linux-kernel - [PATCH] perf: Fix probing for PERF_FLAG_FD

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Date:	Wed, 18 Feb 2015 19:01:12 -0500
From:	David Ahern <david.ahern@...cle.com>
To:	acme@...nel.org, linux-kernel@...r.kernel.org
Cc:	David Ahern <david.ahern@...cle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: [PATCH] perf: Fix probing for PERF_FLAG_FD_CLOEXEC flag

Commit f6edb53c4993ffe92ce521fb449d1c146cea6ec2 converted the probe to
a CPU wide event first (pid == -1). For kernels that do not support
the PERF_FLAG_FD_CLOEXEC flag the probe fails with EINVAL. Since this
errno is not handled pid is not reset to 0 and the subsequent use of
pid = -1 as an argument brings in an additional failure path if
perf_event_paranoid > 0:

$ perf record -- sleep 1
perf_event_open(..., 0) failed unexpectedly with error 13 (Permission denied)
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.007 MB /tmp/perf.data (11 samples) ]

Since this function only needs to get past this check in kernel/events/core.c:

        /* for future expandability... */
        if (flags & ~PERF_FLAG_ALL)
                return -EINVAL;

pid = 0 is sufficient to confirm if the flag is supported or not.

Also, ensure the fd of the confirmation check is closed.

Needs to go to 3.18 stable tree as well.

Signed-off-by: David Ahern <david.ahern@...cle.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/perf/util/cloexec.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
index 47b78b3f0325..3cc34edf2403 100644
--- a/tools/perf/util/cloexec.c
+++ b/tools/perf/util/cloexec.c
@@ -47,16 +47,17 @@ static int perf_flag_probe(void)
 		  err, strerror_r(err, sbuf, sizeof(sbuf)));
 
 	/* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
-	fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
+	fd = sys_perf_event_open(&attr, 0, cpu, -1, 0);
 	err = errno;
 
+	if (fd >= 0)
+		close(fd);
+
 	if (WARN_ONCE(fd < 0 && err != EBUSY,
 		      "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
 		      err, strerror_r(err, sbuf, sizeof(sbuf))))
 		return -1;
 
-	close(fd);
-
 	return 0;
 }
 
-- 
1.9.3

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