Hello internals, I'm trying to fix deadlock in an ancient php 5.2.17, php hangs on internal libc lock.
Backtrace follows #0 0x0000030b555024cb in ?? () from /lib/x86_64-linux-gnu/libc.so.6 #1 0x0000030b554986b8 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 #2 0x0000030b55496aa1 in free () from /lib/x86_64-linux-gnu/libc.so.6 #3 0x0000000000734989 in php_error_cb (type=1, error_filename=0x100013bbf18 "xxx", error_lineno=7, format=<optimized out>, args=<optimized out>) at main/main.c:837 #4 0x0000000000623e15 in soap_error_handler (error_num=1, error_filename=0x100013bbf18 "/class.cbase.php", error_lineno=7, format=0xa749c0 "Maximum execution time of %d second%s exceeded", args=0x3a2de4d3fa0) at //ext/soap/soap.c:2115 #5 0x0000000000777066 in zend_error (type=1, format=0xa749c0 "Maximum execution time of %d second%s exceeded") at /Zend/zend.c:976 #6 <signal handler called> #7 0x0000030b55493302 in ?? () from /lib/x86_64-linux-gnu/libc.so.6 #8 0x0000030b55496aac in free () from /lib/x86_64-linux-gnu/libc.so.6 #9 0x0000030b57f817c5 in free_root () from /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18 #10 0x0000030b57f65a34 in free_rows () from /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18 #11 0x0000030b57f6620d in mysql_free_result () from /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18 #12 0x000000000058cd1c in _free_mysql_result (rsrc=<optimized out>) at ext/mysql/php_mysql.c:275 #13 0x000000000078340e in list_entry_destructor (ptr=0x5074760) at Zend/zend_list.c:184 >From my understanding free is not safe to use in a signal handler, and this seems to be the issue here. http://marc.info/?l=php-internals&m=121999390109071&w=2 seems to address this issue but it's not present in 5.3 or later releases. Very similar deadlock but with time() instead of free(), https://bugs.php.net/bug.php?id=31749 Current php also uses free() in php_error_cb() and external destructors in list_entry_destructor() aren't protected by HANDLE_BLOCK_INTERRUPTIONS() (which seems to be a noop in fastcgi mode), so I suspect 5.5 may also contain this deadlock. main/main.c php_error_cb() 835 if (display) { 836 if (PG(last_error_message)) { 837 free(PG(last_error_message)); ... ^^^^^^ deadlock if previous free was interrupted by a timeout signal 845 PG(last_error_type) = type; 846 PG(last_error_message) = strdup(buffer); I'm thinking about "fixing" this by leaking memory pointed by PG(last_error_message) if php called when a timeout is pending (timeouts are usually very rare, php processes will eventually be restarted so this little memory waste won't have time to make any impact. Is this issue fixed in modern php ? If so I would be grateful for some information about the way it was done. This would save me a lot of time trying to trigger a non existing confition. I will try to reproduce this in a modern version of php. Thanks, Michal Grzedzicki -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
