linux-kernel - [PATCH] kernel/perf: correct return code of rb_alloc_aux() if !has

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Date:   Tue, 20 Jun 2017 12:26:39 +0200
From:   Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Pu Hou <bjhoupu@...ux.vnet.ibm.com>,
        Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>
Subject: [PATCH] kernel/perf: correct return code of rb_alloc_aux() if !has_aux(ev)

If the event for which an AUX area is about to be allocated, does
not support setting up an AUX area, rb_alloc_aux() return -ENOTSUPP.

This error condition is being returned unfiltered to the user space,
and, for example, the perf tools fails with:

  failed to mmap with 524 (INTERNAL ERROR: strerror_r(524, 0x3fff497a1c8, 512)=22)

This error can be easily seen with "perf record -m 128,256 -e cpu-clock".

The 524 error code maps to -ENOTSUPP (in rb_alloc_aux()). The -ENOTSUPP
error code shall be only used within the kernel.  So the correct error
code would then be -EOPNOTSUPP.

With this commit, the perf tool then reports:

  failed to mmap with 95 (Operation not supported)

which is more clear.

Cc: Pu Hou <bjhoupu@...ux.vnet.ibm.com>
Cc: Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>
Signed-off-by: Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
---
 kernel/events/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 2831480..ee97196 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -580,7 +580,7 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
 	int ret = -ENOMEM, max_order = 0;

 	if (!has_aux(event))
-		return -ENOTSUPP;
+		return -EOPNOTSUPP;

 	if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
 		/*
-- 
1.8.3.1