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| author |   Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-31 08:28:35 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-10-06 11:09:41 -0700 |
| commit | ee968ac61d5a3440b931375d81113e0eedfcb249 (patch) | |
| tree | ac6f4bc6727b19506941412b6d09c5fe44ca8b3d /kernel/rcu | |
| parent | rcu: Don't disable preemption for Tiny and Tree RCU readers (diff) | |
| download | linux-dev-ee968ac61d5a3440b931375d81113e0eedfcb249.tar.xz linux-dev-ee968ac61d5a3440b931375d81113e0eedfcb249.zip | |
rcu: Eliminate panic when silly boot-time fanout specified
This commit loosens rcutree.rcu_fanout_leaf range checks
and replaces a panic() with a fallback to compile-time values.
This fallback is accompanied by a WARN_ON(), and both occur when the
rcutree.rcu_fanout_leaf value is too small to accommodate the number of
CPUs. For example, given the current four-level limit for the rcu_node
tree, a system with more than 16 CPUs built with CONFIG_FANOUT=2 must
have rcutree.rcu_fanout_leaf larger than 2.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 93c0f23c3e45..713eb92314b4 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4230,13 +4230,12 @@ 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. + * The boot-time rcu_fanout_leaf parameter must be at least two + * and cannot exceed the number of bits in the rcu_node masks. + * Complain and fall back to the compile-time values if this + * limit is exceeded. */ - if (rcu_fanout_leaf < RCU_FANOUT_LEAF || + if (rcu_fanout_leaf < 2 || rcu_fanout_leaf > sizeof(unsigned long) * 8) { rcu_fanout_leaf = RCU_FANOUT_LEAF; WARN_ON(1); @@ -4253,10 +4252,13 @@ static void __init rcu_init_geometry(void) /* * 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 this limit is exceeded, fall back to the compile-time values. */ - if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) - panic("rcu_init_geometry: rcu_capacity[] is too small"); + if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) { + rcu_fanout_leaf = RCU_FANOUT_LEAF; + WARN_ON(1); + return; + } /* Calculate the number of levels in the tree. */ for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) { |