121 lines
4.2 KiB
Diff
121 lines
4.2 KiB
Diff
From d8013f2182d632f63ac3aa45d37a9a1f2806037a Mon Sep 17 00:00:00 2001
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Message-Id: <d8013f2182d632f63ac3aa45d37a9a1f2806037a.1601675152.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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Date: Wed, 5 Oct 2011 11:45:18 -0700
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Subject: [PATCH 159/333] rcu: Make ksoftirqd do RCU quiescent states
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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Implementing RCU-bh in terms of RCU-preempt makes the system vulnerable
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to network-based denial-of-service attacks. This patch therefore
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makes __do_softirq() invoke rcu_bh_qs(), but only when __do_softirq()
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is running in ksoftirqd context. A wrapper layer in interposed so that
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other calls to __do_softirq() avoid invoking rcu_bh_qs(). The underlying
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function __do_softirq_common() does the actual work.
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The reason that rcu_bh_qs() is bad in these non-ksoftirqd contexts is
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that there might be a local_bh_enable() inside an RCU-preempt read-side
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critical section. This local_bh_enable() can invoke __do_softirq()
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directly, so if __do_softirq() were to invoke rcu_bh_qs() (which just
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calls rcu_preempt_qs() in the PREEMPT_RT_FULL case), there would be
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an illegal RCU-preempt quiescent state in the middle of an RCU-preempt
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read-side critical section. Therefore, quiescent states can only happen
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in cases where __do_softirq() is invoked directly from ksoftirqd.
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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Link: http://lkml.kernel.org/r/20111005184518.GA21601@linux.vnet.ibm.com
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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kernel/rcu/tree.c | 18 +++++++++++++-----
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kernel/rcu/tree_plugin.h | 8 +++++++-
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2 files changed, 20 insertions(+), 6 deletions(-)
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diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
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index 1456a3d97971..1a40e3d44cb8 100644
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--- a/kernel/rcu/tree.c
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+++ b/kernel/rcu/tree.c
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@@ -244,7 +244,19 @@ void rcu_sched_qs(void)
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this_cpu_ptr(&rcu_sched_data), true);
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}
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-#ifndef CONFIG_PREEMPT_RT_FULL
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+static void rcu_preempt_qs(void);
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+
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+void rcu_bh_qs(void)
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+{
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+ unsigned long flags;
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+
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+ /* Callers to this function, rcu_preempt_qs(), must disable irqs. */
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+ local_irq_save(flags);
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+ rcu_preempt_qs();
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+ local_irq_restore(flags);
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+}
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+#else
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void rcu_bh_qs(void)
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{
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RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!");
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@@ -255,10 +267,6 @@ void rcu_bh_qs(void)
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__this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
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}
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}
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-#else
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-void rcu_bh_qs(void)
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-{
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-}
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#endif
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/*
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diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
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index e9ce51e19e87..938e64c69d18 100644
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--- a/kernel/rcu/tree_plugin.h
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+++ b/kernel/rcu/tree_plugin.h
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@@ -29,6 +29,7 @@
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#include <linux/oom.h>
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#include <linux/sched/debug.h>
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#include <linux/smpboot.h>
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+#include <linux/jiffies.h>
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#include <linux/sched/isolation.h>
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#include <uapi/linux/sched/types.h>
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#include "../time/tick-internal.h"
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@@ -1408,7 +1409,7 @@ static void rcu_prepare_kthreads(int cpu)
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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-#if !defined(CONFIG_RCU_FAST_NO_HZ)
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+#if !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL)
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/*
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* Check to see if any future RCU-related work will need to be done
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@@ -1424,7 +1425,9 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
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*nextevt = KTIME_MAX;
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return rcu_cpu_has_callbacks(NULL);
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}
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+#endif /* !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) */
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+#if !defined(CONFIG_RCU_FAST_NO_HZ)
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/*
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* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
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* after it.
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@@ -1521,6 +1524,8 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void)
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return cbs_ready;
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}
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+#ifndef CONFIG_PREEMPT_RT_FULL
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+
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/*
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* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
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* to invoke. If the CPU has callbacks, try to advance them. Tell the
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@@ -1563,6 +1568,7 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
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*nextevt = basemono + dj * TICK_NSEC;
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return 0;
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}
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+#endif /* #ifndef CONFIG_PREEMPT_RT_FULL */
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/*
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* Prepare a CPU for idle from an RCU perspective. The first major task
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--
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2.17.1
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