From: "tip-bot2 for Paul E. McKenney" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, x86 <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/entry] rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()
Date: Wed, 27 May 2020 08:12:02 -0000 [thread overview]
Message-ID: <159056712225.17951.7903035443251882028.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200521202116.996113173@linutronix.de>
The following commit has been merged into the x86/entry branch of tip:
Commit-ID: aaf2bc50df1f4bfc6857fc601fc7b21d5a18c6a1
Gitweb: https://git.kernel.org/tip/aaf2bc50df1f4bfc6857fc601fc7b21d5a18c6a1
Author: Paul E. McKenney <paulmck@kernel.org>
AuthorDate: Thu, 21 May 2020 22:05:15 +02:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 26 May 2020 19:04:18 +02:00
rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()
There will likely be exception handlers that can sleep, which rules
out the usual approach of invoking rcu_nmi_enter() on entry and also
rcu_nmi_exit() on all exit paths. However, the alternative approach of
just not calling anything can prevent RCU from coaxing quiescent states
from nohz_full CPUs that are looping in the kernel: RCU must instead
IPI them explicitly. It would be better to enable the scheduler tick
on such CPUs to interact with RCU in a lighter-weight manner, and this
enabling is one of the things that rcu_nmi_enter() currently does.
What is needed is something that helps RCU coax quiescent states while
not preventing subsequent sleeps. This commit therefore splits out the
nohz_full scheduler-tick enabling from the rest of the rcu_nmi_enter()
logic into a new function named rcu_irq_enter_check_tick().
[ tglx: Renamed the function and made it a nop when context tracking is off ]
[ mingo: Fixed a CONFIG_NO_HZ_FULL assumption, harmonized and fixed all the
comment blocks and cleaned up rcu_nmi_enter()/exit() definitions. ]
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200521202116.996113173@linutronix.de
---
include/linux/hardirq.h | 29 ++++++++------
kernel/rcu/tree.c | 82 ++++++++++++++++++++++++++++++----------
2 files changed, 79 insertions(+), 32 deletions(-)
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 621556e..e07cf85 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -2,31 +2,28 @@
#ifndef LINUX_HARDIRQ_H
#define LINUX_HARDIRQ_H
+#include <linux/context_tracking_state.h>
#include <linux/preempt.h>
#include <linux/lockdep.h>
#include <linux/ftrace_irq.h>
#include <linux/vtime.h>
#include <asm/hardirq.h>
-
extern void synchronize_irq(unsigned int irq);
extern bool synchronize_hardirq(unsigned int irq);
-#if defined(CONFIG_TINY_RCU)
-
-static inline void rcu_nmi_enter(void)
-{
-}
+#ifdef CONFIG_NO_HZ_FULL
+void __rcu_irq_enter_check_tick(void);
+#else
+static inline void __rcu_irq_enter_check_tick(void) { }
+#endif
-static inline void rcu_nmi_exit(void)
+static __always_inline void rcu_irq_enter_check_tick(void)
{
+ if (context_tracking_enabled())
+ __rcu_irq_enter_check_tick();
}
-#else
-extern void rcu_nmi_enter(void);
-extern void rcu_nmi_exit(void);
-#endif
-
/*
* It is safe to do non-atomic ops on ->hardirq_context,
* because NMI handlers may not preempt and the ops are
@@ -65,6 +62,14 @@ extern void irq_exit(void);
#define arch_nmi_exit() do { } while (0)
#endif
+#ifdef CONFIG_TINY_RCU
+static inline void rcu_nmi_enter(void) { }
+static inline void rcu_nmi_exit(void) { }
+#else
+extern void rcu_nmi_enter(void);
+extern void rcu_nmi_exit(void);
+#endif
+
/*
* NMI vs Tracing
* --------------
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 90c8be2..b7f8c49 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -848,6 +848,67 @@ void noinstr rcu_user_exit(void)
{
rcu_eqs_exit(1);
}
+
+/**
+ * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
+ *
+ * The scheduler tick is not normally enabled when CPUs enter the kernel
+ * from nohz_full userspace execution. After all, nohz_full userspace
+ * execution is an RCU quiescent state and the time executing in the kernel
+ * is quite short. Except of course when it isn't. And it is not hard to
+ * cause a large system to spend tens of seconds or even minutes looping
+ * in the kernel, which can cause a number of problems, include RCU CPU
+ * stall warnings.
+ *
+ * Therefore, if a nohz_full CPU fails to report a quiescent state
+ * in a timely manner, the RCU grace-period kthread sets that CPU's
+ * ->rcu_urgent_qs flag with the expectation that the next interrupt or
+ * exception will invoke this function, which will turn on the scheduler
+ * tick, which will enable RCU to detect that CPU's quiescent states,
+ * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
+ * The tick will be disabled once a quiescent state is reported for
+ * this CPU.
