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Groups > linux.kernel > #1330631

[patch 2/4] perf: Remove the bogus and dangerous CPU_DOWN_FAILED hotplug state

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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>
---
 kernel/events/core.c |    1 -
 1 file changed, 1 deletion(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9282,7 +9282,6 @@ perf_cpu_notify(struct notifier_block *s
 	switch (action & ~CPU_TASKS_FROZEN) {
 
 	case CPU_UP_PREPARE:
-	case CPU_DOWN_FAILED:
 		perf_event_init_cpu(cpu);
 		break;
 

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Thread

[patch 0/4] perf: Fix various cpu hotplug oddities Thomas Gleixner <tglx@linutronix.de> - 2016-02-09 21:20 +0100
  [patch 2/4] perf: Remove the bogus and dangerous CPU_DOWN_FAILED  hotplug state Thomas Gleixner <tglx@linutronix.de> - 2016-02-09 21:20 +0100
    [tip:perf/core] perf/core:   Remove the bogus and dangerous CPU_DOWN_FAILED hotplug state tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-02-17 13:30 +0100
  [patch 1/4] perf: Remove bogus UP_CANCELED hotplug state Thomas Gleixner <tglx@linutronix.de> - 2016-02-09 21:20 +0100
    [tip:perf/core] perf/core: Remove bogus UP_CANCELED hotplug state tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-02-17 13:30 +0100

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