perf: Avoid RCU vs preemption assumptions
The per-pmu per-cpu context patch converted things from
get_cpu_var() to this_cpu_ptr(), but that only works if
rcu_read_lock() actually disables preemption, and since
there is no such guarantee, we need to fix that.
Use the newly introduced {get,put}_cpu_ptr().
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tejun Heo <tj@kernel.org>
LKML-Reference: <20100917093009.308453028@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index baae136..c16158c 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3836,18 +3836,20 @@
rcu_read_lock();
list_for_each_entry_rcu(pmu, &pmus, entry) {
- cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+ cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);
perf_event_task_ctx(&cpuctx->ctx, task_event);
ctx = task_event->task_ctx;
if (!ctx) {
ctxn = pmu->task_ctx_nr;
if (ctxn < 0)
- continue;
+ goto next;
ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
}
if (ctx)
perf_event_task_ctx(ctx, task_event);
+next:
+ put_cpu_ptr(pmu->pmu_cpu_context);
}
rcu_read_unlock();
}
@@ -3969,16 +3971,18 @@
rcu_read_lock();
list_for_each_entry_rcu(pmu, &pmus, entry) {
- cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+ cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);
perf_event_comm_ctx(&cpuctx->ctx, comm_event);
ctxn = pmu->task_ctx_nr;
if (ctxn < 0)
- continue;
+ goto next;
ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
if (ctx)
perf_event_comm_ctx(ctx, comm_event);
+next:
+ put_cpu_ptr(pmu->pmu_cpu_context);
}
rcu_read_unlock();
}
@@ -4152,19 +4156,21 @@
rcu_read_lock();
list_for_each_entry_rcu(pmu, &pmus, entry) {
- cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+ cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);
perf_event_mmap_ctx(&cpuctx->ctx, mmap_event,
vma->vm_flags & VM_EXEC);
ctxn = pmu->task_ctx_nr;
if (ctxn < 0)
- continue;
+ goto next;
ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
if (ctx) {
perf_event_mmap_ctx(ctx, mmap_event,
vma->vm_flags & VM_EXEC);
}
+next:
+ put_cpu_ptr(pmu->pmu_cpu_context);
}
rcu_read_unlock();
