Turns out that the NET_LOCK() related hang reported by many is a
deadlock. One way to prevent it is to ensure that fdplock() is
always taken before the NET_LOCK() when both have to been hold.
This generates the diff below.
Comments, ok?
Index: kern/uipc_socket.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket.c,v
retrieving revision 1.171
diff -u -p -r1.171 uipc_socket.c
--- kern/uipc_socket.c 29 Dec 2016 12:12:43 -0000 1.171
+++ kern/uipc_socket.c 19 Jan 2017 09:14:22 -0000
@@ -800,9 +800,12 @@ dontblock:
if (controlp) {
if (pr->pr_domain->dom_externalize &&
mtod(cm, struct cmsghdr *)->cmsg_type ==
- SCM_RIGHTS)
- error = (*pr->pr_domain->dom_externalize)(cm,
- controllen, flags);
+ SCM_RIGHTS) {
+ NET_UNLOCK(s);
+ error = (*pr->pr_domain->dom_externalize)(
+ cm, controllen, flags);
+ NET_LOCK(s);
+ }
*controlp = cm;
} else {
/*
Index: kern/uipc_syscalls.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_syscalls.c,v
retrieving revision 1.144
diff -u -p -r1.144 uipc_syscalls.c
--- kern/uipc_syscalls.c 29 Dec 2016 12:12:43 -0000 1.144
+++ kern/uipc_syscalls.c 19 Jan 2017 09:03:56 -0000
@@ -278,6 +278,7 @@ doaccept(struct proc *p, int sock, struc
headfp = fp;
redo:
+ fdplock(fdp);
NET_LOCK(s);
head = headfp->f_data;
if (isdnssocket(head) || (head->so_options & SO_ACCEPTCONN) == 0) {
@@ -312,11 +313,9 @@ redo:
nflag = flags & SOCK_NONBLOCK_INHERIT ? (headfp->f_flag & FNONBLOCK)
: (flags & SOCK_NONBLOCK ? FNONBLOCK : 0);
- fdplock(fdp);
error = falloc(p, &fp, &tmpfd);
if (error == 0 && (flags & SOCK_CLOEXEC))
fdp->fd_ofileflags[tmpfd] |= UF_EXCLOSE;
- fdpunlock(fdp);
if (error != 0) {
/*
* Probably ran out of file descriptors. Wakeup
@@ -336,7 +335,6 @@ redo:
if (head->so_qlen == 0) {
NET_UNLOCK(s);
m_freem(nam);
- fdplock(fdp);
fdremove(fdp, tmpfd);
closef(fp, p);
fdpunlock(fdp);
@@ -365,7 +363,6 @@ redo:
/* if an error occurred, free the file descriptor */
NET_UNLOCK(s);
m_freem(nam);
- fdplock(fdp);
fdremove(fdp, tmpfd);
closef(fp, p);
fdpunlock(fdp);
@@ -377,6 +374,7 @@ redo:
m_freem(nam);
bad:
NET_UNLOCK(s);
+ fdpunlock(fdp);
out:
FRELE(headfp, p);
return (error);
