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

Kirill A. Shutemov
2018-01-10T11:16:43Z

On Wed, Jan 10, 2018 at 03:08:04AM +0000, Dave Young wrote:
> On Tue, Jan 09, 2018 at 12:05:52PM +0300, Kirill A. Shutemov wrote:
> > On Tue, Jan 09, 2018 at 03:24:40PM +0800, Dave Young wrote:
> > > On 01/09/18 at 01:41pm, Baoquan He wrote:
> > > > On 01/09/18 at 09:09am, Dave Young wrote:
> > > >
> > > > > As for the macro name, VMCOREINFO_SYMBOL_ARRAY sounds better.
> >
> > Yep, that's 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.
> >
> > Do you need some action on my side or will you folks take care about this?
>
> I think Baoquan was suggesting to update all array users in current
> code, if you can check every VMCOREINFO_SYMBOL and update all the arrays
> he will be happy. But if can not do it easily I'm fine with a
> VMCOREINFO_SYMBOL_ARRAY changes only now, we kdump people can do it
> later as well.

It seems it's the only array we have there. swapper_pg_dir is a potential
candidate, but it's 'unsigned long' on arm.

Below it patch with corrected macro name.

Please, consider applying.

>From 70f3a84b97f2de98d1364f7b10b7a42a1d8e9968 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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_SYMBOL_ARRAY() that would handle the
situation correctly for both cases.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
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..b511f6d24b42 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_SYMBOL_ARRAY(name) \
+ 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..4f63597c824d 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_SYMBOL_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