linux-kernel - [PATCH] kexec: set prstatus.pr_pid to cpu id when current->pid is 0

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Message-ID: <AANLkTikuUi=i6Lk-ZpE65Gr0tWOeVnrnpWPe85T=J=Ph@mail.gmail.com>
Date:	Tue, 3 Aug 2010 15:21:49 +0800
From:	Hui Zhu <teawater@...il.com>
To:	Eric Biederman <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	WANG Cong <xiyou.wangcong@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Simon Kagstrom <simon.kagstrom@...insight.net>,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kexec: set prstatus.pr_pid to cpu id when current->pid is 0

Hi,

I found that from gdb 7.1 to gdb-cvs-head cannot analyze the core file
that get from kdump.
What I got:
[New <main task>]
[New Thread 2719]
../../src/gdb/thread.c:884: internal-error: switch_to_thread:
Assertion `inf != NULL' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)
That is because:
 objdump -h ./vmcore

./vmcore:     file format elf64-x86-64

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 note0         00000a48  0000000000000000  0000000000000000  00000238  2**0
                  CONTENTS, READONLY
  1 .reg/0        000000d8  0000000000000000  0000000000000000  000002bc  2**2
                  CONTENTS
  2 .reg          000000d8  0000000000000000  0000000000000000  000002bc  2**2
                  CONTENTS
  3 .reg/2719     000000d8  0000000000000000  0000000000000000  00000420  2**2
                  CONTENTS
  4 .reg/0        000000d8  0000000000000000  0000000000000000  00000584  2**2
                  CONTENTS
  5 .reg/0        000000d8  0000000000000000  0000000000000000  000006e8  2**2
                  CONTENTS
Each of reg/n is a cpu core note.  It will be a GDB thread.  n is the
prstatus.pr_pid that will be the thread lwpid.  Because the 3 threads
pid is same, so GDB get error.

current->pid is 0 because this cpu is in idle.  So I add a check, set
prstatus.pr_pid to cpu id when current->pid is 0.  Then GDB work OK
with the core.

Thanks,
Hui

Signed-off-by: Hui Zhu <teawater@...il.com>
---
 kernel/kexec.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1191,7 +1191,10 @@ void crash_save_cpu(struct pt_regs *regs
 	if (!buf)
 		return;
 	memset(&prstatus, 0, sizeof(prstatus));
-	prstatus.pr_pid = current->pid;
+	if (current->pid)
+		prstatus.pr_pid = current->pid;
+	else
+		prstatus.pr_pid = cpu;
 	elf_core_copy_kernel_regs(&prstatus.pr_reg, regs);
 	buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
 		      	      &prstatus, sizeof(prstatus));
--
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