[src/trunk]: src/sys/nfs Commit fix for NFS write deadlock, on filesystems mo...

[jonathan <jonathan%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c907ade54605
branches:  trunk
changeset: 555419:c907ade54605
user:      jonathan <jonathan%NetBSD.org@localhost>
date:      Mon Nov 17 00:28:32 2003 +0000

description:
Commit fix for NFS write deadlock, on filesystems mounted via
local-loopback (lo0). As posted for review on tech-kern 2003-18-09,
with a long  comment explaining (one of) the deadlock scenarios.

I've used this since shortly after 2002-09-12-, without noticing
performance degradataion or instability for non-loopback mounts.

diffstat:

 sys/nfs/nfs_bio.c |  16 +++++++++++-----
 1 files changed, 11 insertions(+), 5 deletions(-)

diffs (38 lines):

diff -r 042f03d30d4e -r c907ade54605 sys/nfs/nfs_bio.c
--- a/sys/nfs/nfs_bio.c Mon Nov 17 00:02:33 2003 +0000
+++ b/sys/nfs/nfs_bio.c Mon Nov 17 00:28:32 2003 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: nfs_bio.c,v 1.110 2003/09/26 11:51:53 yamt Exp $       */
+/*     $NetBSD: nfs_bio.c,v 1.111 2003/11/17 00:28:32 jonathan Exp $   */
 
 /*
  * Copyright (c) 1989, 1993
@@ -35,7 +35,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: nfs_bio.c,v 1.110 2003/09/26 11:51:53 yamt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: nfs_bio.c,v 1.111 2003/11/17 00:28:32 jonathan Exp $");
 
 #include "opt_nfs.h"
 #include "opt_ddb.h"
@@ -836,10 +836,16 @@
 
        /*
         * If we have an iod which can process the request, then queue
-        * the buffer.
+        * the buffer.  However, even if we have an iod, do not initiate 
+        * queue cleaning if curproc is the pageout daemon. if the NFS mount
+        * is via local loopback, we may put curproc (pagedaemon) to sleep
+        * waiting for the writes to complete. But the server (ourself)
+        * may block the write, waiting for its (ie., our) pagedaemon
+        * to produce clean pages to handle the write: deadlock.
+        * XXX: start non-loopback mounts straight away?  If "lots free",
+        * let pagedaemon start loopback writes anyway?
         */
-
-       if (gotiod) {
+       if (gotiod && (curproc != uvm.pagedaemon_proc)) {
 
                /*
                 * Ensure that the queue never grows too large.