[PATCH 2/3] hw-breakpoints: Improve in-kernel event creation error granularity

[Frederic Weisbecker]

In fail case, perf_event_create_kernel_counter() returns NULL instead
of an error, which doesn't help us to inform the user about the origin
of the problem from the outer most callers. Often we can just return
-EINVAL, which doesn't help anyone when it's eventually about a memory
allocation failure.

Then, this patch makes perf_event_create_kernel_counter() always
returning a detailed error code.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Prasad <prasad@xxxxxxxxxxxxxxxxxx>
---
 kernel/perf_event.c |   20 +++++++++++---------
 1 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 35df94e..34a1b9d 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4780,14 +4780,17 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
 	 */
 
 	ctx = find_get_context(pid, cpu);
-	if (IS_ERR(ctx))
-		return NULL;
+	if (IS_ERR(ctx)) {
+		err = PTR_ERR(ctx);
+		goto err_exit;
+	}
 
 	event = perf_event_alloc(attr, cpu, ctx, NULL,
 				     NULL, callback, GFP_KERNEL);
-	err = PTR_ERR(event);
-	if (IS_ERR(event))
+	if (IS_ERR(event)) {
+		err = PTR_ERR(event);
 		goto err_put_context;
+	}
 
 	event->filp = NULL;
 	WARN_ON_ONCE(ctx->parent_ctx);
@@ -4804,11 +4807,10 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
 
 	return event;
 
-err_put_context:
-	if (err < 0)
-		put_ctx(ctx);
-
-	return NULL;
+ err_put_context:
+	put_ctx(ctx);
+ err_exit:
+	return ERR_PTR(err);
 }
 EXPORT_SYMBOL_GPL(perf_event_create_kernel_counter);
 
-- 
1.6.2.3

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