On Tue 2019-01-15 14:58:15, Steven Rostedt wrote: > On Tue, 15 Jan 2019 19:54:33 +0100 > Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > > On 2019-01-15 12:39:10 [-0500], Steven Rostedt wrote: > > > --- a/kernel/printk/printk.c > > > +++ b/kernel/printk/printk.c > > > @@ -1742,6 +1742,13 @@ static int console_trylock_spinning(void) > > > if (console_trylock()) > > > return 1; > > > > > > + /* > > > + * The consoles are preemptable in PREEMPT_RT, which can cause > > > + * spinning to deadlock. > > > + */ > > > + if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL)) > > > + return 0; > > > + > > > printk_safe_enter_irqsave(flags); > > > > > > raw_spin_lock(&console_owner_lock); > > > > So my ("printk: Make rt aware") patch does: > > > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > > index 6553508ff3889..d983c509f74a2 100644 > > --- a/kernel/printk/printk.c > > +++ b/kernel/printk/printk.c > > @@ -1617,6 +1617,7 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len) > > return do_syslog(type, buf, len, SYSLOG_FROM_READER); > > } > > > > +#ifndef CONFIG_PREEMPT_RT_FULL > > /* > > * Special console_lock variants that help to reduce the risk of soft-lockups. > > * They allow to pass console_lock to another printk() call using a busy wait. > > @@ -1757,6 +1758,15 @@ static int console_trylock_spinning(void) > > return 1; > > } > > > > +#else > > + > > +static int console_trylock_spinning(void) > > +{ > > + return console_trylock(); > > +} > > + > > +#endif > > + > > /* > > * Call the console drivers, asking them to write out > > * log_buf[start] to log_buf[end - 1]. > > > > > > So it never gets into the codepath where you try to avoid spinning. > > Right? > > > > You right! Which appears to be missing from my 4.14, and I thought I > looked for that in 4.19-rt too, but I guess I was still looking at > 4.14 :-/. OK, ignore. Sorry for the noise. > > Well, it wasn't a total waste. I now know what to backport to 4.14-rt > ;-) The patch makes perfect sense. But it is not ready for upstream because CONFIG_PREEMPT_RT_FULL is not there yet. Do I get it correctly, please? Best Regards, Petr