lkml.org 
[lkml]   [2020]   [Aug]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH tip/core/rcu 10/12] rcu: Provide optional RCU-reader exit delay for strict GPs
Date
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
\
 
 \ /
  Last update: 2020-08-13 00:58    [W:0.082 / U:2.812 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site