Re: [PATCH] tail: fix a race condition

[Giuseppe Scrivano]

Hello,

I wrote a simple test case, taking some ideas from the old commit
11b626c20fbc65c668081996bfb9d1118f475eda.

The test has a race (it is funny, considering that it checks for a race)
and I used quite long time periods to minimize it, probably under high
loads it can cause a false positive.

Cheers,
Giuseppe


>From e86c16342e856bec744ea01b8a2f8ab1b8695d63 Mon Sep 17 00:00:00 2001
From: Giuseppe Scrivano <address@hidden>
Date: Tue, 20 Oct 2009 10:49:17 +0200
Subject: [PATCH] tests: add a new test that checks for a possible `tail' race.

If new data is available between the initial read and tail registers the inotify
watch descriptors, ensure that it is read before a new event happens on the
file.

* tests/Makefile.am (TESTS): Add tail-2/inotify-race.
* tests/tail-2/inotify-race: New file.
---
 tests/Makefile.am         |    1 +
 tests/tail-2/inotify-race |   77 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 0 deletions(-)
 create mode 100755 tests/tail-2/inotify-race

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 751db1c..bb11c23 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -74,6 +74,7 @@ EXTRA_DIST += $(TESTS)
 
 TESTS =                                                \
   misc/help-version                            \
+  tail-2/inotify-race                          \
   misc/invalid-opt                             \
   rm/ext3-perf                                 \
   rm/cycle                                     \
diff --git a/tests/tail-2/inotify-race b/tests/tail-2/inotify-race
new file mode 100755
index 0000000..32ebfcb
--- /dev/null
+++ b/tests/tail-2/inotify-race
@@ -0,0 +1,77 @@
+#!/bin/sh
+# Ensure that when open creates a destination file,
+# that file has properly restrictive permissions.
+# Before coreutils-6.7, there was an interval in which
+# a just-created file would have too-generous permissions.
+
+# Copyright (C) 2006, 2009 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  tail --version
+fi
+
+. $srcdir/test-lib.sh
+
+fail=0
+
+umask 2
+touch file || framework_failure
+
+( gdb --version ) > gdb.out 2>&1
+case `cat gdb.out` in
+  'GNU gdb'*) ;;
+  *) echo "$0: can't run gdb.  Skipping this test." 1>&2;
+     (exit 77); exit 77;;
+esac
+
+
+# Use `xnanosleep' to sleep the debugged process for a specified
+# amount of time.  `xnanosleep' is used by tail and the symbol is
+# exported, so we can use it without problems.
+
+gdb -nx --batch-silent              \
+    --eval-command='break tail_forever_inotify'    \
+    --eval-command='run -f file'    \
+    --eval-command='print xnanosleep (0.01)' \
+    --eval-command='quit'    \
+    $abs_top_builddir/src/tail < /dev/null > gdb.out 2>&1
+
+if test -s gdb.out; then
+  cat <<EOF 1>&2
+$0: can't set breakpoints or use xnanosleep in tail.  Skipping this test.
+EOF
+  (exit 77); exit 77
+fi
+
+(sleep 1s; echo "hello working tail" > file) &
+
+gdb -nx --batch-silent              \
+    --eval-command='break tail_forever_inotify'    \
+    --eval-command='run -f file'    \
+    --eval-command='print xnanosleep (2.0)' \
+    --eval-command='continue' \
+    --eval-command='quit'    \
+    $abs_top_builddir/src/tail < /dev/null > gdb.out &
+
+sleep 3s
+kill $!
+
+test -s gdb.out || fail=1
+
+Exit $fail
-- 
1.6.5