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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Scott Wood <swood@redhat.com>
Cc: paulmck@kernel.org,
	Valentin Schneider <valentin.schneider@arm.com>,
	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>,
	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] rcutorture: Avoid problematic critical section nesting on RT
Date: Fri, 20 Aug 2021 09:11:06 +0200	[thread overview]
Message-ID: <20210820071106.fba7l6ikgo7aa6xm@linutronix.de> (raw)
In-Reply-To: <561ab28b18c31fbc221f4cb0c4df6db9b0538675.camel@redhat.com>

On 2021-08-19 23:11:12 [-0500], Scott Wood wrote:
> On Thu, 2021-08-19 at 11:20 -0700, Paul E. McKenney wrote:
> > On Thu, Aug 19, 2021 at 05:47:08PM +0200, Sebastian Andrzej Siewior wrote:
> > > On 2021-08-19 17:39:29 [+0200], To Paul E. McKenney wrote:
> > > > +	/*
> > > > +	 * Ideally these sequences would be detected in debug builds
> > > > +	 * (regardless of RT), but until then don't stop testing
> > > > +	 * them on non-RT.
> > > > +	 */
> > > > +	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
> > > > +		/*
> > > > +		 * 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
> > > > +		 * (could leak a special flag and delay reporting the qs).
> > > > +		 */
> > > > +		if ((oldmask & RCUTORTURE_RDR_RCU) &&
> > > > +		    (mask & RCUTORTURE_RDR_IRQ) &&
> > > > +		    !(mask & preempts))
> > > > +			mask |= RCUTORTURE_RDR_RCU;
> > > 
> > > This piece above, I don't understand. I had it running for a while and
> > > it didn't explode. Let me try TREE01 for 30min without that piece.
> > 
> > This might be historical.  There was a time when interrupts being
> > disabled across rcu_read_unlock() meant that preemption had to have
> > been disabled across the entire RCU read-side critical section.
> > 
> > I am not seeing a purpose for it now, but I could easily be missing
> > something, especially given my tenuous grasp of RT.
> 
> Yeah, I think this was to deal with not having the irq work stuff in RT
> at the time.

Good. Thank you for the confirmation. 
I run (without the hunk above) 2x 6h of TREE01 and 4x 6h of TREE06 and
it looked good.

> -Scott

Sebastian

WARNING: multiple messages have this Message-ID (diff)
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Scott Wood <swood@redhat.com>
Cc: paulmck@kernel.org,
	Valentin Schneider <valentin.schneider@arm.com>,
	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>,
	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] rcutorture: Avoid problematic critical section nesting on RT
Date: Fri, 20 Aug 2021 09:11:06 +0200	[thread overview]
Message-ID: <20210820071106.fba7l6ikgo7aa6xm@linutronix.de> (raw)
In-Reply-To: <561ab28b18c31fbc221f4cb0c4df6db9b0538675.camel@redhat.com>

On 2021-08-19 23:11:12 [-0500], Scott Wood wrote:
> On Thu, 2021-08-19 at 11:20 -0700, Paul E. McKenney wrote:
> > On Thu, Aug 19, 2021 at 05:47:08PM +0200, Sebastian Andrzej Siewior wrote:
> > > On 2021-08-19 17:39:29 [+0200], To Paul E. McKenney wrote:
> > > > +	/*
> > > > +	 * Ideally these sequences would be detected in debug builds
> > > > +	 * (regardless of RT), but until then don't stop testing
> > > > +	 * them on non-RT.
> > > > +	 */
> > > > +	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
> > > > +		/*
> > > > +		 * 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
> > > > +		 * (could leak a special flag and delay reporting the qs).
> > > > +		 */
> > > > +		if ((oldmask & RCUTORTURE_RDR_RCU) &&
> > > > +		    (mask & RCUTORTURE_RDR_IRQ) &&
> > > > +		    !(mask & preempts))
> > > > +			mask |= RCUTORTURE_RDR_RCU;
> > > 
> > > This piece above, I don't understand. I had it running for a while and
> > > it didn't explode. Let me try TREE01 for 30min without that piece.
> > 
> > This might be historical.  There was a time when interrupts being
> > disabled across rcu_read_unlock() meant that preemption had to have
> > been disabled across the entire RCU read-side critical section.
> > 
> > I am not seeing a purpose for it now, but I could easily be missing
> > something, especially given my tenuous grasp of RT.
> 
> Yeah, I think this was to deal with not having the irq work stuff in RT
> at the time.

