Bug #31749 [NoF->ReO]: deadlock due to libc mutexes not released when timeout signal is delivered

Edit report at http://bugs.php.net/bug.php?id=31749&edit=1 ID: 31749 Updated by: mkoppanen@php.net Reported by: phpbug2 at mailinator dot com Summary: deadlock due to libc mutexes not released when timeout signal is delivered -Status: No Feedback +Status: Re-Opened 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 Previous Comments: ------------------------------------------------------------------------ [2010-06-08 13:27:41] michael at makeweb dot no 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 ------------------------------------------------------------------------ [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] jani@php.net 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] sniper@php.net Dmitry, can you check this out please? ------------------------------------------------------------------------ [2005-02-20 15:55:55] wez@php.net 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. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/bug.php?id=31749 -- Edit this bug report at http://bugs.php.net/bug.php?id=31749&edit=1