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Subject[PATCH v2 1/9] rcu: Panic if RCU tree can not accommodate all CPUs
Date
Currently a condition when RCU tree is unable to accommodate
the configured number of CPUs is not permitted and causes
a fall back to compile-time values. However, the code has no
means to exceed the RCU tree capacity neither at compile-time
nor in run-time. Therefore, if the condition is met in run-
time then it indicates a serios problem elsewhere and should
be handled with a panic.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
---
kernel/rcu/tree.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2fce662..66a4230 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4117,16 +4117,19 @@ static void __init rcu_init_geometry(void)
rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;

/*
+ * The tree must be able to accommodate the configured number of CPUs.
+ * If this limit is exceeded than we have a serious problem elsewhere.
+ *
* The boot-time rcu_fanout_leaf parameter is only permitted
* to increase the leaf-level fanout, not decrease it. Of course,
* the leaf-level fanout cannot exceed the number of bits in
- * the rcu_node masks. Finally, the tree must be able to accommodate
- * the configured number of CPUs. Complain and fall back to the
- * compile-time values if these limits are exceeded.
+ * the rcu_node masks. Complain and fall back to the compile-
+ * time values if these limits are exceeded.
*/
- if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
- rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
- n > rcu_capacity[MAX_RCU_LVLS]) {
+ if (n > rcu_capacity[MAX_RCU_LVLS])
+ panic("rcu_init_geometry: rcu_capacity[] is too small");
+ else if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
+ rcu_fanout_leaf > sizeof(unsigned long) * 8) {
WARN_ON(1);
return;
}
--
1.8.3.1


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