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Subject[PATCH tip/core/rcu 04/12] rcu: Force DEFAULT_RCU_BLIMIT to 1000 for strict RCU GPs
Date
From: "Paul E. McKenney" <paulmck@kernel.org>

The value of DEFAULT_RCU_BLIMIT is normally set to 10, the idea being to
avoid needless response-time degradation due to RCU callback invocation.
However, when CONFIG_RCU_STRICT_GRACE_PERIOD=y it is better to avoid
throttling callback execution in order to better detect pointer
leaks from RCU read-side critical sections. This commit therefore
sets the value of DEFAULT_RCU_BLIMIT to 1000 in kernels built with
CONFIG_RCU_STRICT_GRACE_PERIOD=y.

Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d333f1b..08cc91c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -454,17 +454,18 @@ static int rcu_is_cpu_rrupt_from_idle(void)
return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
}

-#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch ... */
-#define DEFAULT_MAX_RCU_BLIMIT 10000 /* ... even during callback flood. */
+#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
+ // Maximum callbacks per rcu_do_batch ...
+#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
static long blimit = DEFAULT_RCU_BLIMIT;
-#define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
+#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
static long qhimark = DEFAULT_RCU_QHIMARK;
-#define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
+#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
static long qlowmark = DEFAULT_RCU_QLOMARK;
#define DEFAULT_RCU_QOVLD_MULT 2
#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
-static long qovld = DEFAULT_RCU_QOVLD; /* If this many pending, hammer QS. */
-static long qovld_calc = -1; /* No pre-initialization lock acquisitions! */
+static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
+static long qovld_calc = -1; // No pre-initialization lock acquisitions!

module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
--
2.9.5
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