+ *
+ * Of course, in carefully tuned systems, there might never be an
+ * interrupt or exception. In that case, the RCU grace-period kthread
+ * will eventually cause one to happen. However, in less carefully
+ * controlled environments, this function allows RCU to get what it
+ * needs without creating otherwise useless interruptions.
+ */
+void __rcu_irq_enter_check_tick(void)
+{
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+ // Enabling the tick is unsafe in NMI handlers.
+ if (WARN_ON_ONCE(in_nmi()))
+ return;
+
+ RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
+ "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
+
+ if (!tick_nohz_full_cpu(rdp->cpu) ||
+ !READ_ONCE(rdp->rcu_urgent_qs) ||
+ READ_ONCE(rdp->rcu_forced_tick)) {
+ // RCU doesn't need nohz_full help from this CPU, or it is
+ // already getting that help.
+ return;
+ }
+
+ // We get here only when not in an extended quiescent state and
+ // from interrupts (as opposed to NMIs). Therefore, (1) RCU is
+ // already watching and (2) The fact that we are in an interrupt
+ // handler and that the rcu_node lock is an irq-disabled lock
+ // prevents self-deadlock. So we can safely recheck under the lock.
+ // Note that the nohz_full state currently cannot change.
+ raw_spin_lock_rcu_node(rdp->mynode);
+ if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
+ // A nohz_full CPU is in the kernel and RCU needs a
+ // quiescent state. Turn on the tick!
+ WRITE_ONCE(rdp->rcu_forced_tick, true);
+ tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
+ }
+ raw_spin_unlock_rcu_node(rdp->mynode);
+}
#endif /* CONFIG_NO_HZ_FULL */
/**
@@ -894,26 +955,7 @@ noinstr void rcu_nmi_enter(void)
incby = 1;
} else if (!in_nmi()) {
instrumentation_begin();
- if (tick_nohz_full_cpu(rdp->cpu) &&
- rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
- READ_ONCE(rdp->rcu_urgent_qs) &&
- !READ_ONCE(rdp->rcu_forced_tick)) {
- // We get here only if we had already exited the
- // extended quiescent state and this was an
- // interrupt (not an NMI). Therefore, (1) RCU is
- // already watching and (2) The fact that we are in
- // an interrupt handler and that the rcu_node lock
- // is an irq-disabled lock prevents self-deadlock.
- // So we can safely recheck under the lock.
- raw_spin_lock_rcu_node(rdp->mynode);
- if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
- // A nohz_full CPU is in the kernel and RCU
- // needs a quiescent state. Turn on the tick!
- WRITE_ONCE(rdp->rcu_forced_tick, true);
- tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
- }
- raw_spin_unlock_rcu_node(rdp->mynode);
- }
+ rcu_irq_enter_check_tick();
instrumentation_end();
}
instrumentation_begin();
next prev parent reply other threads:[~2020-05-27 8:12 UTC|newest]
Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-21 20:05 [patch V9 00/39] x86/entry: Rework leftovers (was part V) Thomas Gleixner
2020-05-21 20:05 ` [patch V9 01/39] nmi, tracing: Make hardware latency tracing noinstr safe Thomas Gleixner
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 02/39] rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter() Thomas Gleixner
2020-05-21 21:03 ` Paul E. McKenney
2020-05-21 21:25 ` Thomas Gleixner
2020-05-26 8:14 ` Ingo Molnar
2020-05-26 15:34 ` Paul E. McKenney
2020-05-27 8:12 ` tip-bot2 for Paul E. McKenney [this message]
2020-05-21 20:05 ` [patch V9 03/39] rcu: Provide rcu_irq_exit_check_preempt() Thomas Gleixner
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 04/39] x86/entry: Provide idtentry_entry/exit_cond_rcu() Thomas Gleixner
2020-05-21 21:06 ` Paul E. McKenney
2020-05-26 8:23 ` Ingo Molnar
2020-05-26 8:58 ` Thomas Gleixner
2020-05-21 20:05 ` [patch V9 05/39] x86/entry: Provide idtentry_enter/exit_user() Thomas Gleixner
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 06/39] x86/idtentry: Switch to conditional RCU handling Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 07/39] x86/entry: Cleanup idtentry_enter/exit() leftovers Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry: Clean up " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 08/39] genirq: Provide irq_enter/exit_rcu() Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 09/39] genirq: Provide __irq_enter/exit_raw() Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry: Provide helpers for executing on the irqstack tip-bot2 for Thomas Gleixner
2020-06-05 17:18 ` [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack Qian Cai
2020-06-05 17:36 ` Peter Zijlstra
2020-06-05 17:52 ` Qian Cai
2020-06-07 11:59 ` Thomas Gleixner
2020-06-07 18:27 ` Qian Cai
2020-06-08 16:01 ` Qian Cai
2020-06-08 22:20 ` Thomas Gleixner
2020-06-09 2:32 ` Qian Cai
2020-06-09 20:33 ` Thomas Gleixner
2020-06-09 20:50 ` Thomas Gleixner
