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SubjectRe: [patch] mm, hugetlb: add thread name and pid to SHM_HUGETLB mlock rlimit warning
On Thu, 8 Mar 2012 13:37:57 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> On Thu, 8 Mar 2012, Andrew Morton wrote:
>
> > > --- a/fs/hugetlbfs/inode.c
> > > +++ b/fs/hugetlbfs/inode.c
> > > @@ -946,7 +946,11 @@ struct file *hugetlb_file_setup(const char *name, size_t size,
> > > if (creat_flags == HUGETLB_SHMFS_INODE && !can_do_hugetlb_shm()) {
> > > *user = current_user();
> > > if (user_shm_lock(size, *user)) {
> > > - printk_once(KERN_WARNING "Using mlock ulimits for SHM_HUGETLB is deprecated\n");
> > > + task_lock(current);
> > > + printk_once(KERN_WARNING
> > > + "%s (%d): Using mlock ulimits for SHM_HUGETLB is deprecated\n",
> > > + current->comm, current->pid);
> > > + task_unlock(current);
> >
> > I assume the task_lock() is there to protect current->comm.
>
> Yup.
>
> > If so, it
> > is unneeded - we're protecting against prctl(PR_SET_NAME), and
> > PR_SET_NAME only operates on current, and we know this task isn't
> > currently running PR_SET_NAME.
> >
> > If there's a way for another task to alter this task's ->comm then we
> > _do_ need locking. But there isn't a way, I hope.
> >
>
> I wish there wasn't as well, it would prevent a lot of the currently buggy
> reads to current->comm and allow us to avoid so many otherwise pointless
> task_lock()s.
>
> This protects against /proc/pid/comm, which is writable by threads in the
> same thread group.

Oh crap.

> We have a get_task_comm() that does the task_lock()
> internally but requires a TASK_COMM_LEN buffer in the calling code. It's
> just easier for the calling code to the task_lock() itself for a tiny
> little printk().

Well for a tiny little printk we could just omit the locking? The
printk() won't oops and once in a million years one person will see a
garbled comm[] string?



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