1. 问题背景 lwip-1.4.1 版本使用 select 函数后引发崩溃。 内部报错：sock != NULL at line 1296 in src/api/sockets.c
2. 问题描述 在多线程同时使用 lwip-1.4.1 版本的 select 函数，可能产生崩溃问题。
3. 问题分析 lwip-1.4.1 中 lwip_select 函数获取 sock 结构时，未对空指针进行处理，从而引发崩溃。多线程操作同个 socket 的场景下易复现该问题。 该 bug 在 lwip 后续版本中进行了修复。
4. 解决办法
方法 (1): 使用 lwip-2.0.3 因为 lwip-2.0.3 中已修复该 bug，切换使用即可。 xradio_skylark_sdk 中切换使用 lwip-2.0.3 的方法：在本地工程的 gcc/localconfig.mk 内部导出 __CONFIG_LWIP_V1 为 n。如下所示：
代码语言：javascript复制export __CONFIG_LWIP_V1 := n方法 (2): 合入 lwip 修复成果至 lwip-1.4.1 lwip 开源代码获取方式：
代码语言：javascript复制git clone https://git.savannah.gnu.org/git/lwip.git该 bug 在提交 5ceaed291f2c1320d36f9501fadd51923fa1c556 中修复，查看修改的代码：
代码语言：javascript复制git show 5ceaed291f2c1320d36f9501fadd51923fa1c556修改内容如下所示：
代码语言：javascript复制commit 5ceaed291f2c1320d36f9501fadd51923fa1c556
Author: sg <goldsimon@gmx.de>
Date: Sat Jan 17 21:02:58 2015 0100
fixed bug #43361 select() crashes with stale FDs
diff --git a/CHANGELOG b/CHANGELOG
index 2c9aebbb..3bf40441 100644
--- a/CHANGELOG
b/CHANGELOG
@@ -152,6 152,9 @@ HISTORY
Bugfixes:
2015-01-17: Simon Goldschmidt
* sockets.c: fixed bug #43361 select() crashes with stale FDs
2015-01-17: Simon Goldschmidt
* sockets.c/.h, memp_std.h: fixed bug #40788 "lwip_setsockopt_internal() crashes"
by rewriting set/getsockopt functions to combine checks with the actual code
diff --git a/src/api/sockets.c b/src/api/sockets.c
index 3369c6d1..4109cee4 100644
--- a/src/api/sockets.c
b/src/api/sockets.c
@@ -1209,6 1209,7 @@ lwip_select(int maxfdp1, fd_set *readset, fd_set *writeset, fd_set *exceptset,
u32_t msectimeout;
struct lwip_select_cb select_cb;
int i;
int maxfdp2;
SYS_ARCH_DECL_PROTECT(lev);
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_select(%d, %p, %p, %p, tvsec=%"S32_F" tvusec=%"S32_F")n",
@@ -1266,47 1267,69 @@ lwip_select(int maxfdp1, fd_set *readset, fd_set *writeset, fd_set *exceptset,
SYS_ARCH_UNPROTECT(lev);
/* Increase select_waiting for each socket we are interested in */
- for(i = 0; i < maxfdp1; i ) {
maxfdp2 = maxfdp1;
for (i = 0; i < maxfdp1; i ) {
if ((readset && FD_ISSET(i, readset)) ||
(writeset && FD_ISSET(i, writeset)) ||
(exceptset && FD_ISSET(i, exceptset))) {
- struct lwip_sock *sock = tryget_socket(i);
- LWIP_ASSERT("sock != NULL", sock != NULL);
struct lwip_sock *sock;
SYS_ARCH_PROTECT(lev);
- sock->select_waiting ;
- LWIP_ASSERT("sock->select_waiting overflow", sock->select_waiting > 0);
sock = tryget_socket(i);
if (sock != NULL) {
sock->select_waiting ;
LWIP_ASSERT("sock->select_waiting > 0", sock->select_waiting > 0);
} else {
/* Not a valid socket */
nready = -1;
maxfdp2 = i;
SYS_ARCH_UNPROTECT(lev);
break;
}
SYS_ARCH_UNPROTECT(lev);
}
}
- /* Call lwip_selscan again: there could have been events between
- the last scan (without us on the list) and putting us on the list! */
- nready = lwip_selscan(maxfdp1, readset, writeset, exceptset, &lreadset, &lwriteset, &lexceptset);
- if (!nready) {
- /* Still none ready, just wait to be woken */
- if (timeout == 0) {
- /* Wait forever */
- msectimeout = 0;
- } else {
- msectimeout = ((timeout->tv_sec * 1000) ((timeout->tv_usec 500)/1000));
- if (msectimeout == 0) {
- /* Wait 1ms at least (0 means wait forever) */
- msectimeout = 1;
if (nready >= 0) {
/* Call lwip_selscan again: there could have been events between
the last scan (without us on the list) and putting us on the list! */
nready = lwip_selscan(maxfdp1, readset, writeset, exceptset, &lreadset, &lwriteset, &lexceptset);
if (!nready) {
/* Still none ready, just wait to be woken */
if (timeout == 0) {
/* Wait forever */
msectimeout = 0;
} else {
msectimeout = ((timeout->tv_sec * 1000) ((timeout->tv_usec 500)/1000));
if (msectimeout == 0) {
/* Wait 1ms at least (0 means wait forever) */
msectimeout = 1;
}
}
- }
- waitres = sys_arch_sem_wait(SELECT_SEM_PTR(select_cb.sem), msectimeout);
waitres = sys_arch_sem_wait(SELECT_SEM_PTR(select_cb.sem), msectimeout);
}
}
- /* Increase select_waiting for each socket we are interested in */
- for(i = 0; i < maxfdp1; i ) {
/* Decrease select_waiting for each socket we are interested in */
for (i = 0; i < maxfdp2; i ) {
if ((readset && FD_ISSET(i, readset)) ||
(writeset && FD_ISSET(i, writeset)) ||
(exceptset && FD_ISSET(i, exceptset))) {
- struct lwip_sock *sock = tryget_socket(i);
- LWIP_ASSERT("sock != NULL", sock != NULL);
struct lwip_sock *sock;
SYS_ARCH_PROTECT(lev);
- LWIP_ASSERT("sock->select_waiting > 0", sock->select_waiting > 0);
- sock->select_waiting--;
sock = tryget_socket(i);
if (sock != NULL) {
/* @todo: what if this is a new socket (reallocated?) in this case,
select_waiting-- would be wrong (a global 'sockalloc' counter,
stored per socket could help) */
LWIP_ASSERT("sock->select_waiting > 0", sock->select_waiting > 0);
if (sock->select_waiting > 0) {
sock->select_waiting--;
}
} else {
/* Not a valid socket */
nready = -1;
}
SYS_ARCH_UNPROTECT(lev);
}
}
@@ -1330,6 1353,12 @@ lwip_select(int maxfdp1, fd_set *readset, fd_set *writeset, fd_set *exceptset,
sys_sem_free(&select_cb.sem);
#endif /* LWIP_NETCONN_SEM_PER_THREAD */
if (nready < 0) {
/* This happens when a socket got closed while waiting */
set_errno(EBADF);
return -1;
}
if (waitres == SYS_ARCH_TIMEOUT) {
/* Timeout */
LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_select: timeout expiredn"));原贴链接：https://bbs.aw-ol.com/topic/727
