From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 9 Feb 2016 20:11:26 +0000 (+0000)
Subject: perf/core: Remove the bogus and dangerous CPU_DOWN_FAILED hotplug state
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=27ca9236c96f4a21b72a2b4f08260efeab951bd0;p=openwrt%2Fstaging%2Fblogic.git

perf/core: Remove the bogus and dangerous CPU_DOWN_FAILED hotplug state

If CPU_DOWN_PREPARE fails the perf hotplug notifier is called for
CPU_DOWN_FAILED and calls perf_event_init_cpu(), which checks whether the
swhash is referenced. If yes it allocates a new hash and stores the pointer in
the per cpu data structure.

But at this point the cpu is still online, so there must be a valid hash
already. By overwriting the pointer the existing hash is not longer
accessible.

Remove the CPU_DOWN_FAILED state, as there is nothing to (re)allocate.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20160209201007.763417379@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 474ffeafe363..4aa64a85a7b7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9282,7 +9282,6 @@ perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
 	switch (action & ~CPU_TASKS_FROZEN) {
 
 	case CPU_UP_PREPARE:
-	case CPU_DOWN_FAILED:
 		perf_event_init_cpu(cpu);
 		break;