hw-breakpoints: Improve in-kernel event creation error granularity

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
return a detailed error code.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
LKML-Reference: <1259210142-5714-2-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 35df94e344f2b8acc4fc927e1aaf7426f9cd534d..34a1b9d7633e83aee544335f09185c3658db1564 100644 (file)
--- 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);