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SubjectRe: [BUG] in sched fair on v3.13-rc1+ doing hotplug
On Wed, Nov 27, 2013 at 08:13:45AM -0500, Steven Rostedt wrote:
> atomic_inc(&sd->groups->sgp->nr_busy_cpus); <<---- BUG
> unlock:
> rcu_read_unlock();
> }

tip/sched/urgent has this one:

---
commit 42eb088ed246a5a817bb45a8b32fe234cf1c0f8b
Author: Peter Zijlstra <peterz@infradead.org>
Date: Tue Nov 19 16:41:49 2013 +0100

sched: Avoid NULL dereference on sd_busy

Commit 37dc6b50cee9 ("sched: Remove unnecessary iteration over sched
domains to update nr_busy_cpus") forgot to clear 'sd_busy' under some
conditions leading to a possible NULL deref in set_cpu_sd_state_idle().

Reported-by: Anton Blanchard <anton@samba.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131118113701.GF3866@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c1808606ee5f..a1591ca7eb5a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4910,8 +4910,9 @@ static void update_top_cache_domain(int cpu)
if (sd) {
id = cpumask_first(sched_domain_span(sd));
size = cpumask_weight(sched_domain_span(sd));
- rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent);
+ sd = sd->parent; /* sd_busy */
}
+ rcu_assign_pointer(per_cpu(sd_busy, cpu), sd);

rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
per_cpu(sd_llc_size, cpu) = size;

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