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

Américo Wang
2011-05-12T10:43:07Z

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?

Why is %ptc better than

char comm[...];
get_task_comm(comm, current);
printk("%s: ....", comm);

?