linux-kernel - [tip:perf/core] perf/core: Remove the bogus and dangerous CPU_DOWN

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Message-ID: <tip-27ca9236c96f4a21b72a2b4f08260efeab951bd0@git.kernel.org>
Date:	Wed, 17 Feb 2016 04:24:31 -0800
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	jolsa@...hat.com, vincent.weaver@...ne.edu, eranian@...gle.com,
	torvalds@...ux-foundation.org, acme@...hat.com, hpa@...or.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...nel.org
Subject: [tip:perf/core] perf/core:
  Remove the bogus and dangerous CPU_DOWN_FAILED hotplug state

Commit-ID:  27ca9236c96f4a21b72a2b4f08260efeab951bd0
Gitweb:     http://git.kernel.org/tip/27ca9236c96f4a21b72a2b4f08260efeab951bd0
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Tue, 9 Feb 2016 20:11:26 +0000
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 17 Feb 2016 10:37:29 +0100

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@...utronix.de>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Link: http://lkml.kernel.org/r/20160209201007.763417379@linutronix.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/core.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 474ffea..4aa64a8 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;