Good. Thank you for the confirmation. 
I run (without the hunk above) 2x 6h of TREE01 and 4x 6h of TREE06 and
it looked good.

> -Scott

Sebastian

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  reply	other threads:[~2021-08-20  7:11 UTC|newest]

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-11 20:13 [PATCH v3 0/4] rcu, arm64: PREEMPT_RT fixlets Valentin Schneider
2021-08-11 20:13 ` Valentin Schneider
2021-08-11 20:13 ` [PATCH v3 1/4] rcutorture: Don't disable softirqs with preemption disabled when PREEMPT_RT Valentin Schneider
2021-08-11 20:13   ` Valentin Schneider
2021-08-12 16:47   ` Paul E. McKenney
2021-08-12 16:47     ` Paul E. McKenney
2021-08-17 12:13   ` Sebastian Andrzej Siewior
2021-08-17 12:13     ` Sebastian Andrzej Siewior
2021-08-17 13:17     ` Sebastian Andrzej Siewior
2021-08-17 13:17       ` Sebastian Andrzej Siewior
2021-08-17 14:40       ` [PATCH] rcutorture: Avoid problematic critical section nesting on RT Sebastian Andrzej Siewior
2021-08-17 14:40         ` Sebastian Andrzej Siewior
2021-08-18 22:46         ` Paul E. McKenney
2021-08-18 22:46           ` Paul E. McKenney
2021-08-19 15:35           ` Sebastian Andrzej Siewior
2021-08-19 15:35             ` Sebastian Andrzej Siewior
2021-08-19 15:39           ` Sebastian Andrzej Siewior
2021-08-19 15:39             ` Sebastian Andrzej Siewior
2021-08-19 15:47             ` Sebastian Andrzej Siewior
2021-08-19 15:47               ` Sebastian Andrzej Siewior
2021-08-19 18:20               ` Paul E. McKenney
2021-08-19 18:20                 ` Paul E. McKenney
2021-08-19 18:45                 ` Sebastian Andrzej Siewior
2021-08-19 18:45                   ` Sebastian Andrzej Siewior
2021-08-20  4:11                 ` Scott Wood
2021-08-20  4:11                   ` Scott Wood
2021-08-20  7:11                   ` Sebastian Andrzej Siewior [this message]
2021-08-20  7:11                     ` Sebastian Andrzej Siewior
2021-08-20  7:42                   ` [PATCH v2] rcutorture: Avoid problematic critical section nesting on PREEMPT_RT Sebastian Andrzej Siewior
2021-08-20  7:42                     ` Sebastian Andrzej Siewior
2021-08-20 22:10                     ` Paul E. McKenney
2021-08-20 22:10                       ` Paul E. McKenney
2021-08-20  3:23         ` [PATCH] rcutorture: Avoid problematic critical section nesting on RT Scott Wood
2021-08-20  3:23           ` Scott Wood
2021-08-20  6:54           ` Sebastian Andrzej Siewior
2021-08-20  6:54             ` Sebastian Andrzej Siewior
2021-08-11 20:13 ` [PATCH v3 2/4] sched: Introduce migratable() Valentin Schneider
2021-08-11 20:13   ` Valentin Schneider
2021-08-17 14:43   ` Sebastian Andrzej Siewior
2021-08-17 14:43     ` Sebastian Andrzej Siewior
2021-08-22 17:31     ` Valentin Schneider
2021-08-22 17:31       ` Valentin Schneider
2021-08-17 17:09   ` Sebastian Andrzej Siewior
2021-08-17 17:09     ` Sebastian Andrzej Siewior
2021-08-17 19:30     ` Phil Auld
