Messages in this thread Patch in this message | | | Date | Fri, 27 May 2016 16:56:01 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH RT] kernel/printk: Don't try to print from IRQ/NMI region |
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* Steven Rostedt | 2016-05-27 10:12:51 [-0400]:
>On Fri, 27 May 2016 15:58:12 +0200 >Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > >> On -RT we try to acquire sleeping locks which might lead to warnings >> from lockdep or a warn_on() from spin_try_lock() (which is a rtmutex on >> RT). >> We don't print in general from a IRQ off region so we should not try >> this via console_unblank() / bust_spinlocks() as well. >> >> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> >> --- >> kernel/printk/printk.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -1502,6 +1502,11 @@ static void call_console_drivers(int lev >> if (!console_drivers) >> return; >> >> + if (IS_ENABLED(CONFIG_PREEMPT_RT_BASE)) { >> + if (in_irq() || in_nmi()) >> + return; >> + } >> + > >We use to have a patch where a console could flag itself as atomic. >That is, that it doesn't call any sleeping locks. What happened to that. > >IIRC, the video console was one such console. Otherwise, we lose out on >backtraces in irq context.
video, like VT? The call_console_drivers() does not check such a flag and I don't remember about removing something like that. I was actually thinking about adding such a flag… I remember you had something in your tree to print from IRQ off regions via UART.
We don't print from a context with interrupts disabled or even a preempt disabled region. In such cases we just wake_up_klogd() and print it later. The reason for the patch was the HW/SW lockup detector which comes with interrupts disabled or NMI context and gets to the console(s). Usually we defer everything until later except in this case. And I got busted later in the VT code (and the problem was that one sleeping while atomic warning which led to more stuff to be printed).
Sebastian
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