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SubjectRe: [PATCH] tracing: Do not synchronize freeing of trigger filter on boot up
On Wed, Dec 14, 2022 at 03:37:13PM -0500, Mathieu Desnoyers wrote:
> On 2022-12-14 15:03, Paul E. McKenney wrote:
> > On Wed, Dec 14, 2022 at 08:49:54AM +0900, Masami Hiramatsu wrote:
> > > On Tue, 13 Dec 2022 17:24:29 -0500
> > > Steven Rostedt <rostedt@goodmis.org> wrote:
> > >
> > > > From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> > > >
> > > > If a trigger filter on the kernel command line fails to apply (due to
> > > > syntax error), it will be freed. The freeing will call
> > > > tracepoint_synchronize_unregister(), but this is not needed during early
> > > > boot up, and will even trigger a lockdep splat.
> > > >
> > > > Avoid calling the synchronization function when system_state is
> > > > SYSTEM_BOOTING.
> > >
> > > Shouldn't this be done inside tracepoint_synchronize_unregister()?
> > > Then, it will prevent similar warnings if we expand boot time feature.
> >
> > How about the following wide-spectrum fix within RCU_LOCKDEP_WARN()?
> > Just in case there are ever additional issues of this sort?
>
> Hi Paul,
>
> Your approach makes sense. Thanks for looking into this.
>
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Thank you, I will apply this on my next rebase.

Thanx, Paul

> > ------------------------------------------------------------------------
> >
> > commit d493ffca2df6c1963bd1d7b8f8c652a172f095ae
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date: Wed Dec 14 11:41:44 2022 -0800
> >
> > rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks
> > Currently, RCU_LOCKDEP_WARN() checks the condition before checking
> > to see if lockdep is still enabled. This is necessary to avoid the
> > false-positive splats fixed by commit 3066820034b5dd ("rcu: Reject
> > RCU_LOCKDEP_WARN() false positives"). However, the current state can
> > result in false-positive splats during early boot before lockdep is fully
> > initialized. This commit therefore checks debug_lockdep_rcu_enabled()
> > both before and after checking the condition, thus avoiding both sets
> > of false-positive error reports.
> > Reported-by: Steven Rostedt <rostedt@goodmis.org>
> > Reported-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Cc: Boqun Feng <boqun.feng@gmail.com>
> > Cc: Matthew Wilcox <willy@infradead.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> >
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index aa1b1c3546d7a..1aec1d53b0c91 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -364,11 +364,18 @@ static inline int debug_lockdep_rcu_enabled(void)
> > * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
> > * @c: condition to check
> > * @s: informative message
> > + *
> > + * This checks debug_lockdep_rcu_enabled() before checking (c) to
> > + * prevent early boot splats due to lockdep not yet being initialized,
> > + * and rechecks it after checking (c) to prevent false-positive splats
> > + * due to races with lockdep being disabled. See commit 3066820034b5dd
> > + * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
> > */
> > #define RCU_LOCKDEP_WARN(c, s) \
> > do { \
> > static bool __section(".data.unlikely") __warned; \
> > - if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \
> > + if (debug_lockdep_rcu_enabled() && (c) && \
> > + debug_lockdep_rcu_enabled() && !__warned) { \
> > __warned = true; \
> > lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
> > } \
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>

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