Messages in this thread | | | Date | Thu, 11 Nov 2021 13:13:15 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 1/1] printk: suppress rcu stall warnings caused by slow console devices |
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On Thu, Nov 11, 2021 at 04:59:04PM -0300, Wander Lairson Costa wrote: > If we have a reasonable large dataset to flush in the printk ring > buffer in the presence of a slow console device (like a serial port > with a low baud rate configured), the RCU stall detector may report > warnings. > > This patch suppresses RCU stall warnings while flushing the ring buffer > to the console. > > Signed-off-by: Wander Lairson Costa <wander@redhat.com>
From an RCU perspective:
Acked-by: Paul E. McKenney <paulmck@kernel.org>
> --- > kernel/printk/printk.c | 24 +++++++++++++++++++++++- > 1 file changed, 23 insertions(+), 1 deletion(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index cbc35d586afb..42b622454314 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2588,6 +2588,20 @@ static inline int can_use_console(void) > return cpu_online(raw_smp_processor_id()) || have_callable_console(); > } > > +extern int rcu_cpu_stall_suppress; > + > +static void rcu_console_stall_suppress(void) > +{ > + if (!rcu_cpu_stall_suppress) > + rcu_cpu_stall_suppress = 4; > +} > + > +static void rcu_console_stall_unsuppress(void) > +{ > + if (rcu_cpu_stall_suppress == 4) > + rcu_cpu_stall_suppress = 0; > +} > + > /** > * console_unlock - unlock the console system > * > @@ -2634,6 +2648,9 @@ void console_unlock(void) > * and cleared after the "again" goto label. > */ > do_cond_resched = console_may_schedule; > + > + rcu_console_stall_suppress(); > + > again: > console_may_schedule = 0; > > @@ -2645,6 +2662,7 @@ void console_unlock(void) > if (!can_use_console()) { > console_locked = 0; > up_console_sem(); > + rcu_console_stall_unsuppress(); > return; > } > > @@ -2716,8 +2734,10 @@ void console_unlock(void) > > handover = console_lock_spinning_disable_and_check(); > printk_safe_exit_irqrestore(flags); > - if (handover) > + if (handover) { > + rcu_console_stall_unsuppress(); > return; > + } > > if (do_cond_resched) > cond_resched(); > @@ -2738,6 +2758,8 @@ void console_unlock(void) > retry = prb_read_valid(prb, next_seq, NULL); > if (retry && console_trylock()) > goto again; > + > + rcu_console_stall_unsuppress(); > } > EXPORT_SYMBOL(console_unlock); > > -- > 2.27.0 >
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