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Commit 75cf15a4 authored by Alexander Gordeev's avatar Alexander Gordeev Committed by Paul E. McKenney
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rcu: Panic if RCU tree can not accommodate all CPUs 



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: default avatarAlexander Gordeev <agordeev@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 319362c9

kernel/rcu/tree.c

+17 −12
Original line number Diff line number Diff line
@@ -4106,6 +4106,19 @@ static void __init rcu_init_geometry(void) 
	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",

		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
@@ -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++)