Subject: [PATCH] kprobes: bugfix: set kprobes_all_disarmed earlier to enable re-optimization.

From: [email-masked] (Masami Hiramatsu)
Date: Tue, 20 Jan 2015 16:12:13 +0900

(2015/01/20 12:02), Wang Nan wrote:
> On 2015/1/12 19:24, Masami Hiramatsu wrote:
>> (2015/01/05 21:31), Wang Nan wrote:
>>> In original code, the probed instruction doesn't get optimized after
>>>
>>> echo 0 > /sys/kernel/debug/kprobes/enabled
>>> echo 1 > /sys/kernel/debug/kprobes/enabled
>>>
>>> This is because original code checks kprobes_all_disarmed in
>>> optimize_kprobe(), but this flag is turned off after calling that
>>> function. Therefore, optimize_kprobe() will see
>>> kprobes_all_disarmed == true and doesn't do the optimization.
>>
>> OK, a workaround is to disable/enable optimizing via sysctl.
>>
>>>
>>> This patch simply turns off kprobes_all_disarmed earlier to enable
>>> optimization.
>>>
>>
>> Anyway, thank you for finding that! :)
>>
>> Acked-by: Masami Hiramatsu <[email-masked]>
>>
> 
> Hi Masami Hiramatsu,
> 
> What about this patch? Are you still thinking on it like
> '[PATCH] kprobes: bugfix: checks kprobes_all_disarmed in unoptimized_kprobe()' ?

Without this patch.
-----
[root at localhost tracing]# echo p do_fork+5 > kprobe_events
[root at localhost tracing]# echo 1 > events/kprobes/p_do_fork_5/enable
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bd055  k  do_fork+0x5    [OPTIMIZED]
[root at localhost tracing]# echo 0 > /sys/kernel/debug/kprobes/enabled
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bd055  k  do_fork+0x5
[root at localhost tracing]# echo 1 > /sys/kernel/debug/kprobes/enabled
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bd055  k  do_fork+0x5
------
With this patch.
------
[root at localhost tracing]# echo p do_fork+5 > kprobe_events
[root at localhost tracing]# echo 1 > events/kprobes/enable
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bc1c5  k  do_fork+0x5    [OPTIMIZED]
[root at localhost tracing]# echo 0 > ../kprobes/enabled
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bc1c5  k  do_fork+0x5
[root at localhost tracing]# echo 1 > ../kprobes/enabled
[root at localhost tracing]# cat ../kprobes/list
ffffffff810bc1c5  k  do_fork+0x5    [OPTIMIZED]
------

So, looks OK to me too ;)

Acked-by: Masami Hiramatsu <[email-masked]>
Tested-by: Masami Hiramatsu <[email-masked]>

Ingo,
Could you also pull this patch to your -tip tree?

Thank you,

> 
> Thank you.
> 
>>
>>> Signed-off-by: Wang Nan <[email-masked]>
>>> ---
>>>  kernel/kprobes.c | 7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
>>> index bad4e95..b185464 100644
>>> --- a/kernel/kprobes.c
>>> +++ b/kernel/kprobes.c
>>> @@ -2320,6 +2320,12 @@ static void arm_all_kprobes(void)
>>>  	if (!kprobes_all_disarmed)
>>>  		goto already_enabled;
>>>  
>>> +	/*
>>> +	 * optimize_kprobe() called by arm_kprobe() checks
>>> +	 * kprobes_all_disarmed, so set kprobes_all_disarmed before
>>> +	 * arm_kprobe.
>>> +	 */
>>> +	kprobes_all_disarmed = false;
>>>  	/* Arming kprobes doesn't optimize kprobe itself */
>>>  	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
>>>  		head = &kprobe_table[i];
>>> @@ -2328,7 +2334,6 @@ static void arm_all_kprobes(void)
>>>  				arm_kprobe(p);
>>>  	}
>>>  
>>> -	kprobes_all_disarmed = false;
>>>  	printk(KERN_INFO "Kprobes globally enabled\n");
>>>  
>>>  already_enabled:
>>>
>>
>>
> 
> 
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-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt at hitachi.com