Re: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y

[Dave Young]

On 01/09/18 at 01:41pm, Baoquan He wrote:
> On 01/09/18 at 09:09am, Dave Young wrote:
> > On 01/09/18 at 03:13am, Kirill A. Shutemov wrote:
> > > On Mon, Jan 08, 2018 at 08:46:53PM +0300, Kirill A. Shutemov wrote:
> > > > On Mon, Jan 08, 2018 at 04:04:44PM +0000, Ingo Molnar wrote:
> > > > > 
> > > > > hi Kirill,
> > > > > 
> > > > > As Mike reported it below, your 5-level paging related upstream commit 
> > > > > 83e3c48729d9 and all its followup fixes:
> > > > > 
> > > > >  83e3c48729d9: mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
> > > > >  629a359bdb0e: mm/sparsemem: Fix ARM64 boot crash when CONFIG_SPARSEMEM_EXTREME=y
> > > > >  d09cfbbfa0f7: mm/sparse.c: wrong allocation for mem_section
> > > > > 
> > > > > ... still breaks kexec - and that now regresses -stable as well.
> > > > > 
> > > > > Given that 5-level paging now syntactically depends on having this commit, if we 
> > > > > fully revert this then we'll have to disable 5-level paging as well.
> > > 
> > > This *should* help.
> > > 
> > > Mike, could you test this? (On top of the rest of the fixes.)
> > > 
> > > Sorry for the mess.
> > > 
> > > From 100fd567754f1457be94732046aefca204c842d2 Mon Sep 17 00:00:00 2001
> > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > Date: Tue, 9 Jan 2018 02:55:47 +0300
> > > Subject: [PATCH] kdump: Write a correct address of mem_section into vmcoreinfo
> > > 
> > > Depending on configuration mem_section can now be an array or a pointer
> > > to an array allocated dynamically. In most cases, we can continue to refer
> > > to it as 'mem_section' regardless of what it is.
> > > 
> > > But there's one exception: '&mem_section' means "address of the array" if
> > > mem_section is an array, but if mem_section is a pointer, it would mean
> > > "address of the pointer".
> > > 
> > > We've stepped onto this in kdump code. VMCOREINFO_SYMBOL(mem_section)
> > > writes down address of pointer into vmcoreinfo, not array as we wanted.
> > > 
> > > Let's introduce VMCOREINFO_ARRAY() that would handle the situation
> > > correctly for both cases.
> > > 
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
> > > ---
> > >  include/linux/crash_core.h | 2 ++
> > >  kernel/crash_core.c        | 2 +-
> > >  2 files changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> > > index 06097ef30449..83ae04950269 100644
> > > --- a/include/linux/crash_core.h
> > > +++ b/include/linux/crash_core.h
> > > @@ -42,6 +42,8 @@ phys_addr_t paddr_vmcoreinfo_note(void);
> > >  	vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
> > >  #define VMCOREINFO_SYMBOL(name) \
> > >  	vmcoreinfo_append_str("SYMBOL(%s)=%lx\n", #name, (unsigned long)&name)
> > > +#define VMCOREINFO_ARRAY(name) \
> > 
> > Thanks for the patch, I have a similar patch but makedumpfile maintainer
> > is looking at a userspace fix instead.
> 
> Seems we should add lkml to CC next time so that people can watch it.

Yes, agreed.

> 
> > As for the macro name, VMCOREINFO_SYMBOL_ARRAY sounds better.
> 
> I still think using vmcoreinfo_append_str is better. Unless we replace
> all array variables with the newly added macro.
> 
> vmcoreinfo_append_str("SYMBOL(mem_section)=%lx\n",
>                                 (unsigned long)mem_section);

I have no strong opinion, either change all array uses or just introduce
the macro and start to use it from now on if we have similar array
symbols.

> > 
> > > +	vmcoreinfo_append_str("SYMBOL(%s)=%lx\n", #name, (unsigned long)name)
> > >  #define VMCOREINFO_SIZE(name) \
> > >  	vmcoreinfo_append_str("SIZE(%s)=%lu\n", #name, \
> > >  			      (unsigned long)sizeof(name))
> > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> > > index b3663896278e..d4122a837477 100644
> > > --- a/kernel/crash_core.c
> > > +++ b/kernel/crash_core.c
> > > @@ -410,7 +410,7 @@ static int __init crash_save_vmcoreinfo_init(void)
> > >  	VMCOREINFO_SYMBOL(contig_page_data);
> > >  #endif
> > >  #ifdef CONFIG_SPARSEMEM
> > > -	VMCOREINFO_SYMBOL(mem_section);
> > > +	VMCOREINFO_ARRAY(mem_section);
> > >  	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
> > >  	VMCOREINFO_STRUCT_SIZE(mem_section);
> > >  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> > > -- 
> > >  Kirill A. Shutemov
> > 
> > Thanks
> > Dave

Thanks
Dave