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rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_divisor 

Given that sysfs can change the value of rcu_divisor at any time, this
commit adds a READ_ONCE to the sole access to that variable.  While in
the area, this commit also adds bounds checking, clamping the value to
a shift that makes sense for a signed long.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-06-23 17:09:27 -07:00
parent 2130c6b4f6
commit b5374b2df0
1 changed files with 4 additions and 1 deletions
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5
kernel/rcu/tree.c
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@ -2362,6 +2362,7 @@ int rcutree_dead_cpu(unsigned int cpu)
*/
static void rcu_do_batch(struct rcu_data *rdp)
{
int div;
unsigned long flags;
const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
rcu_segcblist_is_offloaded(&rdp->cblist);
@ -2390,7 +2391,9 @@ static void rcu_do_batch(struct rcu_data *rdp)
rcu_nocb_lock(rdp);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
pending = rcu_segcblist_n_cbs(&rdp->cblist);
bl = max(rdp->blimit, pending >> rcu_divisor);
div = READ_ONCE(rcu_divisor);
div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
bl = max(rdp->blimit, pending >> div);
if (unlikely(bl > 100))
tlimit = local_clock() + rcu_resched_ns;
trace_rcu_batch_start(rcu_state.name,