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From: Edward Tomasz Napierala <trasz@FreeBSD.org>
Date: Thu, 5 Feb 2009 08:46:18 +0000 (UTC)
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Subject: svn commit: r188141 - head/sys/kern
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Author: trasz
Date: Thu Feb  5 08:46:18 2009
New Revision: 188141
URL: http://svn.freebsd.org/changeset/base/188141

Log:
  In some situations, mnt_lockref could go negative due to vfs_unbusy() being
  called without calling vfs_busy() first.  This made umount(8) hang waiting
  for mnt_lockref to become zero, which would never happen.
  
  Reviewed by:	kib
  Approved by:	rwatson (mentor)
  Reported by:	pho
  Found with:	stress2
  Sponsored by:	FreeBSD Foundation

Modified:
  head/sys/kern/vfs_syscalls.c

Modified: head/sys/kern/vfs_syscalls.c
==============================================================================
--- head/sys/kern/vfs_syscalls.c	Thu Feb  5 04:02:15 2009	(r188140)
+++ head/sys/kern/vfs_syscalls.c	Thu Feb  5 08:46:18 2009	(r188141)
@@ -395,14 +395,16 @@ kern_fstatfs(struct thread *td, int fd, 
 		vfs_ref(mp);
 	VOP_UNLOCK(vp, 0);
 	fdrop(fp, td);
-	if (vp->v_iflag & VI_DOOMED) {
+	if (mp == NULL) {
 		error = EBADF;
 		goto out;
 	}
 	error = vfs_busy(mp, 0);
 	vfs_rel(mp);
-	if (error)
-		goto out;
+	if (error) {
+		VFS_UNLOCK_GIANT(vfslocked);
+		return (error);
+	}
 #ifdef MAC
 	error = mac_mount_check_stat(td->td_ucred, mp);
 	if (error)