Fix a race that can occur when nfs nfsiod threads are being created.

Without this patch it was possible for a different thread that calls
nfs_asyncio() to snitch a newly created nfsiod thread that was
intended for another caller of nfs_asyncio(), because the nfs_iod_mtx
mutex was unlocked while the new nfsiod thread was created. This patch
labels the newly created nfsiod, so that it is not taken by another
caller of nfs_asyncio(). This is believed to fix the problem reported
on the freebsd-stable email list under the subject:
FreeBSD NFS client/Linux NFS server issue.

Tested by:	to DOT my DOT trociny AT gmail DOT com
Reviewed by:	jhb
MFC after:	2 weeks

1 files changed, 3 insertions, 3 deletions

diff --git a/sys/nfsclient/nfs_bio.c b/sys/nfsclient/nfs_bio.c
index 945bc51..cec0220 100644
--- a/sys/nfsclient/nfs_bio.c
+++ b/sys/nfsclient/nfs_bio.c
@@ -1377,7 +1377,7 @@ again:
 	 * Find a free iod to process this request.
 	 */
 	for (iod = 0; iod < nfs_numasync; iod++)
-		if (nfs_iodwant[iod]) {
+		if (nfs_iodwant[iod] == NFSIOD_AVAILABLE) {
 			gotiod = TRUE;
 			break;
 		}
@@ -1386,7 +1386,7 @@ again:
 	 * Try to create one if none are free.
 	 */
 	if (!gotiod) {
-		iod = nfs_nfsiodnew();
+		iod = nfs_nfsiodnew(1);
 		if (iod != -1)
 			gotiod = TRUE;
 	}
@@ -1398,7 +1398,7 @@ again:
 		 */
 		NFS_DPF(ASYNCIO, ("nfs_asyncio: waking iod %d for mount %p\n",
 		    iod, nmp));
-		nfs_iodwant[iod] = NULL;
+		nfs_iodwant[iod] = NFSIOD_NOT_AVAILABLE;
 		nfs_iodmount[iod] = nmp;
 		nmp->nm_bufqiods++;
 		wakeup(&nfs_iodwant[iod]);