Re: [RFC][PATCH][kprobe] enabling booster on the preemptible kernel, take 2

["bibo,mao" <bibo_mao@linux.intel.com>]

Masami Hiramatsu wrote:
> Hi bibo,
> 
> Thank you for your review!
> 
> bibo,mao wrote:
>> This patch will boost kprobe on preemptible kernel, I think
>> it is deserved to waster some memory for better performance
>> by deferring memory free after freeze_processes.
> 
> I think it doesn't waste memory so much, because it tries
> to reuse garbage memories before the kernel allocates an
> additional page.
> 
> [...]
>>> +static int __kprobes collect_garbage_slots(void)
>>> +{
>>> +       struct kprobe_insn_page *kip;
>>> +       struct hlist_node *pos, *next;
>>> +       int ret = -1;
>>> +
>>> +#if defined(CONFIG_PREEMPT) && defined(CONFIG_PM)
>>> +       /* Ensure no-one is preepmted on the garbages */
>>> +       if (freeze_processes() != 0)
>> I do not know whether there exists non-freezeable and preemptive kernel
>> thread, if there exist then this thread will not be frozen.
> 
> In that case, freeze_processes() returns the positive value which
> means how many processes are not frozen. If freeze_processes()
> returns non-zero, this function aborts the garbage collection.
> 
But from the code, return value of freeze_processes() represents how many
processes can be frozen but are not frozen. I grep the kernel code, there
still exists many processes which flag is PF_NOFREEZE.
I think if current probed thread is PF_NOFREEZE, then kprobe_handler need 
skip the bootser.

thanks
bibo,mao