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Re: [PATCH] tail: fix a race condition
From: |
Jim Meyering |
Subject: |
Re: [PATCH] tail: fix a race condition |
Date: |
Tue, 20 Oct 2009 15:03:54 +0200 |
Giuseppe Scrivano wrote:
> 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.
Thanks for doing that.
A couple suggestions:
>>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 += $(TESTS)
>
> TESTS = \
> misc/help-version \
> + tail-2/inotify-race \
> misc/invalid-opt \
> rm/ext3-perf \
> rm/cycle \
> diff --git a/tests/tail-2/inotify-race b/tests/tail-2/inotify-race
> new file mode 100755
> index 0000000..32ebfcb
> --- /dev/null
> +++ b/tests/tail-2/inotify-race
> @@ -0,0 +1,77 @@
> +#!/bin/sh
> +# Ensure that when open creates a destination file,
> +# that file has properly restrictive permissions.
> +# Before coreutils-6.7, there was an interval in which
> +# a just-created file would have too-generous permissions.
Those comments are for the original, deleted test.
> +# Copyright (C) 2006, 2009 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 2 of the License, or
> +# (at your option) any later version.
> +
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +# GNU General Public License for more details.
> +
> +# You should have received a copy of the GNU General Public License
> +# along with this program; if not, write to the Free Software
> +# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> +# 02110-1301, USA.
> +
> +if test "$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 &
You can simplify that and remove most of the race by removing the
xnanosleep and the preceding backgrounded sleep+echo shell.
Replace the print xnanosleep command with the gdb command,
"shell echo never-seen-with-tail-7.5 >> file" to append to the file being
tailed.
> +
> +sleep 3s
> +kill $!
> +
> +test -s gdb.out || fail=1
> +
> +Exit $fail
- [PATCH] tail: fix a race condition, Giuseppe Scrivano, 2009/10/12
- Re: [PATCH] tail: fix a race condition, Jim Meyering, 2009/10/13
- Re: [PATCH] tail: fix a race condition, Giuseppe Scrivano, 2009/10/13
- Re: [PATCH] tail: fix a race condition, Giuseppe Scrivano, 2009/10/20
- Re: [PATCH] tail: fix a race condition, Pádraig Brady, 2009/10/20
- Re: [PATCH] tail: fix a race condition,
Jim Meyering <=
- Re: [PATCH] tail: fix a race condition, Giuseppe Scrivano, 2009/10/20
- Re: [PATCH] tail: fix a race condition, Jim Meyering, 2009/10/20
- Re: [PATCH] tail: fix a race condition, Giuseppe Scrivano, 2009/10/20
- Re: [PATCH] tail: fix a race condition, Jim Meyering, 2009/10/22
- Re: [PATCH] tail: fix a race condition, Jim Meyering, 2009/10/22