From: "Paul E. McKenney" <paulmck@kernel.org> To: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Scott Wood <swood@redhat.com>, 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 v2] rcutorture: Avoid problematic critical section nesting on PREEMPT_RT Date: Fri, 20 Aug 2021 15:10:56 -0700 [thread overview] Message-ID: <20210820221056.GL4126399@paulmck-ThinkPad-P17-Gen-1> (raw) In-Reply-To: <20210820074236.2zli4nje7bof62rh@linutronix.de> On Fri, Aug 20, 2021 at 09:42:36AM +0200, Sebastian Andrzej Siewior wrote: > From: "From: Scott Wood" <swood@redhat.com> > > rcutorture is generating some nesting scenarios that are not compatible on PREEMPT_RT. > For example: > preempt_disable(); > rcu_read_lock_bh(); > preempt_enable(); > rcu_read_unlock_bh(); > > The problem here is that on PREEMPT_RT the bottom halves have to be > disabled and enabled in preemptible context. > > Reorder locking: start with BH locking and continue with then with > disabling preemption or interrupts. In the unlocking do it reverse by > first enabling interrupts and preemption and BH at the very end. > Ensure that on PREEMPT_RT BH locking remains unchanged if in > non-preemptible context. > > Link: https://lkml.kernel.org/r/20190911165729.11178-6-swood@redhat.com > Link: https://lkml.kernel.org/r/20210819182035.GF4126399@paulmck-ThinkPad-P17-Gen-1 > Signed-off-by: Scott Wood <swood@redhat.com> > [bigeasy: Drop ATOM_BH, make it only about changing BH in atomic > context. Allow enabling RCU in IRQ-off section. Reword commit message.] > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Looks plausible. ;-) I have queued this for testing and further review. If all goes well, perhaps the v5.16 merge window. Thanx, Paul > --- > v1…v2: > - Drop the ATOM_BH* bits. There don't seem to be needed, Paul did not > ant the preempt-disable around enabling/disabling BH as it might fix > things that RCU should take care. > > - Allow enabling RCU with disabled interrupts on RT. Scott confirmed > that it was needed but might no longer be needed. Paul said that it > might have been required at some point. It survived multiple 6h long > TREE01 and TREE06 testing. > > kernel/rcu/rcutorture.c | 48 ++++++++++++++++++++++++++++++----------- > 1 file changed, 36 insertions(+), 12 deletions(-) > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > index 40ef5417d9545..d2ef535530b10 100644 > --- a/kernel/rcu/rcutorture.c > +++ b/kernel/rcu/rcutorture.c > @@ -1432,28 +1432,34 @@ static void rcutorture_one_extend(int *readstate, int newstate, > /* First, put new protection in place to avoid critical-section gap. */ > if (statesnew & RCUTORTURE_RDR_BH) > local_bh_disable(); > + if (statesnew & RCUTORTURE_RDR_RBH) > + rcu_read_lock_bh(); > if (statesnew & RCUTORTURE_RDR_IRQ) > local_irq_disable(); > if (statesnew & RCUTORTURE_RDR_PREEMPT) > preempt_disable(); > - if (statesnew & RCUTORTURE_RDR_RBH) > - rcu_read_lock_bh(); > if (statesnew & RCUTORTURE_RDR_SCHED) > rcu_read_lock_sched(); > if (statesnew & RCUTORTURE_RDR_RCU) > idxnew = cur_ops->readlock() << RCUTORTURE_RDR_SHIFT; > > - /* Next, remove old protection, irq first due to bh conflict. */ > + /* > + * Next, remove old protection, in decreasing order of strength > + * to avoid unlock paths that aren't safe in the stronger > + * context. Namely: BH can not be enabled with disabled interrupts. > + * Additionally PREEMPT_RT requires that BH is enabled in preemptible > + * context. > + */ > if (statesold & RCUTORTURE_RDR_IRQ) > local_irq_enable(); > - if (statesold & RCUTORTURE_RDR_BH) > - local_bh_enable(); > if (statesold & RCUTORTURE_RDR_PREEMPT) > preempt_enable(); > - if (statesold & RCUTORTURE_RDR_RBH) > - rcu_read_unlock_bh(); > if (statesold & RCUTORTURE_RDR_SCHED) > rcu_read_unlock_sched(); > + if (statesold & RCUTORTURE_RDR_BH) > + local_bh_enable(); > + if (statesold & RCUTORTURE_RDR_RBH) > + rcu_read_unlock_bh(); > if (statesold & RCUTORTURE_RDR_RCU) { > bool lockit = !statesnew && !