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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Marc Zyngier <maz@kernel.org>, Rich Felker <dalias@libc.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Paul McKenney <paulmck@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	linux-sh@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Richard Weinberger <richard@nod.at>,
	Frederic Weisbecker <frederic@kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Jeff Dike <jdike@addtoit.com>,
	Russell King <linux@armlinux.org.uk>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	linux-parisc@vger.kernel.org, Helge Deller <deller@gmx.de>,
	linux-um@lists.infradead.org, Will Deacon <will@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>
Subject: [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT
Date: Fri, 13 Nov 2020 14:02:26 +0000	[thread overview]
Message-ID: <20201113141734.907075915@linutronix.de> (raw)
In-Reply-To: <20201113140207.499353218@linutronix.de>

tasklet_kill() and tasklet_unlock_wait() spin and wait for the
TASKLET_STATE_SCHED resp. TASKLET_STATE_RUN bit in the tasklet state to be
cleared. This works on !RT nicely because the corresponding execution can
only happen on a different CPU.

On RT softirq processing is preemptible, therefore a task preempting the
softirq processing thread can spin forever. Prevent this by invoking
local_bh_disable()/enable() inside the loop. In case that the softirq
processing thread was preempted by the current task, current will block on
the local lock which yields the CPU to the preempted softirq processing
thread. If the tasklet is processed on a different CPU then the
local_bh_disable()/enable() pair is just a waste of processor cycles.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/interrupt.h |    8 ++------
 kernel/softirq.c          |   38 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 7 deletions(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -654,7 +654,7 @@ enum
 	TASKLET_STATE_RUN	/* Tasklet is running (SMP only) */
 };
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 static inline int tasklet_trylock(struct tasklet_struct *t)
 {
 	return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state);
@@ -666,11 +666,7 @@ static inline void tasklet_unlock(struct
 	clear_bit(TASKLET_STATE_RUN, &(t)->state);
 }
 
-static inline void tasklet_unlock_wait(struct tasklet_struct *t)
-{
-	while (test_bit(TASKLET_STATE_RUN, &(t)->state))
-		cpu_relax();
-}
+void tasklet_unlock_wait(struct tasklet_struct *t);
 #else
 static inline int tasklet_trylock(struct tasklet_struct *t) { return 1; }
 static inline void tasklet_unlock(struct tasklet_struct *t) { }
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -851,6 +851,29 @@ void tasklet_init(struct tasklet_struct
 }
 EXPORT_SYMBOL(tasklet_init);
 
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
+
+void tasklet_unlock_wait(struct tasklet_struct *t)
+{
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			/*
+			 * Prevent a live lock when current preempted soft
+			 * interrupt processing or prevents ksoftirqd from
+			 * running. If the tasklet runs on a different CPU
+			 * then this has no effect other than doing the BH
+			 * disable/enable dance for nothing.
+			 */
+			local_bh_disable();
+			local_bh_enable();
+		} else {
+			cpu_relax();
+		}
+	}
+}
+EXPORT_SYMBOL(tasklet_unlock_wait);
+#endif
+
 void tasklet_kill(struct tasklet_struct *t)
 {
 	if (in_interrupt())
@@ -858,7 +881,20 @@ void tasklet_kill(struct tasklet_struct
 
 	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 		do {
-			yield();
+			if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+				/*
+				 * Prevent a live lock when current
+				 * preempted soft interrupt processing or
+				 * prevents ksoftirqd from running. If the
+				 * tasklet runs on a different CPU then
+				 * this has no effect other than doing the
+				 * BH disable/enable dance for nothing.
+				 */
+				local_bh_disable();
+				local_bh_enable();
+			} else {
+				yield();
+			}
 		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
 	}
 	tasklet_unlock_wait(t);

