linux-kernel - [PATCH] kexec: Update vmcoreinfo after crash happened

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Date:   Thu, 16 Mar 2017 20:16:27 +0800
From:   Xunlei Pang <xlpang@...hat.com>
To:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Cc:     akpm@...ux-foundation.org, Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Xunlei Pang <xlpang@...hat.com>
Subject: [PATCH] kexec: Update vmcoreinfo after crash happened

Currently vmcoreinfo data is updated at boot time subsys_initcall(),
it has the risk of being modified by some wrong code during system
is running.

As a result, vmcore dumped will contain the wrong vmcoreinfo. Later on,
when using "crash" utility to parse this vmcore, we probably will get
"Segmentation fault".

Based on the fact that the value of each vmcoreinfo stays invariable
once kernel boots up, we safely move all the vmcoreinfo operations into
crash_save_vmcoreinfo() which is called after crash happened. In this
way, vmcoreinfo data correctness is always guaranteed.

Signed-off-by: Xunlei Pang <xlpang@...hat.com>
---
 kernel/kexec_core.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index bfe62d5..1bfdd96 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1367,12 +1367,6 @@ static void update_vmcoreinfo_note(void)
 	final_note(buf);
 }
 
-void crash_save_vmcoreinfo(void)
-{
-	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
-	update_vmcoreinfo_note();
-}
-
 void vmcoreinfo_append_str(const char *fmt, ...)
 {
 	va_list args;
@@ -1402,7 +1396,7 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void)
 	return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
 }
 
-static int __init crash_save_vmcoreinfo_init(void)
+void crash_save_vmcoreinfo(void)
 {
 	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
 	VMCOREINFO_PAGESIZE(PAGE_SIZE);
@@ -1474,13 +1468,11 @@ static int __init crash_save_vmcoreinfo_init(void)
 #endif
 
 	arch_crash_save_vmcoreinfo();
-	update_vmcoreinfo_note();
+	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
 
-	return 0;
+	update_vmcoreinfo_note();
 }
 
-subsys_initcall(crash_save_vmcoreinfo_init);
-
 /*
  * Move into place and start executing a preloaded standalone
  * executable.  If nothing was preloaded return an error.
-- 
1.8.3.1