(torture_random(trsp) & 0xffff); > > @@ -1496,6 +1502,9 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp) > int mask = rcutorture_extend_mask_max(); > unsigned long randmask1 = torture_random(trsp) >> 8; > unsigned long randmask2 = randmask1 >> 3; > + unsigned long preempts = RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED; > + unsigned long preempts_irq = preempts | RCUTORTURE_RDR_IRQ; > + unsigned long bhs = RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH; > > WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT); > /* Mostly only one bit (need preemption!), sometimes lots of bits. */ > @@ -1503,11 +1512,26 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp) > mask = mask & randmask2; > else > mask = mask & (1 << (randmask2 % RCUTORTURE_RDR_NBITS)); > - /* Can't enable bh w/irq disabled. */ > - if ((mask & RCUTORTURE_RDR_IRQ) && > - ((!(mask & RCUTORTURE_RDR_BH) && (oldmask & RCUTORTURE_RDR_BH)) || > - (!(mask & RCUTORTURE_RDR_RBH) && (oldmask & RCUTORTURE_RDR_RBH)))) > - mask |= RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH; > + > + /* > + * Can't enable bh w/irq disabled. > + */ > + if (mask & RCUTORTURE_RDR_IRQ) > + mask |= oldmask & bhs; > + > + /* > + * 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 modify BH in atomic context */ > + if (oldmask & preempts_irq) > + mask &= ~bhs; > + if ((oldmask | mask) & preempts_irq) > + mask |= oldmask & bhs; > + } > + > return mask ?: RCUTORTURE_RDR_RCU; > } > > -- > 2.33.0 >
WARNING: multiple messages have this Message-ID (diff)
From: "Paul E. McKenney" <paulmck@kernel.org> To: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Scott Wood <swood@redhat.com>, 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 v2] rcutorture: Avoid problematic critical section nesting on PREEMPT_RT Date: Fri, 20 Aug 2021 15:10:56 -0700 [thread overview] Message-ID: <20210820221056.GL4126399@paulmck-ThinkPad-P17-Gen-1> (raw) In-Reply-To: <20210820074236.2zli4nje7bof62rh@linutronix.de> On Fri, Aug 20, 2021 at 09:42:36AM +0200, Sebastian Andrzej Siewior wrote: > From: "From: Scott Wood" <swood@redhat.com> > > rcutorture is generating some nesting scenarios that are not compatible on PREEMPT_RT. > For example: > preempt_disable(); > rcu_read_lock_bh(); > preempt_enable(); > rcu_read_unlock_bh(); > > The problem here is that on PREEMPT_RT the bottom halves have to be > disabled and enabled in preemptible context. > > Reorder locking: start with BH locking and continue with then with > disabling preemption or interrupts. In the unlocking do it reverse by > first enabling interrupts and preemption and BH at the very end. > Ensure that on PREEMPT_RT BH locking remains unchanged if in > non-preemptible context. > > Link: https://lkml.kernel.org/r/20190911165729.11178-6-swood@redhat.com > Link: https://lkml.kernel.org/r/20210819182035.GF4126399@paulmck-ThinkPad-P17-Gen-1 > Signed-off-by: Scott Wood <swood@redhat.com> > [bigeasy: Drop ATOM_BH, make it only about changing BH in atomic > context. Allow enabling RCU in IRQ-off section. Reword commit message.] > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Looks plausible. ;-) I have queued this for testing and further review. If all goes well, perhaps the v5.16 merge window. Thanx, Paul > --- > v1…v2: > - Drop the ATOM_BH* bits. There don't seem to be needed, Paul did not > ant the preempt-disable around enabling/disabling BH as it might fix > things that RCU should take care. > > - Allow enabling RCU with disabled interrupts on RT. Scott confirmed > that it