Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm

Américo Wang
2011-05-12T10:45:07Z

On Thu, May 12, 2011 at 6:43 PM, Américo Wang <xiyou.wangcong@gmail.com> wrote:
> On Thu, May 12, 2011 at 5:02 AM, John Stultz <john.stultz@linaro.org> wrote:
>> On Wed, 2011-05-11 at 17:33 +0800, Américo Wang wrote:
>>> On Wed, May 11, 2011 at 8:23 AM, John Stultz <john.stultz@linaro.org> wrote:
>>> > Acessing task->comm requires proper locking. However in the past
>>> > access to current->comm could be done without locking. This
>>> > is no longer the case, so all comm access needs to be done
>>> > while holding the comm_lock.
>>> >
>>> > In my attempt to clean up unprotected comm access, I've noticed
>>> > most comm access is done for printk output. To simpify correct
>>> > locking in these cases, I've introduced a new %ptc format,
>>> > which will safely print the corresponding task's comm.
>>> >
>>> > Example use:
>>> > printk("%ptc: unaligned epc - sending SIGBUS.\n", current);
>>> >
>>>
>>> Why do you hide current->comm behide printk?
>>> How is this better than printk("%s: ....", task_comm(current)) ?
>>
>> So to properly access current->comm, you need to hold the task-lock (or
>> with my new patch set, the comm_lock). Rather then adding locking to all
>> the call sites that printk("%s ...", current->comm), I'm suggesting we
>> add a new %ptc method which will handle the locking for you.
>>
>
> Sorry, I meant why not adding the locking into a wrapper function,
> probably get_task_comm() and let the users to call it directly?
>

Ahhh, never mind, I see the points now... Then it is fine. :)