前几天东政同学反馈说Linode服务器快卡死了，今天有时间排查了一下具体原因，最终原因稍微有点悲壮：file_get_contents没有设置超时时间，加上我用的php5.2关于curl的代码有个bug，于是导致PHP进程进入死循环。
今天下午又发现系统负载很高，于是上去看了一下，发现一大坨PHP进程没有退出，占用了很多CPU，如图：
问题进程：
后面运行的脚本是我的RSS定时更新任务，看来PHP代码什么地方有问题，于是strace -p 14043看了一下：
select(5, [4], [4], [], {15, 0}) = 1 (out [4], left {14, 999996}) poll([{fd=4, events=POLLIN|POLLPRI}], 1, 0) = 0 (Timeout) clock_gettime(CLOCK_MONOTONIC, {4582888, 760370017}) = 0 clock_gettime(CLOCK_MONOTONIC, {4582888, 760468615}) = 0 clock_gettime(CLOCK_MONOTONIC, {4582888, 760565053}) = 0 select(5, [4], [4], [], {15, 0}) = 1 (out [4], left {14, 999997})
在４号fd上面死循环了，于是看看FD是什么：ll /proc/14043/fd
lrwx—— 1 wuhaiwen wuhaiwen 64 7月 21 11:00 4 -> socket:[53176380]
再看了一下原来是在请求CSDN的一个网页的时候死循环了，但不知道什么地方请求的，想到GDB一下php进程看看，bt显示：
(gdb) bt
#0 0x00007f6721f8f013 in __select_nocancel () at ../sysdeps/unix/syscall-template.S:82
#1 0×0000000000481952 in php_curl_stream_read (stream=0×2280650,
buf=0x22ea5d0 “2F%2Ftag%2F%25e6%25ad%25a3%25e5%2588%2599%27+class%3D%27tag-link-191%27+title%3D%273+topics%27+style%3D%27font-size%3A+9.0243902439pt%3B%27%3E%E6%AD%A3%E5%88%99%3C%2Fa%3E%3C%2Ftags%3E\”"…, count=8192) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/ext/curl/streams.c:169
#2 0x00000000006738f9 in php_stream_fill_read_buffer (stream=0×2280650, size=4283) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/main/streams/streams.c:554
#3 0x0000000000673c39 in _php_stream_read (stream=0×2280650,
buf=0x2301fd5 “f='http://www.laruence.com/tag/json'3 topics'>json</a>\n<a href='https://www.laruence.com/tag/module'2 topics' “…, size=4283) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/main/streams/streams.c:600
#4 0x0000000000674c51 in _php_stream_copy_to_mem (src=0×2280650, buf=0x7fff376ed898, maxlen=<optimized out>, persistent=0)
at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/main/streams/streams.c:1267
#5 0x00000000005fdb85 in zif_file_get_contents (ht=<optimized out>, return_value=0x2223da0, return_value_ptr=<optimized out>, this_ptr=<optimized out>, return_value_used=<optimized out>)
at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/ext/standard/file.c:565
#6 0x00000000006c2a59 in zend_do_fcall_common_helper_SPEC (execute_data=0x7fff376edc60) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/Zend/zend_vm_execute.h:200
#7 0x00000000006c239f in execute (op_array=0x1f26730) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/Zend/zend_vm_execute.h:92
·············
#16 0x0000000000730d8e in main (argc=4, argv=0x7fff376f2468) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/sapi/cli/php_cli.c:1133
看一下当前PHP执行的脚步是什么：
(gdb) p *op_array $4 = {type = 2 '\002', function_name = 0x1e54278 "getContent", scope = 0x1f8e850, fn_flags = 257, prototype = 0x0, num_args = 2, required_num_args = 1, arg_info = 0x1fd5e20, pass_rest_by_reference = 0 '\000', return_reference = 0 '\000', refcount = 0x1fd3ab8, opcodes = 0x1fddcc8, last = 28, size = 28, vars = 0x1fd3cc0, last_var = 6, size_var = 16, T = 15, brk_cont_array = 0x0, last_brk_cont = 0, current_brk_cont = 4294967295, try_catch_array = 0x0, last_try_catch = 0, static_variables = 0x0, start_op = 0x0, backpatch_count = 0, done_pass_two = 1 '\001', uses_this = 0 '\000', filename = 0x1fd3b58 "/home/wuhaiwen/webroot/kulvrss/libs/Myrss/Model/UrlContenter.php", line_start = 9, line_end = 30, doc_comment = 0x0, doc_comment_len = 0, reserved = {0x0, 0x0, 0x0, 0x0}}
找到了问题代码位置，原来是一个file_get_contents($url)调用，没有设置超时时间，于是PHP卡死在网络请求了。于是用stream_context_create 设置超时时间搞定。
到这里 似乎问题解决了，但是，为什么没有设置超时时间就导致php进程占用CPU，系统负载那么高？按理说应该等待I/O才是呀？看上面CPU情况，完全是进入了死循环的节奏。
根据上面的bt堆栈，首先看倒数第二个函数的调用：
#1 0×0000000000481952 in php_curl_stream_read (stream=0×2280650,
buf=0x22ea5d0 “2F%2Ftag%2F%25e6%25ad%25a3%25e5%2588%2599%27+class%3D%27tag-link-191%27+title%3D%273+topics%27+style%3D%27font-size%3A+9.0243902439pt%3B%27%3E%E6%AD%A3%E5%88%99%3C%2Fa%3E%3C%2Ftags%3E\”"…, count=8192) at /home/wuhaiwen/install/php-env/src/php/php-5.2.8/ext/curl/streams.c:169
看一下代码，我用的事5.2.8版本的PHP，比较老。代码如下：