2021-08-17 19:30       ` Phil Auld
2021-08-22 18:14     ` Valentin Schneider
2021-08-22 18:14       ` Valentin Schneider
2022-01-26 16:56       ` Sebastian Andrzej Siewior
2022-01-26 16:56         ` Sebastian Andrzej Siewior
2022-01-26 18:10         ` Valentin Schneider
2022-01-26 18:10           ` Valentin Schneider
2022-01-27 10:07           ` Sebastian Andrzej Siewior
2022-01-27 10:07             ` Sebastian Andrzej Siewior
2022-01-27 18:23             ` Valentin Schneider
2022-01-27 18:23               ` Valentin Schneider
2022-01-27 19:27         ` Valentin Schneider
2022-01-27 19:27           ` Valentin Schneider
2022-02-04  9:24           ` Sebastian Andrzej Siewior
2022-02-04  9:24             ` Sebastian Andrzej Siewior
2021-08-11 20:13 ` [PATCH v3 3/4] rcu/nocb: Protect NOCB state via local_lock() under PREEMPT_RT Valentin Schneider
2021-08-11 20:13   ` Valentin Schneider
2021-08-13  0:20   ` Paul E. McKenney
2021-08-13  0:20     ` Paul E. McKenney
2021-08-13 18:48     ` Valentin Schneider
2021-08-13 18:48       ` Valentin Schneider
2021-08-24 13:00     ` Frederic Weisbecker
2021-08-17 15:36   ` Sebastian Andrzej Siewior
2021-08-17 15:36     ` Sebastian Andrzej Siewior
2021-08-22 18:15     ` Valentin Schneider
2021-08-22 18:15       ` Valentin Schneider
2021-09-21 14:05   ` Thomas Gleixner
2021-09-21 14:05     ` Thomas Gleixner
2021-09-21 21:12     ` rcu/tree: Protect rcu_rdp_is_offloaded() invocations on RT Thomas Gleixner
2021-09-21 23:36       ` Frederic Weisbecker
2021-09-21 23:36         ` Frederic Weisbecker
2021-09-22  2:18         ` Paul E. McKenney
2021-09-22  2:18           ` Paul E. McKenney
2021-09-22 11:31           ` Frederic Weisbecker
2021-09-22 11:31             ` Frederic Weisbecker
2021-09-21 23:45       ` Frederic Weisbecker
2021-09-21 23:45         ` Frederic Weisbecker
2021-09-22  6:32         ` Sebastian Andrzej Siewior
2021-09-22  6:32           ` Sebastian Andrzej Siewior
2021-09-22 11:10           ` Frederic Weisbecker
2021-09-22 11:10             ` Frederic Weisbecker
2021-09-22 11:27             ` Sebastian Andrzej Siewior
2021-09-22 11:27               ` Sebastian Andrzej Siewior
2021-09-22 11:38               ` Frederic Weisbecker
2021-09-22 11:38                 ` Frederic Weisbecker
2021-09-22 13:02                 ` Sebastian Andrzej Siewior
2021-09-22 13:02                   ` Sebastian Andrzej Siewior
2021-09-23 10:02                   ` Frederic Weisbecker
2021-09-23 10:02                     ` Frederic Weisbecker
2021-09-30  9:00       ` Valentin Schneider
2021-09-30  9:00         ` Valentin Schneider
2021-09-30 10:53         ` Frederic Weisbecker
2021-09-30 10:53           ` Frederic Weisbecker
2021-09-30 13:22           ` Valentin Schneider
2021-09-30 13:22             ` Valentin Schneider
2021-08-11 20:13 ` [PATCH v3 4/4] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider
2021-08-11 20:13   ` Valentin Schneider

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