Diff below prevents a future lock ordering problem between NFSnode
locks (similar to Inode locks) and the NET_LOCK().
It ensures the NET_LOCK() is always locked *after* any NFSnode lock
by fixing the UVM fault case. So we have always have:
VFS -> NFS -> NFSnode lock -> socket -> NET_LOCK().
Ok?
Index: uvm/uvm_vnode.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_vnode.c,v
retrieving revision 1.99
diff -u -p -r1.99 uvm_vnode.c
--- uvm/uvm_vnode.c 8 Mar 2018 22:04:18 -0000 1.99
+++ uvm/uvm_vnode.c 20 Mar 2018 12:58:17 -0000
@@ -1105,6 +1105,7 @@ uvn_io(struct uvm_vnode *uvn, vm_page_t
off_t file_offset;
int waitf, result, mapinflags;
size_t got, wanted;
+ int netlocked = 0;
/* init values */
waitf = (flags & PGO_SYNCIO) ? M_WAITOK : M_NOWAIT;
@@ -1174,18 +1175,24 @@ uvn_io(struct uvm_vnode *uvn, vm_page_t
* Ideally, this kind of operation *should* work.
*/
result = 0;
- if ((uvn->u_flags & UVM_VNODE_VNISLOCKED) == 0)
- result = vn_lock(vn, LK_EXCLUSIVE | LK_RECURSEFAIL, curproc);
-
- if (result == 0) {
- int netlocked = (rw_status(&netlock) == RW_WRITE);
-
+ if ((uvn->u_flags & UVM_VNODE_VNISLOCKED) == 0) {
/*
* This process may already have the NET_LOCK(), if we
* faulted in copyin() or copyout() in the network stack.
*/
- if (netlocked)
+ if (rw_status(&netlock) == RW_WRITE) {
+ netlocked = 1;
+ NET_UNLOCK();
+ }
+
+ result = vn_lock(vn, LK_EXCLUSIVE | LK_RECURSEFAIL, curproc);
+ }
+
+ if (result == 0) {
+ if (!netlocked && (rw_status(&netlock) == RW_WRITE)) {
+ netlocked = 1;
NET_UNLOCK();
+ }
/* NOTE: vnode now locked! */
if (rw == UIO_READ)
@@ -1195,11 +1202,12 @@ uvn_io(struct uvm_vnode *uvn, vm_page_t
(flags & PGO_PDFREECLUST) ? IO_NOCACHE : 0,
curproc->p_ucred);
+ if ((uvn->u_flags & UVM_VNODE_VNISLOCKED) == 0)
+ VOP_UNLOCK(vn, curproc);
+
if (netlocked)
NET_LOCK();
- if ((uvn->u_flags & UVM_VNODE_VNISLOCKED) == 0)
- VOP_UNLOCK(vn, curproc);
}
/* NOTE: vnode now unlocked (unless vnislocked) */
