Commit-ID: 9886167d20c0720dcfb01e62cdff4d906b226f43
Gitweb: http://git.kernel.org/tip/9886167d20c0720dcfb01e62cdff4d906b226f43
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 3 Oct 2013 16:02:23 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 4 Oct 2013 09:58:53 +0200
perf: Fix perf_pmu_migrate_context
While auditing the list_entry usage due to a trinity bug I found that
perf_pmu_migrate_context violates the rules for
perf_event::event_entry.
The problem is that perf_event::event_entry is a RCU list element, and
hence we must wait for a full RCU grace period before re-using the
element after deletion.
Therefore the usage in perf_pmu_migrate_context() which re-uses the
entry immediately is broken. For now introduce another list_head into
perf_event for this specific usage.
This doesn't actually fix the trinity report because that never goes
through this code.
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-mkj72lxagw1z8fvjm648iznw@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/perf_event.h | 24 +++++++++++++++++++++++-
kernel/events/core.c | 6 +++---
2 files changed, 26 insertions(+), 4 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 866e85c..c8ba627 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -294,9 +294,31 @@ struct ring_buffer;
*/
struct perf_event {
#ifdef CONFIG_PERF_EVENTS
- struct list_head group_entry;
+ /*
+ * entry onto perf_event_context::event_list;
+ * modifications require ctx->lock
+ * RCU safe iterations.
+ */
struct list_head event_entry;
+
+ /*
+ * XXX: group_entry and sibling_list should be mutually exclusive;
+ * either you're a sibling on a group, or you're the group leader.
+ * Rework the code to always use the same list element.
+ *
+ * Locked for modification by both ctx->mutex and ctx->lock; holding
+ * either sufficies for read.
+ */
+ struct list_head group_entry;
struct list_head sibling_list;
+
+ /*
+ * We need storage to track the entries in perf_pmu_migrate_context; we
+ * cannot use the event_entry because of RCU and we want to keep the
+ * group in tact which avoids us using the other two entries.
+ */
+ struct list_head migrate_entry;
+
struct hlist_node hlist_entry;
int nr_siblings;
int group_flags;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index cb4238e..d49a9d2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7234,15 +7234,15 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu)
perf_remove_from_context(event);
unaccount_event_cpu(event, src_cpu);
put_ctx(src_ctx);
- list_add(&event->event_entry, &events);
+ list_add(&event->migrate_entry, &events);
}
mutex_unlock(&src_ctx->mutex);
synchronize_rcu();
mutex_lock(&dst_ctx->mutex);
- list_for_each_entry_safe(event, tmp, &events, event_entry) {
- list_del(&event->event_entry);
+ list_for_each_entry_safe(event, tmp, &events, migrate_entry) {
+ list_del(&event->migrate_entry);
if (event->state >= PERF_EVENT_STATE_OFF)
event->state = PERF_EVENT_STATE_INACTIVE;
account_event_cpu(event, dst_cpu);
--
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