Within ufs, the ffs_sync and ffs_fsync functions did not always

check for and/or report I/O errors. The result is that a VFS_SYNC
or VOP_FSYNC called with MNT_WAIT could loop infinitely on ufs in
the presence of a hard error writing a disk sector or in a filesystem
full condition. This patch ensures that I/O errors will always be
checked and returned.  This patch also ensures that every call to
VFS_SYNC or VOP_FSYNC with MNT_WAIT set checks for and takes
appropriate action when an error is returned.

Sponsored by:   DARPA & NAI Labs.

sys/fs/specfs/spec_vnops.c

@@ -421,8 +421,8 @@ spec_fsync(ap)
 	struct vnode *vp = ap->a_vp;
 	struct buf *bp;
 	struct buf *nbp;
-	int s;
-	int maxretry = 10000;	/* large, arbitrarily chosen */
+	int s, error = 0;
+	int maxretry = 100;	/* large, arbitrarily chosen */
 
 	if (!vn_isdisk(vp, NULL))
 		return (0);
@@ -435,6 +435,7 @@ spec_fsync(ap)
 	s = splbio();
         TAILQ_FOREACH(bp, &vp->v_dirtyblkhd, b_vnbufs) {
                 bp->b_flags &= ~B_SCANNED;
+		bp->b_error = 0;
 	}
 	splx(s);
 
@@ -481,16 +482,25 @@ spec_fsync(ap)
 			    PRIBIO + 1, "spfsyn", 0);
 		}
 		if (!TAILQ_EMPTY(&vp->v_dirtyblkhd)) {
-			if (--maxretry != 0) {
+			/*
+			 * If we are unable to write any of these buffers
+			 * then we fail now rather than trying endlessly
+			 * to write them out.
+			 */
+			TAILQ_FOREACH(bp, &vp->v_dirtyblkhd, b_vnbufs)
+				if ((error = bp->b_error) == 0)
+					continue;
+			if (error == 0 && --maxretry >= 0) {
 				splx(s);
 				goto loop1;
 			}
 			vprint("spec_fsync: giving up on dirty", vp);
+			error = EAGAIN;
 		}
 	}
 	VI_UNLOCK(vp);
 	splx(s);
-	return (0);
+	return (error);
 }
 
 /*

sys/kern/vfs_subr.c

@@ -3425,7 +3425,7 @@ sync_fsync(ap)
 	struct vnode *syncvp = ap->a_vp;
 	struct mount *mp = syncvp->v_mount;
 	struct thread *td = ap->a_td;
-	int asyncflag;
+	int error, asyncflag;
 
 	/*
 	 * We only need to do something if this is a lazy evaluation.
@@ -3456,12 +3456,12 @@ sync_fsync(ap)
 	asyncflag = mp->mnt_flag & MNT_ASYNC;
 	mp->mnt_flag &= ~MNT_ASYNC;
 	vfs_msync(mp, MNT_NOWAIT);
-	VFS_SYNC(mp, MNT_LAZY, ap->a_cred, td);
+	error = VFS_SYNC(mp, MNT_LAZY, ap->a_cred, td);
 	if (asyncflag)
 		mp->mnt_flag |= MNT_ASYNC;
 	vn_finished_write(mp);
 	vfs_unbusy(mp, td);
-	return (0);
+	return (error);
 }
 
 /*

sys/kern/vfs_vnops.c

@@ -1005,19 +1005,24 @@ vn_finished_write(mp)
 /*
  * Request a filesystem to suspend write operations.
  */
-void
+int
 vfs_write_suspend(mp)
 	struct mount *mp;
 {
 	struct thread *td = curthread;
+	int error;
 
 	if (mp->mnt_kern_flag & MNTK_SUSPEND)
-		return;
+		return (0);
 	mp->mnt_kern_flag |= MNTK_SUSPEND;
 	if (mp->mnt_writeopcount > 0)
 		(void) tsleep(&mp->mnt_writeopcount, PUSER - 1, "suspwt", 0);
-	VFS_SYNC(mp, MNT_WAIT, td->td_ucred, td);
+	if ((error = VFS_SYNC(mp, MNT_WAIT, td->td_ucred, td)) != 0) {
+		vfs_write_resume(mp);
+		return (error);
+	}
 	mp->mnt_kern_flag |= MNTK_SUSPENDED;
+	return (0);
 }
 
 /*

sys/sys/vnode.h

@@ -681,7 +681,7 @@ int	vfs_object_create(struct vnode *vp, struct thread *td,
 	    struct ucred *cred);
 void	vfs_timestamp(struct timespec *);
 void	vfs_write_resume(struct mount *mp);
-void	vfs_write_suspend(struct mount *mp);
+int	vfs_write_suspend(struct mount *mp);
 int	vop_stdbmap(struct vop_bmap_args *);
 int	vop_stdgetwritemount(struct vop_getwritemount_args *);
 int	vop_stdgetpages(struct vop_getpages_args *);

sys/ufs/ffs/ffs_snapshot.c

@@ -307,7 +307,10 @@ ffs_snapshot(mp, snapfile)
 	 */
 	for (;;) {
 		vn_finished_write(wrtmp);
-		vfs_write_suspend(vp->v_mount);
+		if ((error = vfs_write_suspend(vp->v_mount)) != 0) {
+			vn_start_write(NULL, &wrtmp, V_WAIT);
+			goto out;
+		}
 		if (mp->mnt_kern_flag & MNTK_SUSPENDED)
 			break;
 		vn_start_write(NULL, &wrtmp, V_WAIT);

sys/ufs/ffs/ffs_vfsops.c

@@ -184,7 +184,11 @@ ffs_mount(mp, path, data, ndp, td)
 			/*
 			 * Flush any dirty data.
 			 */
-			VFS_SYNC(mp, MNT_WAIT, td->td_proc->p_ucred, td);
+			if ((error = VFS_SYNC(mp, MNT_WAIT,
+			    td->td_proc->p_ucred, td)) != 0) {
+				vn_finished_write(mp);
+				return (error);
+			}
 			/*
 			 * Check for and optionally get rid of files open
 			 * for writing.
@@ -1156,7 +1160,7 @@ ffs_sync(mp, waitfor, cred, td)
 		if ((error = softdep_flushworklist(ump->um_mountp, &count, td)))
 			allerror = error;
 		/* Flushed work items may create new vnodes to clean */
-		if (count) {
+		if (allerror == 0 && count) {
 			mtx_lock(&mntvnode_mtx);
 			goto loop;
 		}
@@ -1172,7 +1176,7 @@ ffs_sync(mp, waitfor, cred, td)
 		if ((error = VOP_FSYNC(devvp, cred, waitfor, td)) != 0)
 			allerror = error;
 		VOP_UNLOCK(devvp, 0, td);
-		if (waitfor == MNT_WAIT) {
+		if (allerror == 0 && waitfor == MNT_WAIT) {
 			mtx_lock(&mntvnode_mtx);
 			goto loop;
 		}