Re: [PATCH v3 1/4] rcutorture: Don't disable softirqs with preemption disabled when PREEMPT_RT

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org,
	linux-rt-users@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Steven Price <steven.price@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>, Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH v3 1/4] rcutorture: Don't disable softirqs with preemption disabled when PREEMPT_RT
Date: Tue, 17 Aug 2021 15:17:41 +0200	[thread overview]
Message-ID: <20210817131741.evduh4fw7vyv2dzt@linutronix.de> (raw)
In-Reply-To: <20210817121345.5iyj5epemczn3a52@linutronix.de>

On 2021-08-17 14:13:47 [+0200], To Valentin Schneider wrote:
> > index eecd1caef71d..4f3db1d3170d 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -1548,6 +1548,8 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
> >  	 * them on non-RT.
> >  	 */
> >  	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
> > +		/* Can't disable bh in atomic context under PREEMPT_RT */
> > +		mask &= ~(RCUTORTURE_RDR_ATOM_BH | RCUTORTURE_RDR_ATOM_RBH);
> 
> Let me stare at this…

I would fold this

--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1549,6 +1549,13 @@ rcutorture_extend_mask(int oldmask, stru
 	 */
 	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
 		/*
+		 * Can't disable bh in atomic context if bh was already
+		 * disabled by another task on the same CPU. Instead of
+		 * attempting to track this, just avoid disabling bh in atomic
+		 * context.
+		 */
+		mask &= ~atomic_bhs;
+		/*
 		 * Can't release the outermost rcu lock in an irq disabled
 		 * section without preemption also being disabled, if irqs
 		 * had ever been enabled during this RCU critical section
@@ -1559,16 +1566,6 @@ rcutorture_extend_mask(int oldmask, stru
 		    !(mask & preempts))
 			mask |= RCUTORTURE_RDR_RCU;
 
-		/* Can't modify atomic bh in non-atomic context */
-		if ((oldmask & atomic_bhs) && (mask & atomic_bhs) &&
-		    !(mask & preempts_irq)) {
-			mask |= oldmask & preempts_irq;
-			if (mask & RCUTORTURE_RDR_IRQ)
-				mask |= oldmask & tmp;
-		}
-		if ((mask & atomic_bhs) && !(mask & preempts_irq))
-			mask |= RCUTORTURE_RDR_PREEMPT;
-
 		/* Can't modify non-atomic bh in atomic context */
 		tmp = nonatomic_bhs;
 		if (oldmask & preempts_irq)

into the original patch and forward it upstream…

Sebastian
