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Re: [PATCH] kexec: set prstatus.pr_pid to cpu id when current->pid is 0
- From: Hui Zhu <teawater at gmail dot com>
- To: "Eric W. Biederman" <ebiederm at xmission dot com>
- Cc: Andrew Morton <akpm at linux-foundation dot org>, WANG Cong <xiyou dot wangcong at gmail dot com>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>, Simon Kagstrom <simon dot kagstrom at netinsight dot net>, kexec at lists dot infradead dot org, linux-kernel at vger dot kernel dot org, gdb at sourceware dot org
- Date: Tue, 3 Aug 2010 15:44:35 +0800
- Subject: Re: [PATCH] kexec: set prstatus.pr_pid to cpu id when current->pid is 0
- References: <AANLkTikuUi=i6Lk-ZpE65Gr0tWOeVnrnpWPe85T=J=Ph@mail.gmail.com> <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));
>