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Subject[PATCH] perf_event: Annotate rb pointer with __rcu
Date
perf_event::rb is used in RCU context, tell sparse
about it aswell to eliminate false-positives.

Fixes the following instances of sparse error:
incompatible types in comparison expression (different address spaces)
kernel/events/core.c:5596:9
kernel/events/core.c:5302:22
kernel/events/core.c:5438:14
kernel/events/core.c:5471:14
kernel/events/core.c:5528:14
kernel/events/core.c:5614:14
kernel/events/core.c:5627:14
kernel/events/core.c:7182:13
kernel/events/ring_buffer.c:169:14
kernel/events/ring_buffer.c:169:14
kernel/events/ring_buffer.c:169:14

This introduces the following 2 new sparse errors:
kernel/events/core.c:7212:9
kernel/events/core.c:5749:31

which are fixed by using RCU primitives, rcu_dereference()
and rcu_access_pointer() on perf_event::rb.

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
include/linux/perf_event.h | 2 +-
kernel/events/core.c | 5 +++--
2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 6d4c22aee384..1691107d2800 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -694,7 +694,7 @@ struct perf_event {
struct mutex mmap_mutex;
atomic_t mmap_count;

- struct ring_buffer *rb;
+ struct ring_buffer __rcu *rb;
struct list_head rb_entry;
unsigned long rcu_batches;
int rcu_pending;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2173c23c25b4..7b9411d21165 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5746,7 +5746,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
* still restart the iteration to make sure we're not now
* iterating the wrong list.
*/
- if (event->rb == rb)
+ if (rcu_access_pointer(event->rb) == rb)
ring_buffer_attach(event, NULL);

mutex_unlock(&event->mmap_mutex);
@@ -7209,7 +7209,8 @@ static void perf_pmu_output_stop(struct perf_event *event)

restart:
rcu_read_lock();
- list_for_each_entry_rcu(iter, &event->rb->event_list, rb_entry) {
+ list_for_each_entry_rcu(iter, &rcu_dereference(event->rb)->event_list,
+ rb_entry) {
/*
* For per-CPU events, we need to make sure that neither they
* nor their children are running; for cpu==-1 events it's
--
2.24.1
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