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From: Rick Macklem <rmacklem@FreeBSD.org>
Date: Fri, 10 Sep 2010 23:49:33 +0000 (UTC)
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Subject: svn commit: r212443 - head/sys/fs/nfsserver
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Author: rmacklem
Date: Fri Sep 10 23:49:33 2010
New Revision: 212443
URL: http://svn.freebsd.org/changeset/base/212443

Log:
  This patch applies one of the two fixes suggested by
  zack.kirsch at isilon.com for a race between nfsrv_freeopen()
  and nfsrv_getlockfile() in the experimental NFS server that
  he found during testing. Although nfsrv_freeopen() holds a
  sleep lock on the lock file structure when called with
  cansleep != 0, nfsrv_getlockfile() could still search the
  list, once it acquired the NFSLOCKSTATE() mutex. I believe
  that acquiring the mutex in nfsrv_freeopen() fixes the race.
  
  MFC after:	2 weeks

Modified:
  head/sys/fs/nfsserver/nfs_nfsdstate.c

Modified: head/sys/fs/nfsserver/nfs_nfsdstate.c
==============================================================================
--- head/sys/fs/nfsserver/nfs_nfsdstate.c	Fri Sep 10 23:38:18 2010	(r212442)
+++ head/sys/fs/nfsserver/nfs_nfsdstate.c	Fri Sep 10 23:49:33 2010	(r212443)
@@ -1085,8 +1085,11 @@ nfsrv_freeopen(struct nfsstate *stp, vno
 	 * associated with the open.
 	 * If there are locks associated with the open, the
 	 * nfslockfile structure can be freed via nfsrv_freelockowner().
-	 * (That is why the call must be here instead of after the loop.)
+	 * Acquire the state mutex to avoid races with calls to
+	 * nfsrv_getlockfile().
 	 */
+	if (cansleep != 0)
+		NFSLOCKSTATE();
 	if (lfp != NULL && LIST_EMPTY(&lfp->lf_open) &&
 	    LIST_EMPTY(&lfp->lf_deleg) && LIST_EMPTY(&lfp->lf_lock) &&
 	    LIST_EMPTY(&lfp->lf_locallock) && LIST_EMPTY(&lfp->lf_rollback) &&
@@ -1096,6 +1099,8 @@ nfsrv_freeopen(struct nfsstate *stp, vno
 		ret = 1;
 	} else
 		ret = 0;
+	if (cansleep != 0)
+		NFSUNLOCKSTATE();
 	FREE((caddr_t)stp, M_NFSDSTATE);
 	newnfsstats.srvopens--;
 	nfsrv_openpluslock--;