Edit report at http://bugs.php.net/bug.php?id=31749&edit=1
ID: 31749
Comment by: michael at makeweb dot no
Reported by: phpbug2 at mailinator dot com
Summary: deadlock due to libc mutexes not released when timeout
signal is delivered
Status: No Feedback
Type: Bug
Package: Scripting Engine problem
Operating System: Linux 2.4.28, 2.4.21-SMP
PHP Version: 5CVS, 4CVS (2005-06-19)
Assigned To: dmitry
New Comment:
I have the same problem, reproduced on php 4.4.9 and 5.3.0.
Basically pseudocode to reproduce is set_time_limit(1); do { ... } until
time passed = 1 second.
This will create a race condition where sometimes a libc lock will
prevent zend_timeout to process properly.
Script to reproduce on 5.3.0: ($limit is not 1, because php seems to not
break accurately on time - this value must be adjusted so the error "PHP
Fatal error: Maximum execution time of 1 second exceeded in Unknown on
line 0" frequently appears. The script should fail within 100 runs (lock
up).
<?php
echo "Trying to break php...\n";
set_time_limit(1);
$limit = 1.235;
$start = array_sum(explode(' ',$x = microtime()));
$a = array();
for ($cnt = 0; $cnt < 10; $cnt++) {
for ($cntb = 0; $cntb < 100; $cntb++) {
for ($cntc = 0; $cntc < 100; $cntc++) {
$end = array_sum(explode(' ',$y = microtime()));
$a[$cnt][$cntb][$cntc] = md5($cnt.$cntb.$cntc);
if ($end >= $start+$limit) break;
}
if ($end >= $start+$limit) break;
}
if ($end >= $start+$limit) break;
}
echo "$x - $y (".($end-$start).")\n";
?>
run with: while [ true ]; do php break.php; done
Though this scenario is unlikely, there are other cases where it can
happen very often, however I fail to come up with a short example of it.
The reason for generating a multidimensional array is that in php4, the
hang is very likely to happen within zend_shutdown, as the resources are
freed (hangs within 1-10 cycles)
Keep in mind error logging has to be enabled (this is when there's calls
for libc "get time" which causes the locking issue within zend_timeout)
pstack for php 5.3.0:
# pstack 1565
#0 0x00319402 in __kernel_vsyscall ()
#1 0x001dede3 in __lll_lock_wait_private () from /lib/libc.so.6
#2 0x0016e6f6 in _L_lock_15330 () from /lib/libc.so.6
#3 0x0016dbb4 in free () from /lib/libc.so.6
#4 0x0012067c in setlocale () from /lib/libc.so.6
#5 0x08084586 in seek_to_tz_position ()
#6 0x08084664 in timelib_timezone_id_is_valid ()
#7 0x0806575c in guess_timezone ()
#8 0x080657a5 in get_timezone_info ()
#9 0x08067f35 in php_format_date ()
#10 0x082ab96e in php_log_err ()
#11 0x082abe17 in php_error_cb ()
#12 0x082f9fe8 in zend_error_noreturn ()
#13 0x082ec745 in zend_timeout ()
#14 <signal handler called>
#15 0x00169c49 in _int_free () from /lib/libc.so.6
#16 0x0016dbc0 in free () from /lib/libc.so.6
#17 0x082ac6df in php_conv_fp ()
#18 0x082ad409 in strx_printv ()
#19 0x082ad804 in ap_php_snprintf ()
#20 0x082565f2 in _php_gettimeofday ()
#21 0x08342509 in zend_do_fcall_common_helper_SPEC ()
#22 0x08319f3d in execute ()
#23 0x082f8e47 in zend_execute_scripts ()
#24 0x082a92be in php_execute_script ()
#25 0x08378457 in main ()
Any suggestions how to patch php4 be greatly appreciated!
Michael
Previous Comments:
------------------------------------------------------------------------
[2008-07-21 01:00:00] php-bugs at lists dot php dot net
No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".
------------------------------------------------------------------------
[2008-07-13 15:51:47] [email protected]
Please try using this CVS snapshot:
http://snaps.php.net/php5.2-latest.tar.gz
For Windows (zip):
http://snaps.php.net/win32/php5.2-win32-latest.zip
For Windows (installer):
http://snaps.php.net/win32/php5.2-win32-installer-latest.msi
------------------------------------------------------------------------
[2005-12-24 02:46:25] [email protected]
Dmitry, can you check this out please?
------------------------------------------------------------------------
[2005-02-20 15:55:55] [email protected]
Andi, please take a look. I remember some talk in the past about going
this route, but I don't recall the arguments against it.
Similarly, I'm not sure that this is really a problem for PHP to fix;
given that the time() function is officially not thread-safe, it seems
wrong for the libc to mutex internally.
------------------------------------------------------------------------
[2005-02-19 22:28:32] phpbug2 at mailinator dot com
I've created a patch against 5.0.3 to implement my "soft timeout" idea
above. It will try to soft-break execution after the timeout period
elapses and then hard-break after another timeout period.
There seem to be a lot of calls to the zend_set_timeout and
zend_unset_timeout functions that I'm not too sure are helping the
situation. Here's what happens using the CLI PHP and printing whenever
certain functions are hit:
$ sapi/cli/php /www/htdocs/time.php
zend_unset_timeout()
zend_set_timeout (0)
zend_set_timeout (0)
zend_set_timeout (0)
zend_unset_timeout()
zend_set_timeout (5)
Array 2005 2217696508 Jan-01-1998 Jan 01 1998 05:00:00
Array 2005 2217696508 Jan-01-1998 Jan 01 1998 05:00:00
Array 2005 2217696510 Jan-01-1998 Jan 01 1998 05:00:00
Array 2005 2217696512 Jan-01-1998 Jan 01 1998 05:00:00
Array 2005 2217696516 Jan-01-1998 Jan 01 1998 05:00:00
Array 2005 2217696516 Jan-01-1998 Jan 01 1998 05:00:00
zend_soft_timeout()
zend_set_timeout (5)
zend_timeout()
zend_set_timeout (5)
Fatal error: Maximum execution time of 5 seconds exceeded in
/www/htdocs/time.php on line 10
zend_unset_timeout()
zend_set_timeout (30)
zend_unset_timeout()
And the patch to 5.0.3 to implement the "zend_soft_timeout" that "works
for me" in that I'm not getting any more deadlocked Apache children:
http://www.r1hosting.net/zend_timeout.patch
------------------------------------------------------------------------
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