linux-kernel - Re: [PATCH] kdump: Fix gdb macros work work with newer and 64-bit kernels

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Date:	Mon, 9 May 2016 07:10:59 -0500
From:	Corey Minyard <minyard@....org>
To:	Baoquan He <bhe@...hat.com>
Cc:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Vivek Goyal <vgoyal@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	Corey Minyard <cminyard@...sta.com>, dyoung@...hat.com
Subject: Re: [PATCH] kdump: Fix gdb macros work work with newer and 64-bit
 kernels

On 05/09/2016 12:18 AM, Baoquan He wrote:
> Hi Corey,
>
> I am trying to review this patch now, and these fixes contained are very
> great. Just several concerns are added in inline comment.
>
> By the way, did you run this in your side?

Yes, I tested on x86, x86_64, ARM and MIPS.

Comments inline...


> Hi Vivek,
>
> Member variable was added into task_struct in below commit replacing
> pids[PIDTYPE_TGID], and from then on nobody complained about it. Seems
> people rarely use this utility.
>
> commit 47e65328a7b1cdfc4e3102e50d60faf94ebba7d3
> Author: Oleg Nesterov <oleg@...sign.ru>
> Date:   Tue Mar 28 16:11:25 2006 -0800
>
>      [PATCH] pids: kill PIDTYPE_TGID
>
>
>
> On 04/27/16 at 07:21am, Corey Minyard wrote:
>> Any comments on this?  If no one else cares I'd be willing to take over
>> maintenance of this.
>>
>> -corey
>>
>> On 02/25/2016 07:51 AM, minyard@....org wrote:
>>> From: Corey Minyard <cminyard@...sta.com>
>>>
>>> Lots of little changes needed to be made to clean these up, remove the
>>> four byte pointer assumption and traverse the pid queue properly.
>>> Also consolidate the traceback code into a single function instead
>>> of having three copies of it.
>>>
>>> Signed-off-by: Corey Minyard <cminyard@...sta.com>
>>> ---
>>>   Documentation/kdump/gdbmacros.txt | 90 +++++++++++++++++----------------------
>>>   1 file changed, 40 insertions(+), 50 deletions(-)
>>>
>>> I sent this earlier, but I didn't get a response.  These are clearly
>>> wrong.  I'd be happy to take over maintenance of these macros.  It
>>> might be better to move them someplace else, too, since they are also
>>> useful for kgdb.
>>>
>>> diff --git a/Documentation/kdump/gdbmacros.txt b/Documentation/kdump/gdbmacros.txt
>>> index 9b9b454..e5bbd8d 100644
>>> --- a/Documentation/kdump/gdbmacros.txt
>>> +++ b/Documentation/kdump/gdbmacros.txt
>>> @@ -15,14 +15,14 @@
>>>   define bttnobp
>>>   	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
>>> -	set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
>>> +	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
> This is a quite nice fix.
>
>>>   	set $init_t=&init_task
>>>   	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
>>>   	while ($next_t != $init_t)
>>>   		set $next_t=(struct task_struct *)$next_t
>>>   		printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
>>>   		printf "===================\n"
>>> -		set var $stackp = $next_t.thread.esp
>>> +		set var $stackp = $next_t.thread.sp
>>>   		set var $stack_top = ($stackp & ~4095) + 4096
>>>   		while ($stackp < $stack_top)
>>> @@ -31,12 +31,12 @@ define bttnobp
>>>   			end
>>>   			set $stackp += 4
>>>   		end
>>> -		set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
>>> +		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
>>>   		while ($next_th != $next_t)
>>>   			set $next_th=(struct task_struct *)$next_th
>>>   			printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
>>>   			printf "===================\n"
>>> -			set var $stackp = $next_t.thread.esp
>>> +			set var $stackp = $next_t.thread.sp
>>>   			set var $stack_top = ($stackp & ~4095) + 4096
>>>   			while ($stackp < $stack_top)
>>> @@ -45,7 +45,7 @@ define bttnobp
>>>   				end
>>>   				set $stackp += 4
>>>   			end
>>> -			set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
>>> +			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
>>>   		end
>>>   		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
>>>   	end
>>> @@ -54,42 +54,43 @@ document bttnobp
>>>   	dump all thread stack traces on a kernel compiled with !CONFIG_FRAME_POINTER
>>>   end
>>> +define btthreadstruct
> This is a nice wrapping, but I guess you want to name it as
> btthreadstack, right? Since I didn't get at all why it's related to
> thread_struct except of getting 'sp'.
>

The name is based on what is passed into the function.  You do a 
backtrace when given a thread structure.  In my experience it is best to 
name functions based upon how the function's user sees it. Though I'm 
not stuck on the name, if you would prefer btthreadstack.

