From: Hui Zhu <teawater@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
WANG Cong <xiyou.wangcong@gmail.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Simon Kagstrom <simon.kagstrom@netinsight.net>,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
gdb@sourceware.org
Subject: Re: [PATCH] kexec: set prstatus.pr_pid to cpu id when current->pid is 0
Date: Tue, 03 Aug 2010 07:45:00 -0000 [thread overview]
Message-ID: <AANLkTi=-By6ZWjo9bW0s4MndFftHegROO7oa0jbpnCho@mail.gmail.com> (raw)
In-Reply-To: <m1zkx4w3hx.fsf@fess.ebiederm.org>
On Tue, Aug 3, 2010 at 15:37, Eric W. Biederman <ebiederm@xmission.com> wrote:
> Hui Zhu <teawater@gmail.com> writes:
>
>> 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.
>
> That is a gdb limitation. It looks to me like applying this patch will
> loose information, and give you no guarantee that prstatus.pr_pid will
> not equal 0.
>
> If you want to change something please do it in a post processing tool.
>
> Eric
Equal 0 is not a bug, the trouble is a lot of core's pid is same.
This is what gdb say:
/* Found an old thread with the same id. It has to be dead,
otherwise we wouldn't be adding a new thread with the same id.
The OS is reusing this id --- delete it, and recreate a new
one. */
Hui
>
>
>> Thanks,
>> Hui
>>
>> Signed-off-by: Hui Zhu <teawater@gmail.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));
>
next parent reply other threads:[~2010-08-03 7:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AANLkTikuUi=i6Lk-ZpE65Gr0tWOeVnrnpWPe85T=J=Ph@mail.gmail.com>
[not found] ` <m1zkx4w3hx.fsf@fess.ebiederm.org>
2010-08-03 7:45 ` Hui Zhu [this message]
2010-08-03 8:15 ` Eric W. Biederman
2010-08-03 8:37 ` Simon Horman
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