Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1187264

[PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs

Show all headers | View raw

From: Alexander Gordeev <agordeev@redhat.com>

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>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1c58cbd03922..fe8d92987dfa 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4107,6 +4107,19 @@ static void __init rcu_init_geometry(void)
 		rcu_fanout_leaf, nr_cpu_ids);
 
 	/*
+	 * 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.  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) {
+		WARN_ON(1);
+		return;
+	}
+
+	/*
 	 * Compute number of nodes that can be handled an rcu_node tree
 	 * with the given number of levels.  Setting rcu_capacity[0] makes
 	 * some of the arithmetic easier.
@@ -4117,19 +4130,11 @@ static void __init rcu_init_geometry(void)
 		rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
 
 	/*
-	 * 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 tree must be able to accommodate the configured number of CPUs.
+	 * If this limit is exceeded than we have a serious problem elsewhere.
 	 */
-	if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
-	    rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
-	    n > rcu_capacity[MAX_RCU_LVLS]) {
-		WARN_ON(1);
-		return;
-	}
+	if (n > rcu_capacity[MAX_RCU_LVLS])
+		panic("rcu_init_geometry: rcu_capacity[] is too small");
 
 	/* Calculate the number of rcu_nodes at each level of the tree. */
 	for (i = 1; i <= MAX_RCU_LVLS; i++)
-- 
1.8.1.5

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH tip/core/rcu 0/12] Tree geometry-initialization  simplifications for 4.3 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 03/12] rcu: Remove superfluous local variable in rcu_init_geometry() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 08/12] rcu: Remove unnecessary fields from rcu_state structure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 12/12] rcu: Reset rcu_fanout_leaf if out of bounds "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 11/12] rcu: Shut up bogus gcc array bounds warning "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 10/12] rcu: Simplify arithmetic to calculate number of RCU nodes "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 05/12] rcu: Simplify rcu_init_geometry() capacity arithmetics "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 09/12] rcu: Limit count of static data to the number of RCU levels "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 01/12] rcu: Provide more diagnostics for stalled GP kthread "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 04/12] rcu: Cleanup rcu_init_geometry() code and arithmetics "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 07/12] rcu: Limit rcu_capacity[] size to RCU_NUM_LVLS items "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 06/12] rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200

csiph-web