perf_events: Fix stale ->cgrp pointer in update_cgrp_time_from_cpuctx()
This patch solves a stale pointer problem in update_cgrp_time_from_cpuctx(). The cpuctx->cgrp was not cleared on all possible event exit paths, including: close() perf_release() perf_release_kernel() list_del_event() This patch fixes list_del_event() to clear cpuctx->cgrp when there are no cgroup events left in the context. [ This second version makes the code compile when CONFIG_CGROUP_PERF is not enabled. We unconditionally define perf_cpu_context->cgrp. ] Signed-off-by: Stephane Eranian <eranian@google.com> Cc: peterz@infradead.org Cc: perfmon2-devel@lists.sf.net Cc: paulus@samba.org Cc: davem@davemloft.net LKML-Reference: <20110323150306.GA1580@quad> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -938,9 +938,7 @@ struct perf_cpu_context {
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struct list_head rotation_list;
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int jiffies_interval;
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struct pmu *active_pmu;
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#ifdef CONFIG_CGROUP_PERF
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struct perf_cgroup *cgrp;
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#endif
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};
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struct perf_output_handle {
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@ -941,6 +941,7 @@ static void perf_group_attach(struct perf_event *event)
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static void
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list_del_event(struct perf_event *event, struct perf_event_context *ctx)
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{
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struct perf_cpu_context *cpuctx;
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/*
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* We can have double detach due to exit/hot-unplug + close.
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*/
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@ -949,8 +950,17 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
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event->attach_state &= ~PERF_ATTACH_CONTEXT;
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if (is_cgroup_event(event))
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if (is_cgroup_event(event)) {
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ctx->nr_cgroups--;
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cpuctx = __get_cpu_context(ctx);
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/*
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* if there are no more cgroup events
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* then cler cgrp to avoid stale pointer
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* in update_cgrp_time_from_cpuctx()
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*/
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if (!ctx->nr_cgroups)
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cpuctx->cgrp = NULL;
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}
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ctx->nr_events--;
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if (event->attr.inherit_stat)
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