linux-kernel - Re: [PATCH] rcu: Fix missing TICK_DEP_MASK_RCU

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Date:   Wed, 21 Dec 2022 12:16:34 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: Fix missing TICK_DEP_MASK_RCU_EXP dependency check

On Tue, Dec 20, 2022 at 10:16:25PM +0800, Zqiang wrote:
> This commit add TICK_DEP_MASK_RCU_EXP dependency check in
> check_tick_dependency(), fix commit df1e849ae4559 ("rcu: Enable
> tick for nohz_full CPUs slow to provide expedited QS").
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>

Again, good eyes, thank you!!!

I have queued this for further review and testing, given that it affects
pretty much only RCU.  However, if someone else would rather take it:

Acked-by: Paul E. McKenney <paulmck@...nel.org>

							Thanx, Paul

------------------------------------------------------------------------

commit f22caef6cda5ed19a55ec2e703f60f1fa85e52bc
Author: Zqiang <qiang1.zhang@...el.com>
Date:   Tue Dec 20 22:16:25 2022 +0800

    rcu: Fix missing TICK_DEP_MASK_RCU_EXP dependency check
    
    This commit adds checks for the TICK_DEP_MASK_RCU_EXP bit, thus enabling
    RCU expedited grace periods to actually force-enable scheduling-clock
    interrupts on holdout CPUs.
    
    Fixes: df1e849ae455 ("rcu: Enable tick for nohz_full CPUs slow to provide expedited QS")
    Signed-off-by: Zqiang <qiang1.zhang@...el.com>
    Cc: Steven Rostedt <rostedt@...dmis.org>
    Cc: Masami Hiramatsu <mhiramat@...nel.org>
    Cc: Frederic Weisbecker <fweisbec@...il.com>
    Cc: Thomas Gleixner <tglx@...utronix.de>
    Cc: Ingo Molnar <mingo@...nel.org>
    Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index 2e713a7d9aa3a..3e8619c72f774 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -371,7 +371,8 @@ TRACE_EVENT(itimer_expire,
 		tick_dep_name(PERF_EVENTS)		\
 		tick_dep_name(SCHED)			\
 		tick_dep_name(CLOCK_UNSTABLE)		\
-		tick_dep_name_end(RCU)
+		tick_dep_name(RCU)			\
+		tick_dep_name_end(RCU_EXP)
 
 #undef tick_dep_name
 #undef tick_dep_mask_name
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b0e3c9205946f..ba2ac1469d473 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -281,6 +281,11 @@ static bool check_tick_dependency(atomic_t *dep)
 		return true;
 	}
 
+	if (val & TICK_DEP_MASK_RCU_EXP) {
+		trace_tick_stop(0, TICK_DEP_MASK_RCU_EXP);
+		return true;
+	}
+
 	return false;
 }