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" <[email protected]> Cc: Steven Rostedt <[email protected]> Signed-off-by: Alexander Gordeev <[email protected]> --- 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 2fce662..8ce9c64 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++) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