WARNING: multiple messages have this Message-ID
From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Paul McKenney <paulmck@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Arnd Bergmann <arnd@arndb.de>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	Helge Deller <deller@gmx.de>,
	linux-parisc@vger.kernel.org,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	linux-sh@vger.kernel.org, Jeff Dike <jdike@addtoit.com>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	linux-um@lists.infradead.org,
	Russell King <linux@armlinux.org.uk>,
	Marc Zyngier <maz@kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Subject: [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT
Date: Fri, 13 Nov 2020 15:02:26 +0100	[thread overview]
Message-ID: <20201113141734.907075915@linutronix.de> (raw)
In-Reply-To: <20201113140207.499353218@linutronix.de>

tasklet_kill() and tasklet_unlock_wait() spin and wait for the
TASKLET_STATE_SCHED resp. TASKLET_STATE_RUN bit in the tasklet state to be
cleared. This works on !RT nicely because the corresponding execution can
only happen on a different CPU.

On RT softirq processing is preemptible, therefore a task preempting the
softirq processing thread can spin forever. Prevent this by invoking
local_bh_disable()/enable() inside the loop. In case that the softirq
processing thread was preempted by the current task, current will block on
the local lock which yields the CPU to the preempted softirq processing
thread. If the tasklet is processed on a different CPU then the
local_bh_disable()/enable() pair is just a waste of processor cycles.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/interrupt.h |    8 ++------
 kernel/softirq.c          |   38 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 7 deletions(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -654,7 +654,7 @@ enum
 	TASKLET_STATE_RUN	/* Tasklet is running (SMP only) */
 };
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 static inline int tasklet_trylock(struct tasklet_struct *t)
 {
 	return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state);
@@ -666,11 +666,7 @@ static inline void tasklet_unlock(struct
 	clear_bit(TASKLET_STATE_RUN, &(t)->state);
 }
 
-static inline void tasklet_unlock_wait(struct tasklet_struct *t)
-{
-	while (test_bit(TASKLET_STATE_RUN, &(t)->state))
-		cpu_relax();
-}
+void tasklet_unlock_wait(struct tasklet_struct *t);
 #else
 static inline int tasklet_trylock(struct tasklet_struct *t) { return 1; }
 static inline void tasklet_unlock(struct tasklet_struct *t) { }
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -851,6 +851,29 @@ void tasklet_init(struct tasklet_struct
 }
 EXPORT_SYMBOL(tasklet_init);
 
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
+
+void tasklet_unlock_wait(struct tasklet_struct *t)
+{
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			/*
+			 * Prevent a live lock when current preempted soft
+			 * interrupt processing or prevents ksoftirqd from
+			 * running. If the tasklet runs on a different CPU
+			 * then this has no effect other than doing the BH
+			 * disable/enable dance for nothing.
+			 */
+			local_bh_disable();
+			local_bh_enable();
+		} else {
+			cpu_relax();
+		}
+	}
+}
+EXPORT_SYMBOL(tasklet_unlock_wait);
+#endif
+
 void tasklet_kill(struct tasklet_struct *t)
 {
 	if (in_interrupt())
@@ -858,7 +881,20 @@ void tasklet_kill(struct tasklet_struct
 
 	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 		do {
-			yield();
+			if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+				/*
+				 * Prevent a live lock when current
+				 * preempted soft interrupt processing or
+				 * prevents ksoftirqd from running. If the
+				 * tasklet runs on a different CPU then
+				 * this has no effect other than doing the
+				 * BH disable/enable dance for nothing.
+				 */
+				local_bh_disable();
+				local_bh_enable();
+			} else {
+				yield();
+			}
 		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
 	}
 	tasklet_unlock_wait(t);


