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authorPaul Mackerras <paulus@samba.org>2010-03-10 04:45:52 -0500
committerIngo Molnar <mingo@elte.hu>2010-03-11 06:43:51 -0500
commit220b140b52ab6cc133f674a7ffec8fa792054f25 (patch)
treedf8d370f604f84145b1ba5d056d4622b6c85b488 /kernel
parent97d5a22005f38057b4bc0d95f81cd26510268794 (diff)
perf_event: Fix oops triggered by cpu offline/online
Anton Blanchard found that he could reliably make the kernel hit a BUG_ON in the slab allocator by taking a cpu offline and then online while a system-wide perf record session was running. The reason is that when the cpu comes up, we completely reinitialize the ctx field of the struct perf_cpu_context for the cpu. If there is a system-wide perf record session running, then there will be a struct perf_event that has a reference to the context, so its refcount will be 2. (The perf_event has been removed from the context's group_entry and event_entry lists by perf_event_exit_cpu(), but that doesn't remove the perf_event's reference to the context and doesn't decrement the context's refcount.) When the cpu comes up, perf_event_init_cpu() gets called, and it calls __perf_event_init_context() on the cpu's context. That resets the refcount to 1. Then when the perf record session finishes and the perf_event is closed, the refcount gets decremented to 0 and the context gets kfreed after an RCU grace period. Since the context wasn't kmalloced -- it's part of a per-cpu variable -- bad things happen. In fact we don't need to completely reinitialize the context when the cpu comes up. It's sufficient to initialize the context once at boot, but we need to do it for all possible cpus. This moves the context initialization to happen at boot time. With this, we don't trash the refcount and the context never gets kfreed, and we don't hit the BUG_ON. Reported-by: Anton Blanchard <anton@samba.org> Signed-off-by: Paul Mackerras <paulus@samba.org> Tested-by: Anton Blanchard <anton@samba.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <stable@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/perf_event.c13
1 files changed, 12 insertions, 1 deletions
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index c502b18594cc..fb3031cf9f17 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5368,12 +5368,22 @@ int perf_event_init_task(struct task_struct *child)
5368 return ret; 5368 return ret;
5369} 5369}
5370 5370
5371static void __init perf_event_init_all_cpus(void)
5372{
5373 int cpu;
5374 struct perf_cpu_context *cpuctx;
5375
5376 for_each_possible_cpu(cpu) {
5377 cpuctx = &per_cpu(perf_cpu_context, cpu);
5378 __perf_event_init_context(&cpuctx->ctx, NULL);
5379 }
5380}
5381
5371static void __cpuinit perf_event_init_cpu(int cpu) 5382static void __cpuinit perf_event_init_cpu(int cpu)
5372{ 5383{
5373 struct perf_cpu_context *cpuctx; 5384 struct perf_cpu_context *cpuctx;
5374 5385
5375 cpuctx = &per_cpu(perf_cpu_context, cpu); 5386 cpuctx = &per_cpu(perf_cpu_context, cpu);
5376 __perf_event_init_context(&cpuctx->ctx, NULL);
5377 5387
5378 spin_lock(&perf_resource_lock); 5388 spin_lock(&perf_resource_lock);
5379 cpuctx->max_pertask = perf_max_events - perf_reserved_percpu; 5389 cpuctx->max_pertask = perf_max_events - perf_reserved_percpu;
@@ -5439,6 +5449,7 @@ static struct notifier_block __cpuinitdata perf_cpu_nb = {
5439 5449
5440void __init perf_event_init(void) 5450void __init perf_event_init(void)
5441{ 5451{
5452 perf_event_init_all_cpus();
5442 perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_UP_PREPARE, 5453 perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_UP_PREPARE,
5443 (void *)(long)smp_processor_id()); 5454 (void *)(long)smp_processor_id());
5444 perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_ONLINE, 5455 perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_ONLINE,