was needed but might no longer be needed. Paul said that it > might have been required at some point. It survived multiple 6h long > TREE01 and TREE06 testing. > > kernel/rcu/rcutorture.c | 48 ++++++++++++++++++++++++++++++----------- > 1 file changed, 36 insertions(+), 12 deletions(-) > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > index 40ef5417d9545..d2ef535530b10 100644 > --- a/kernel/rcu/rcutorture.c > +++ b/kernel/rcu/rcutorture.c > @@ -1432,28 +1432,34 @@ static void rcutorture_one_extend(int *readstate, int newstate, > /* First, put new protection in place to avoid critical-section gap. */ > if (statesnew & RCUTORTURE_RDR_BH) > local_bh_disable(); > + if (statesnew & RCUTORTURE_RDR_RBH) > + rcu_read_lock_bh(); > if (statesnew & RCUTORTURE_RDR_IRQ) > local_irq_disable(); > if (statesnew & RCUTORTURE_RDR_PREEMPT) > preempt_disable(); > - if (statesnew & RCUTORTURE_RDR_RBH) > - rcu_read_lock_bh(); > if (statesnew & RCUTORTURE_RDR_SCHED) > rcu_read_lock_sched(); > if (statesnew & RCUTORTURE_RDR_RCU) > idxnew = cur_ops->readlock() << RCUTORTURE_RDR_SHIFT; > > - /* Next, remove old protection, irq first due to bh conflict. */ > + /* > + * Next, remove old protection, in decreasing order of strength > + * to avoid unlock paths that aren't safe in the stronger > + * context. Namely: BH can not be enabled with disabled interrupts. > + * Additionally PREEMPT_RT requires that BH is enabled in preemptible > + * context. > + */ > if (statesold & RCUTORTURE_RDR_IRQ) > local_irq_enable(); > - if (statesold & RCUTORTURE_RDR_BH) > - local_bh_enable(); > if (statesold & RCUTORTURE_RDR_PREEMPT) > preempt_enable(); > - if (statesold & RCUTORTURE_RDR_RBH) > - rcu_read_unlock_bh(); > if (statesold & RCUTORTURE_RDR_SCHED) > rcu_read_unlock_sched(); > + if (statesold & RCUTORTURE_RDR_BH) > + local_bh_enable(); > + if (statesold & RCUTORTURE_RDR_RBH) > + rcu_read_unlock_bh(); > if (statesold & RCUTORTURE_RDR_RCU) { > bool lockit = !statesnew && !(torture_random(trsp) & 0xffff); > > @@ -1496,6 +1502,9 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp) > int mask = rcutorture_extend_mask_max(); > unsigned long randmask1 = torture_random(trsp) >> 8; > unsigned long randmask2 = randmask1 >> 3; > + unsigned long preempts = RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED; > + unsigned long preempts_irq = preempts | RCUTORTURE_RDR_IRQ; > + unsigned long bhs = RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH; > > WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT); > /* Mostly only one bit (need preemption!), sometimes lots of bits. */ > @@ -1503,11 +1512,26 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp) > mask = mask & randmask2; > else > mask = mask & (1 << (randmask2 % RCUTORTURE_RDR_NBITS)); > - /* Can't enable bh w/irq disabled. */ > - if ((mask & RCUTORTURE_RDR_IRQ) && > - ((!(mask & RCUTORTURE_RDR_BH) && (oldmask & RCUTORTURE_RDR_BH)) || > - (!(mask & RCUTORTURE_RDR_RBH) && (oldmask & RCUTORTURE_RDR_RBH)))) > - mask |= RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH; > + > + /* > + * Can't enable bh w/irq disabled. > + */ > + if (mask & RCUTORTURE_RDR_IRQ) > + mask |= oldmask & bhs; > + > + /* > + * 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 modify BH in atomic context */ > + if (oldmask & preempts_irq) > + mask &= ~bhs; > + if ((oldmask | mask) & preempts_irq) > + mask |= oldmask & bhs; > + } > + > return mask ?: RCUTORTURE_RDR_RCU; > } > > -- > 2.33.0 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-08-20 22:10 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 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 [this message] 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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