WARNING: multiple messages have this Message-ID
From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Marc Zyngier <maz@kernel.org>, Rich Felker <dalias@libc.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Paul McKenney <paulmck@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	linux-sh@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Richard Weinberger <richard@nod.at>,
	Frederic Weisbecker <frederic@kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Jeff Dike <jdike@addtoit.com>,
	Russell King <linux@armlinux.org.uk>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	linux-parisc@vger.kernel.org, Helge Deller <deller@gmx.de>,
	linux-um@lists.infradead.org, Will Deacon <will@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	linux-arm-kernel@lists.infradead.org,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>
Subject: [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT
Date: Fri, 13 Nov 2020 15:02:26 +0100	[thread overview]
Message-ID: <20201113141734.907075915@linutronix.de> (raw)
In-Reply-To: <20201113140207.499353218@linutronix.de>

tasklet_kill() and tasklet_unlock_wait() spin and wait for the
TASKLET_STATE_SCHED resp. TASKLET_STATE_RUN bit in the tasklet state to be
cleared. This works on !RT nicely because the corresponding execution can
only happen on a different CPU.

On RT softirq processing is preemptible, therefore a task preempting the
softirq processing thread can spin forever. Prevent this by invoking
local_bh_disable()/enable() inside the loop. In case that the softirq
processing thread was preempted by the current task, current will block on
the local lock which yields the CPU to the preempted softirq processing
thread. If the tasklet is processed on a different CPU then the
local_bh_disable()/enable() pair is just a waste of processor cycles.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/interrupt.h |    8 ++------
 kernel/softirq.c          |   38 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 7 deletions(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -654,7 +654,7 @@ enum
 	TASKLET_STATE_RUN	/* Tasklet is running (SMP only) */
 };
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
 static inline int tasklet_trylock(struct tasklet_struct *t)
 {
 	return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state);
@@ -666,11 +666,7 @@ static inline void tasklet_unlock(struct
 	clear_bit(TASKLET_STATE_RUN, &(t)->state);
 }
 
-static inline void tasklet_unlock_wait(struct tasklet_struct *t)
-{
-	while (test_bit(TASKLET_STATE_RUN, &(t)->state))
-		cpu_relax();
-}
+void tasklet_unlock_wait(struct tasklet_struct *t);
 #else
 static inline int tasklet_trylock(struct tasklet_struct *t) { return 1; }
 static inline void tasklet_unlock(struct tasklet_struct *t) { }
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -851,6 +851,29 @@ void tasklet_init(struct tasklet_struct
 }
 EXPORT_SYMBOL(tasklet_init);
 
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
+
+void tasklet_unlock_wait(struct tasklet_struct *t)
+{
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			/*
+			 * Prevent a live lock when current preempted soft
+			 * interrupt processing or prevents ksoftirqd from
+			 * running. If the tasklet runs on a different CPU
+			 * then this has no effect other than doing the BH
+			 * disable/enable dance for nothing.
+			 */
+			local_bh_disable();
+			local_bh_enable();
+		} else {
+			cpu_relax();
+		}
+	}
+}
+EXPORT_SYMBOL(tasklet_unlock_wait);
+#endif
+
 void tasklet_kill(struct tasklet_struct *t)
 {
 	if (in_interrupt())
@@ -858,7 +881,20 @@ void tasklet_kill(struct tasklet_struct
 
 	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
 		do {
-			yield();
+			if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+				/*
+				 * Prevent a live lock when current
+				 * preempted soft interrupt processing or
+				 * prevents ksoftirqd from running. If the
+				 * tasklet runs on a different CPU then
+				 * this has no effect other than doing the
+				 * BH disable/enable dance for nothing.
+				 */
+				local_bh_disable();
+				local_bh_enable();
+			} else {
+				yield();
+			}
 		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
 	}
 	tasklet_unlock_wait(t);


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  parent reply	other threads:[~2020-11-13 14:02 UTC|newest]

