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rcu: Panic if RCU tree can not accommodate all CPUs

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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>
This commit is contained in:
Alexander Gordeev 2015-06-03 08:18:23 +02:00 committed by Paul E. McKenney
parent 319362c90f
commit 75cf15a4c0
1 changed files with 17 additions and 12 deletions
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29
kernel/rcu/tree.c
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@ -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", pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
rcu_fanout_leaf, nr_cpu_ids); 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 * Compute number of nodes that can be handled an rcu_node tree
* with the given number of levels. Setting rcu_capacity[0] makes * 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; rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
/* /*
* The boot-time rcu_fanout_leaf parameter is only permitted * The tree must be able to accommodate the configured number of CPUs.
* to increase the leaf-level fanout, not decrease it. Of course, * If this limit is exceeded than we have a serious problem elsewhere.
* 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.
*/ */
if (rcu_fanout_leaf < RCU_FANOUT_LEAF || if (n > rcu_capacity[MAX_RCU_LVLS])
rcu_fanout_leaf > sizeof(unsigned long) * 8 || panic("rcu_init_geometry: rcu_capacity[] is too small");
n > rcu_capacity[MAX_RCU_LVLS]) {
WARN_ON(1);
return;
}
/* Calculate the number of rcu_nodes at each level of the tree. */ /* Calculate the number of rcu_nodes at each level of the tree. */
for (i = 1; i <= MAX_RCU_LVLS; i++) for (i = 1; i <= MAX_RCU_LVLS; i++)