2020-06-10 12:38 ` Qian Cai
2020-06-10 19:38 ` Thomas Gleixner
2020-06-13 13:55 ` Qian Cai
2020-06-13 14:03 ` Thomas Gleixner
2020-06-13 21:41 ` Qian Cai
2020-06-14 8:59 ` Thomas Gleixner
2020-05-21 20:05 ` [patch V9 11/39] x86/entry/64: Move do_softirq_own_stack() to C Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 12/39] x86/entry: Split out idtentry_exit_cond_resched() Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 13/39] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY Thomas Gleixner
2020-05-22 18:32 ` [patch V9-1 " Thomas Gleixner
2020-05-26 7:44 ` Jürgen Groß
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 14/39] x86/entry/64: Simplify idtentry_body Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 15/39] x86/entry: Switch page fault exception to IDTENTRY_RAW Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 16/39] x86/entry: Remove the transition leftovers Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 17/39] x86/entry: Change exit path of xen_failsafe_callback Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 18/39] x86/entry/64: Remove error_exit Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry/64: Remove error_exit() tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 19/39] x86/entry/32: Remove common_exception Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry/32: Remove common_exception() tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 20/39] x86/irq: Use generic irq_regs implementation Thomas Gleixner
2020-05-26 18:39 ` damian
2020-05-28 9:50 ` Thomas Gleixner
2020-05-28 20:20 ` damian
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 21/39] x86/irq: Convey vector as argument and not in ptregs Thomas Gleixner
2020-05-22 19:34 ` Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-08-24 17:29 ` [patch V9 21/39] " Alexander Graf
2020-08-25 10:28 ` Thomas Gleixner
2020-08-25 23:17 ` Alexander Graf
2020-08-25 23:41 ` Andy Lutomirski
2020-08-26 0:04 ` Alexander Graf
2020-08-26 1:03 ` Brian Gerst
2020-08-26 0:55 ` Thomas Gleixner
2020-05-21 20:05 ` [patch V9 22/39] x86/irq: Rework handle_irq() for 64bit Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/irq: Rework handle_irq() for 64-bit tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 23/39] x86/entry: Add IRQENTRY_IRQ macro Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 24/39] x86/entry: Use idtentry for interrupts Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 25/39] x86/entry: Provide IDTENTRY_SYSVEC Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 26/39] x86/entry: Convert APIC interrupts to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 27/39] x86/entry: Convert SMP system vectors " Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 28/39] x86/entry: Convert various system vectors Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 29/39] x86/entry: Convert KVM vectors to IDTENTRY_SYSVEC* Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 30/39] x86/entry: Convert various hypervisor vectors to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-26 9:29 ` Wei Liu
2020-05-27 1:46 ` Boqun Feng
2020-05-27 8:38 ` Wei Liu
2020-05-27 12:09 ` Wei Liu
2020-05-27 23:06 ` Boqun Feng
2020-05-27 12:30 ` Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 31/39] x86/entry: Convert XEN hypercall vector " Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 32/39] x86/entry: Convert reschedule interrupt to IDTENTRY_SYSVEC_SIMPLE Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 33/39] x86/entry: Remove the apic/BUILD interrupt leftovers Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 34/39] x86/entry/64: Remove IRQ stack switching ASM Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 35/39] x86/entry: Make enter_from_user_mode() static Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 36/39] x86/entry/32: Remove redundant irq disable code Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 37/39] x86/entry/64: Remove TRACE_IRQS_*_DEBUG Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 38/39] x86/entry: Move paranoid irq tracing out of ASM code Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 39/39] x86/entry: Remove the TRACE_IRQS cruft Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-22 7:20 ` [patch V9 00/39] x86/entry: Rework leftovers (was part V) Andrew Cooper
2020-05-22 21:17 ` Peter Zijlstra
2020-06-03 19:18 ` Andrew Cooper
2020-06-04 13:25 ` Peter Zijlstra
2020-06-04 13:29 ` Paolo Bonzini
2020-06-04 13:35 ` Peter Zijlstra
2020-06-04 15:42 ` Andy Lutomirski
2020-06-04 15:55 ` Peter Zijlstra
2020-05-22 14:26 ` Boris Ostrovsky
2020-05-22 17:47 ` Thomas Gleixner
2020-05-22 18:08 ` Thomas Gleixner
2020-05-26 4:33 ` Andy Lutomirski
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