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Subject[PATCH] events: Annotate parent_ctx with __rcu
Date
parent_ctx is used under RCU context in kernel/events/core.c,
tell sparse about it aswell.

Fixes the following instances of sparse error:
kernel/events/core.c:3221:18: error: incompatible types in comparison
kernel/events/core.c:3222:23: error: incompatible types in comparison

This introduces the following two sparse errors:
kernel/events/core.c:3117:18: error: incompatible types in comparison
kernel/events/core.c:3121:30: error: incompatible types in comparison

Hence, use rcu_dereference() to access parent_ctx and silence
the newly introduced errors.

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
include/linux/perf_event.h | 2 +-
kernel/events/core.c | 11 ++++++++---
2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 6d4c22aee384..e18a7bdc6f98 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -810,7 +810,7 @@ struct perf_event_context {
* These fields let us detect when two contexts have both
* been cloned (inherited) from a common ancestor.
*/
- struct perf_event_context *parent_ctx;
+ struct perf_event_context __rcu *parent_ctx;
u64 parent_gen;
u64 generation;
int pin_count;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2173c23c25b4..2a8c5670b254 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3106,26 +3106,31 @@ static void ctx_sched_out(struct perf_event_context *ctx,
static int context_equiv(struct perf_event_context *ctx1,
struct perf_event_context *ctx2)
{
+ struct perf_event_context *parent_ctx1, *parent_ctx2;
+
lockdep_assert_held(&ctx1->lock);
lockdep_assert_held(&ctx2->lock);

+ parent_ctx1 = rcu_dereference(ctx1->parent_ctx);
+ parent_ctx2 = rcu_dereference(ctx2->parent_ctx);
+
/* Pinning disables the swap optimization */
if (ctx1->pin_count || ctx2->pin_count)
return 0;

/* If ctx1 is the parent of ctx2 */
- if (ctx1 == ctx2->parent_ctx && ctx1->generation == ctx2->parent_gen)
+ if (ctx1 == parent_ctx2 && ctx1->generation == ctx2->parent_gen)
return 1;

/* If ctx2 is the parent of ctx1 */
- if (ctx1->parent_ctx == ctx2 && ctx1->parent_gen == ctx2->generation)
+ if (parent_ctx1 == ctx2 && ctx1->parent_gen == ctx2->generation)
return 1;

/*
* If ctx1 and ctx2 have the same parent; we flatten the parent
* hierarchy, see perf_event_init_context().
*/
- if (ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx &&
+ if (ctx1->parent_ctx && parent_ctx1 == parent_ctx2 &&
ctx1->parent_gen == ctx2->parent_gen)
return 1;

--
2.24.1
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