I have most of the lwip stack running in a "tcpip" thread, and stack users
in various threads synchronise with it using the netconn* API. But there is
a problem with netconn_delete and netconn_recv when they delete mboxes. A
packet, or a connection to a listening socket, may arrive in the gap
between removing mbox items, and deleting the mboxes. For example:
/* Drain the recvmbox. */
if (conn->recvmbox != SYS_MBOX_NULL) {
while (sys_arch_mbox_fetch(conn->recvmbox, &mem, 1) != SYS_ARCH_TIMEOUT) {
if (conn->type == NETCONN_TCP) {
if(mem != NULL)
pbuf_free((struct pbuf *)mem);
} else {
netbuf_delete((struct netbuf *)mem);
}
}
*** PACKET CAN ARRIVE HERE ***
sys_mbox_free(conn->recvmbox);
conn->recvmbox = SYS_MBOX_NULL;
}
In that case a sys_mbox_free can be called on a non-empty mbox. This may
either leak a pbuf, or cause an assertion in the OS from the underlying
mbox implementation. I've been thinking about how to fix this. Either new
sys_arch primitives could be added. Or, better, we could try to use
SYS_LIGHTWEIGHT_PROT, but this seems a bit dubious as we need to protect
from before the sys_arch_mbox_fetch, until the conn->recvmbox = SYS_MBOX_NULL.
This may mean calling sys_arch_mbox_fetch, which has a timeout of 1, with
the protection (of whatever form) on, which is a bad idea.
It may be possible to solve this if it is ok to assign mboxes:
SYS_ARCH_PROTECT(old_level);
tmp_mbox = conn->recvmbox;
conn->recvmbox = SYS_MBOX_NULL;
SYS_ARCH_UNPROTECT(old_level);
Is assuming mboxes are assignable a valid approach? Any other thoughts? I
can't think of any other alternative than adding to the sys_arch API.
Jifl
--
eCosCentric http://www.eCosCentric.com/ The eCos and RedBoot experts
------["The best things in life aren't things."]------ Opinions==mine
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