Re: [PATCH 5/5] kernel/kthread: show a warning if kthread's comm is still trucated

[Yafang Shao]

On Thu, Sep 30, 2021 at 11:17 PM Petr Mladek <pmladek@xxxxxxxx> wrote:
>
> On Wed 2021-09-29 11:50:36, Yafang Shao wrote:
> > Show a warning if the ktrhead's comm is still trucated. Below is the
> > result of my test case -
> >
> > __kthread_create_on_node:410: comm of pid 14 is truncated from "I-am-a-kthread-with-long-name" to "I-am-a-kthread-with-lon"
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > ---
> >  kernel/kthread.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/kthread.c b/kernel/kthread.c
> > index 6def951c605a..aa093f1f423a 100644
> > --- a/kernel/kthread.c
> > +++ b/kernel/kthread.c
> > @@ -404,7 +404,11 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
> >                * task is already visible to other tasks, so updating
> >                * COMM must be protected.
> >                */
> > -             vsnprintf(name, sizeof(name), namefmt, args);
> > +             if (vsnprintf(name, KTHREAD_COMM_LEN, namefmt, args) >=
> > +                 KTHREAD_COMM_LEN)
> > +                     pr_warn("%s:%d: comm of pid %d is truncated from \"%s\" to \"%s\"\n",
> > +                             __func__, __LINE__, task->pid, namefmt, name);
>
> The warning makes sense. But the use of "namefmt" looks wrong. It is
> format and not the name. Also __func__ and __LINE__ is overkill. It will
> be always the same.
>
> I would do something like:
>
>                 len = vsnprintf(name, sizeof(name), namefmt, args);
>                 if (len >= KTHREAD_COMM_LEN) {
>                         pr_warn("truncated kthread comm:%s, pid:%d by %d characters\n",
>                                 name, task->pid, len - KTHREAD_COMM_LEN + 1);
>                 }
>

Thanks for the suggestion. I will change it.

-- 
Thanks
Yafang