linux-kernel - Re: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM

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Message-ID: <20180109001303.dy73bpixsaegn4ol@node.shutemov.name>
Date:   Tue, 9 Jan 2018 03:13:03 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...e.de>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, kexec@...ts.infradead.org
Subject: Re: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at
 runtime for CONFIG_SPARSEMEM_EXTREME=y

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@...ux.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_ARRAY() that would handle the situation
correctly for both cases.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.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..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) \
+	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