Re: [PATCH] libbacktrace: fix fd leak tests on systems with extra descriptors

[Sergei Trofimovich via Gcc-patches]

On Thu, 12 Aug 2021 16:16:04 -0700
Ian Lance Taylor <i...@google.com> wrote:

> On Thu, Aug 12, 2021 at 3:34 PM Sergei Trofimovich via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > From: Sergei Trofimovich <siarh...@google.com>
> >
> > I noticed test failures when ran gcc test suite from under mc shell.
> > mc opens fd=9 and exposes it to child processes. As a result a few
> > tests failes:
> >     FAIL: b2test_buildid
> >     FAIL: btest_gnudebuglink
> >     FAIL: btest
> >     FAIL: btest_lto
> >     FAIL: btest_alloc
> >     FAIL: ctestg
> >     FAIL: ctesta
> >     FAIL: ctestg_alloc
> >     FAIL: ctesta_alloc
> >     FAIL: dwarf5
> >     FAIL: dwarf5_alloc
> >
> > Instead of trying to close file descripts in range test polls for
> > first available file descriptor by creating it via dup(1).
> >
> > libbacktrace/
> >
> >         * btest.c (check_open_files): Use last free file descriptor as a
> >         signal for flie descriptor leak.  
> 
> This isn't a useful replacement, as this will pass as long as
> libbacktrace closes the first file descriptor that it opens.  It won't
> check whether libbacktrace left any other file descriptors open.
> 
> Perhaps at program startup we could fstat descriptors up to 10 and
> record whether they are valid, and then skip those files in
> check_open_files.

Oh, great point! Completely missed it. Changed the patch to poll for present
file descriptors with fcntl(fd, F_GETFD) to compare before/after.

-- 

  Sergei

From dba67cc728d6be521f59a4c0d3abe7879de2db4c Mon Sep 17 00:00:00 2001
From: Sergei Trofimovich <siarh...@google.com>
Date: Thu, 12 Aug 2021 23:27:00 +0100
Subject: [PATCH v2] libbacktrace: fix fd leak tests on systems with extra
 descriptors

I noticed test failures when ran gcc test suite from under mc shell.
mc opens fd=9 and exposes it to child processes. As a result a few
tests failes:
    FAIL: b2test_buildid
    FAIL: btest_gnudebuglink
    FAIL: btest
    FAIL: btest_lto
    FAIL: btest_alloc
    FAIL: ctestg
    FAIL: ctesta
    FAIL: ctestg_alloc
    FAIL: ctesta_alloc
    FAIL: dwarf5
    FAIL: dwarf5_alloc

Instead of trying to close file descripts in range test polls for
their presence with with fcntl(fd, F_GETFD) before and after test.

libbacktrace/

	* btest.c (check_open_files): Use fcntl to poll for file
	descriptor presence.
---
 libbacktrace/btest.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/libbacktrace/btest.c b/libbacktrace/btest.c
index 9f9c03babf3..c08c1540fa6 100644
--- a/libbacktrace/btest.c
+++ b/libbacktrace/btest.c
@@ -34,6 +34,7 @@ POSSIBILITY OF SUCH DAMAGE.  */
    libbacktrace library.  */
 
 #include <assert.h>
+#include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -458,6 +459,18 @@ test5 (void)
   return failures;
 }
 
+#define MAX_FDS 10
+static int fd_states[MAX_FDS];
+
+static void
+store_open_files (void)
+{
+  int i;
+
+  for (i = 0; i < MAX_FDS; i++)
+    fd_states[i] = fcntl (i, F_GETFD);
+}
+
 /* Check that are no files left open.  */
 
 static void
@@ -465,9 +478,9 @@ check_open_files (void)
 {
   int i;
 
-  for (i = 3; i < 10; i++)
+  for (i = 0; i < MAX_FDS; i++)
     {
-      if (close (i) == 0)
+      if (fcntl (i, F_GETFD) != fd_states[i])
 	{
 	  fprintf (stderr,
 		   "ERROR: descriptor %d still open after tests complete\n",
@@ -484,6 +497,7 @@ main (int argc ATTRIBUTE_UNUSED, char **argv)
 {
   state = backtrace_create_state (argv[0], BACKTRACE_SUPPORTS_THREADS,
 				  error_callback_create, NULL);
+  store_open_files ();
 
 #if BACKTRACE_SUPPORTED
   test1 ();
-- 
2.32.0

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