On (19/11/18 16:27), Petr Mladek wrote:
> > > @@ -2027,8 +2027,11 @@ asmlinkage int vprintk_emit(int facility, int level,
> > > pending_output = (curr_log_seq != log_next_seq);
> > > logbuf_unlock_irqrestore(flags);
> > >
> > > + if (!pending_output)
> > > + return printed_len;
> > > +
> > > /* If called from the scheduler, we can not call up(). */
> > > - if (!in_sched && pending_output) {
> > > + if (!in_sched) {
> > > /*
> > > * Disable preemption to avoid being preempted while holding
> > > * console_sem which would prevent anyone from printing to
> > > @@ -2043,10 +2046,11 @@ asmlinkage int vprintk_emit(int facility, int level,
> > > if (console_trylock_spinning())
> > > console_unlock();
> > > preempt_enable();
> > > - }
> > >
> > > - if (pending_output)
> > > + wake_up_interruptible(&log_wait);
>
> I do not like this. As a result, normal printk() will always deadlock
> in the scheduler code, including WARN() calls. The chance of the
> deadlock is small now. It happens only when there is another
> process waiting for console_sem.
Why would it *always* deadlock? If this is the case, why we don't *always*
deadlock doing the very same wake_up_process() from console_unlock()?
-ss
