kernel.
> 
> Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
> recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
> SECTION_SIZE_BITS"). But user space wants a stable interface to get this
> info. Such info is impossible to be deduced from a crashdump vmcore.
> Hence append SECTION_SIZE_BITS to vmcoreinfo.

> 
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Bhupesh Sharma <bhupesh.sharma@linaro.org>
> Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Boris Petkov <bp@alien8.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: James Morse <james.morse@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Dave Anderson <anderson@redhat.com>
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kexec@lists.infradead.org
> Cc: x86@kernel.org
> Cc: linux-arm-kernel@lists.infradead.org


Add the discussion of the original thread in kexec ML for reference:
http://lists.infradead.org/pipermail/kexec/2021-June/022676.html

This looks good to me.

Acked-by: Baoquan He <bhe@redhat.com>

> ---
>  kernel/crash_core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 825284baaf46..684a6061a13a 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -464,6 +464,7 @@ static int __init crash_save_vmcoreinfo_init(void)
>  	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
>  	VMCOREINFO_STRUCT_SIZE(mem_section);
>  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> +	VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
>  	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>  #endif
>  	VMCOREINFO_STRUCT_SIZE(page);
> -- 
> 2.29.2
> 

Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Andrew Morton]

On Tue, 8 Jun 2021 22:24:32 +0800 Baoquan He <bhe@redhat.com> wrote:

> On 06/08/21 at 06:33am, Pingfan Liu wrote:
> > As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
> > Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
> > formula:
> >     #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
> > 
> > Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
> > PAGES_PER_SECTION in makedumpfile just like kernel.
> > 
> > Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
> > recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
> > SECTION_SIZE_BITS"). But user space wants a stable interface to get this
> > info. Such info is impossible to be deduced from a crashdump vmcore.
> > Hence append SECTION_SIZE_BITS to vmcoreinfo.
> 
> ...
>
> Add the discussion of the original thread in kexec ML for reference:
> http://lists.infradead.org/pipermail/kexec/2021-June/022676.html

I added a Link: for this.
 
> This looks good to me.
> 
> Acked-by: Baoquan He <bhe@redhat.com>

I'm thinking we should backport this at least to Fixes:f0b13ee23241. 
But perhaps it's simpler to just backport it as far as possible, so I
added a bare cc:stable with no Fixes:.  Thoughts?

Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Pingfan Liu]

Correct mail address of Kazuhito

On Tue, Jun 8, 2021 at 6:34 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
> Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
> formula:
>     #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
>
> Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
> PAGES_PER_SECTION in makedumpfile just like kernel.
>
> Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
> recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
> SECTION_SIZE_BITS"). But user space wants a stable interface to get this
> info. Such info is impossible to be deduced from a crashdump vmcore.
> Hence append SECTION_SIZE_BITS to vmcoreinfo.
>
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Bhupesh Sharma <bhupesh.sharma@linaro.org>
> Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Boris Petkov <bp@alien8.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: James Morse <james.morse@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Dave Anderson <anderson@redhat.com>
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kexec@lists.infradead.org
> Cc: x86@kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> ---
>  kernel/crash_core.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 825284baaf46..684a6061a13a 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -464,6 +464,7 @@ static int __init crash_save_vmcoreinfo_init(void)
>         VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
>         VMCOREINFO_STRUCT_SIZE(mem_section);
>         VMCOREINFO_OFFSET(mem_section, section_mem_map);
> +       VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
>         VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>  #endif
>         VMCOREINFO_STRUCT_SIZE(page);
> --
> 2.29.2
>

Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Baoquan He]

On 06/08/21 at 02:14pm, Andrew Morton wrote:
> On Tue, 8 Jun 2021 22:24:32 +0800 Baoquan He <bhe@redhat.com> wrote:
> 
> > On 06/08/21 at 06:33am, Pingfan Liu wrote:
> > > As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
> > > Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
> > > formula:
> > >     #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
> > > 
> > > Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
> > > PAGES_PER_SECTION in makedumpfile just like kernel.
> > > 
> > > Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
> > > recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
> > > SECTION_SIZE_BITS"). But user space wants a stable interface to get this
> > > info. Such info is impossible to be deduced from a crashdump vmcore.
> > > Hence append SECTION_SIZE_BITS to vmcoreinfo.
> > 
> > ...
> >
> > Add the discussion of the original thread in kexec ML for reference:
> > http://lists.infradead.org/pipermail/kexec/2021-June/022676.html
> 
> I added a Link: for this.

Thanks, Andrew.

>  
> > This looks good to me.
> > 
> > Acked-by: Baoquan He <bhe@redhat.com>
> 
> I'm thinking we should backport this at least to Fixes:f0b13ee23241. 
> But perhaps it's simpler to just backport it as far as possible, so I
> added a bare cc:stable with no Fixes:.  Thoughts?

Yeah, it should add cc:stable, thanks. Otherwise it will break
vmcore dumping on 5.12 stable kernel even though with the updated
makedumpfile utility. Fixes:f0b13ee23241 will help stable kernel
maintainer easier to identify which kernel this patch need be applied
on? If only having cc:stable with no Fixes is allowed, it's also OK.