Messages in this thread | | | Date | Sat, 7 Mar 2015 09:42:34 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/9] rcu: Panic if RCU tree can not accommodate all CPUs |
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On Sat, Mar 07, 2015 at 06:03:36PM +0100, Alexander Gordeev wrote: > 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> > Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
The place to put a check like this is in the code that calculates nr_cpu_ids. And at least some (perhaps all) are set up so that nr_cpu_ids cannot exceed NR_CPUS, which would render this check redundant.
So I have to say "no" to this one.
Thanx, Paul
> --- > kernel/rcu/tree.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 48d640c..7588c7f 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3889,16 +3889,19 @@ static void __init rcu_init_geometry(void) > rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT; > > /* > + * The tree must be able to accommodate the configured number of CPUs. > + * If this limit is exceeded than we have a serious problem elsewhere. > + * > * 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 rcu_node masks. Complain and fall back to the compile- > + * time values if these limits are exceeded. > */ > - if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF || > - rcu_fanout_leaf > sizeof(unsigned long) * 8 || > - n > rcu_capacity[MAX_RCU_LVLS]) { > + if (n > rcu_capacity[MAX_RCU_LVLS]) > + panic("rcu_init_geometry: rcu_capacity[] is too small"); > + else if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF || > + rcu_fanout_leaf > sizeof(unsigned long) * 8) { > WARN_ON(1); > return; > } > -- > 1.8.3.1 >
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