>>> +	set var $pid_task = $arg0
>>> +
>>> +	printf "\npid %d; comm %s:\n", $pid_task.pid, $pid_task.comm
>>> +	printf "task struct: "
>>> +	print $pid_task
>>> +	printf "===================\n"
>>> +	set var $stackp = $pid_task.thread.sp
>>> +	set var $stack_top = ($stackp & ~4095) + 4096
>>> +	set var $stack_bot = ($stackp & ~4095)
>>> +
>>> +	set $stackp = *((unsigned long *) $stackp)
>>> +	while (($stackp < $stack_top) && ($stackp > $stack_bot))
>>> +		set var $addr = *(((unsigned long *) $stackp) + 1)
>>> +		info symbol $addr
>>> +		set $stackp = *((unsigned long *) $stackp)
>>> +	end
>>> +end
>>> +document btthreadstruct
>>> +	 dump a thread stack using the given task structure pointer
>>> +end
>>> +
>>> +
>>>   define btt
>>>   	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
>>> -	set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
>>> +	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
>>>   	set $init_t=&init_task
>>>   	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
>>>   	while ($next_t != $init_t)
>>>   		set $next_t=(struct task_struct *)$next_t
>>> -		printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
>>> -		printf "===================\n"
>>> -		set var $stackp = $next_t.thread.esp
>>> -		set var $stack_top = ($stackp & ~4095) + 4096
>>> -		set var $stack_bot = ($stackp & ~4095)
>>> +		btthreadstruct $next_t
>>> -		set $stackp = *($stackp)
>>> -		while (($stackp < $stack_top) && ($stackp > $stack_bot))
>>> -			set var $addr = *($stackp + 4)
>>> -			info symbol $addr
>>> -			set $stackp = *($stackp)
>>> -		end
>>> -
>>> -		set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
>>> +		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
>>>   		while ($next_th != $next_t)
>>>   			set $next_th=(struct task_struct *)$next_th
>>> -			printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
>>> -			printf "===================\n"
>>> -			set var $stackp = $next_t.thread.esp
>>> -			set var $stack_top = ($stackp & ~4095) + 4096
>>> -			set var $stack_bot = ($stackp & ~4095)
>>> -
>>> -			set $stackp = *($stackp)
>>> -			while (($stackp < $stack_top) && ($stackp > $stack_bot))
>>> -				set var $addr = *($stackp + 4)
>>> -				info symbol $addr
>>> -				set $stackp = *($stackp)
>>> -			end
>>> -			set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
>>> +			btthreadstruct $next_th
>>> +			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
>>>   		end
>>>   		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
>>>   	end
>>> @@ -101,7 +102,7 @@ end
>>>   define btpid
>>>   	set var $pid = $arg0
>>>   	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
>>> -	set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
>>> +	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
>>>   	set $init_t=&init_task
>>>   	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
>>>   	set var $pid_task = 0
>>> @@ -113,29 +114,18 @@ define btpid
>>>   			set $pid_task = $next_t
>>>   		end
>>> -		set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
>>> +		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
>>>   		while ($next_th != $next_t)
>>>   			set $next_th=(struct task_struct *)$next_th
>>>   			if ($next_th.pid == $pid)
>>>   				set $pid_task = $next_th
>>>   			end
>>> -			set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
>>> +			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
>>>   		end
>>>   		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
>>>   	end
>>> -	printf "\npid %d; comm %s:\n", $pid_task.pid, $pid_task.comm
>>> -	printf "===================\n"
>>> -	set var $stackp = $pid_task.thread.esp
>>> -	set var $stack_top = ($stackp & ~4095) + 4096
>>> -	set var $stack_bot = ($stackp & ~4095)
>>> -
>>> -	set $stackp = *($stackp)
>>> -	while (($stackp < $stack_top) && ($stackp > $stack_bot))
>>> -		set var $addr = *($stackp + 4)
>>> -		info symbol $addr
>>> -		set $stackp = *($stackp)
>>> -	end
>>> +	btthreadstruct $pid_task
>>>   end
>>>   document btpid
>>>   	backtrace of pid
>>> @@ -145,7 +135,7 @@ end
>>>   define trapinfo
>>>   	set var $pid = $arg0
>>>   	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
>>> -	set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
>>> +	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
>>>   	set $init_t=&init_task
>>>   	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
>>>   	set var $pid_task = 0
>>> @@ -157,13 +147,13 @@ define trapinfo
>>>   			set $pid_task = $next_t
>>>   		end
>>> -		set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
>>> +		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
>>>   		while ($next_th != $next_t)
>>>   			set $next_th=(struct task_struct *)$next_th
>>>   			if ($next_th.pid == $pid)
>>>   				set $pid_task = $next_th
>>>   			end
>>> -			set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
>>> +			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
>>>   		end
>>>   		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
>>>   	end