Thread overview: 115+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-13 14:02 [patch 00/19] softirq: Cleanups and RT awareness Thomas Gleixner
2020-11-13 14:02 ` Thomas Gleixner
2020-11-13 14:02 ` Thomas Gleixner
2020-11-13 14:02 ` [patch 01/19] parisc: Remove bogus __IRQ_STAT macro Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 02/19] sh: Get rid of nmi_count() Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2021-01-01 14:27   ` [patch 02/19] " John Paul Adrian Glaubitz
2021-01-01 14:27     ` John Paul Adrian Glaubitz
2020-11-13 14:02 ` [patch 03/19] irqstat: Get rid of nmi_count() and __IRQ_STAT() Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 04/19] um/irqstat: Get rid of the duplicated declarations Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 05/19] ARM: irqstat: Get rid of duplicated declaration Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-16 18:19   ` Valentin Schneider
2020-11-16 18:19     ` Valentin Schneider
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 06/19] arm64: " Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-16 10:01   ` Will Deacon
2020-11-16 10:01     ` Will Deacon
2020-11-16 10:01     ` Will Deacon
2020-11-16 10:51   ` Marc Zyngier
2020-11-16 10:51     ` Marc Zyngier
2020-11-16 10:51     ` Marc Zyngier
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 07/19] asm-generic/irqstat: Add optional __nmi_count member Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 08/19] sh: irqstat: Use the generic irq_cpustat_t Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 09/19] irqstat: Move declaration into asm-generic/hardirq.h Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 10/19] preempt: Cleanup the macro maze a bit Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-16 12:17   ` Peter Zijlstra
2020-11-16 12:17     ` Peter Zijlstra
2020-11-16 12:17     ` Peter Zijlstra
2020-11-16 17:42     ` Thomas Gleixner
2020-11-16 17:42       ` Thomas Gleixner
2020-11-16 17:42       ` Thomas Gleixner
2020-11-17 10:21       ` Peter Zijlstra
2020-11-17 10:21         ` Peter Zijlstra
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 11/19] softirq: Move related code into one section Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-19 12:20   ` Frederic Weisbecker
2020-11-19 12:20     ` Frederic Weisbecker
2020-11-23 22:51   ` [tip: irq/core] " tip-bot2 for Thomas Gleixner
2020-11-13 14:02 ` [patch 12/19] softirq: Add RT specific softirq accounting Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-19 12:18   ` Frederic Weisbecker
2020-11-19 12:18     ` Frederic Weisbecker
2020-11-19 18:34     ` Thomas Gleixner
2020-11-19 18:34       ` Thomas Gleixner
2020-11-19 22:52       ` Frederic Weisbecker
2020-11-19 22:52         ` Frederic Weisbecker
2020-11-13 14:02 ` [patch 13/19] softirq: Move various protections into inline helpers Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 14/19] softirq: Make softirq control and processing RT aware Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-20  0:26   ` Frederic Weisbecker
2020-11-20  0:26     ` Frederic Weisbecker
2020-11-20 13:27     ` Thomas Gleixner
2020-11-20 13:27       ` Thomas Gleixner
2020-11-23 13:44   ` Frederic Weisbecker
2020-11-23 13:44     ` Frederic Weisbecker
2020-11-23 19:27     ` Thomas Gleixner
2020-11-23 19:27       ` Thomas Gleixner
2020-11-23 19:56       ` Frederic Weisbecker
2020-11-23 19:56         ` Frederic Weisbecker
2020-11-23 23:58       ` Frederic Weisbecker
2020-11-23 23:58         ` Frederic Weisbecker
2020-11-24  0:06         ` Thomas Gleixner
2020-11-24  0:06           ` Thomas Gleixner
2020-11-24  0:13           ` Frederic Weisbecker
2020-11-24  0:13             ` Frederic Weisbecker
2020-11-24  0:22             ` Thomas Gleixner
2020-11-24  0:22               ` Thomas Gleixner
2020-11-13 14:02 ` [patch 15/19] tick/sched: Prevent false positive softirq pending warnings on RT Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 16/19] rcu: Prevent false positive softirq warning " Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 17/19] softirq: Replace barrier() with cpu_relax() in tasklet_unlock_wait() Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` [patch 18/19] tasklets: Use static inlines for stub implementations Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner
2020-11-13 14:02 ` Thomas Gleixner [this message]
2020-11-13 14:02   ` [patch 19/19] tasklets: Prevent kill/unlock_wait deadlock on RT Thomas Gleixner
2020-11-13 14:02   ` Thomas Gleixner

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