From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
elver@google.com, dvyukov@google.com,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 10/12] rcu: Provide optional RCU-reader exit delay for strict GPs
Date: Wed, 12 Aug 2020 15:57:30 -0700 [thread overview]
Message-ID: <20200812225732.20068-10-paulmck@kernel.org> (raw)
In-Reply-To: <20200812225632.GA19759@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
The goal of this series is to increase the probability of tools like
KASAN detecting that an RCU-protected pointer was used outside of its
RCU read-side critical section. Thus far, the approach has been to make
grace periods and callback processing happen faster. Another approach
is to delay the pointer leaker. This commit therefore allows a delay
to be applied to exit from RCU read-side critical sections.
This slowdown is specified by a new rcutree.rcu_unlock_delay kernel boot
parameter that specifies this delay in microseconds, defaulting to zero.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
kernel/rcu/tree_plugin.h | 12 ++++++++++--
2 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 60e2c6e..c532c70 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4128,6 +4128,15 @@
This wake_up() will be accompanied by a
WARN_ONCE() splat and an ftrace_dump().
+ rcutree.rcu_unlock_delay= [KNL]
+ In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
+ this specifies an rcu_read_unlock()-time delay
+ in microseconds. This defaults to zero.
+ Larger delays increase the probability of
+ catching RCU pointer leaks, that is, buggy use
+ of RCU-protected pointers after the relevant
+ rcu_read_unlock() has completed.
+
rcutree.sysrq_rcu= [KNL]
Commandeer a sysrq key to dump out Tree RCU's
rcu_node tree with an eye towards determining
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1761ff4..25c9ee4 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -430,6 +430,12 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
return !list_empty(&rnp->blkd_tasks);
}
+// Add delay to rcu_read_unlock() for strict grace periods.
+static int rcu_unlock_delay;
+#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
+module_param(rcu_unlock_delay, int, 0444);
+#endif
+
/*
* Report deferred quiescent states. The deferral time can
* be quite short, for example, in the case of the call from
@@ -460,10 +466,12 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
}
t->rcu_read_unlock_special.s = 0;
if (special.b.need_qs) {
- if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
rcu_report_qs_rdp(rdp->cpu, rdp);
- else
+ udelay(rcu_unlock_delay);
+ } else {
rcu_qs();
+ }
}
/*
--
2.9.5
next prev parent reply other threads:[~2020-08-12 22:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 22:56 [PATCH tip/core/rcu 0/12] Add strict short-grace-period Kconfig option Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 01/12] rcu: Add Kconfig option for strict RCU grace periods paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 02/12] rcu: Reduce leaf fanout " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 03/12] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 04/12] rcu: Force DEFAULT_RCU_BLIMIT to 1000 " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 05/12] rcu: Always set .need_qs from __rcu_read_lock() for strict GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 06/12] rcu: Do full report for .need_qs " paulmck
2020-08-13 0:50 ` Jann Horn
2020-08-13 3:29 ` Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 07/12] rcu: Attempt QS when CPU discovers GP " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 08/12] rcu: IPI all CPUs at GP start " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 09/12] rcu: IPI all CPUs at GP end " paulmck
2020-08-12 22:57 ` paulmck [this message]
2020-08-12 22:57 ` [PATCH tip/core/rcu 11/12] rcu: Execute RCU reader shortly after rcu_core " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 12/12] rcu: Report QS for outermost PREEMPT=n rcu_read_unlock() " paulmck
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