- Add locking to all filesystem operations in fdescfs and flag it as MPSAFE.

- Use proper synhronization primitives to protect the internal fdesc node cache
  used in fdescfs.
- Properly initialize and uninitalize hash.
- Remove unused functions.

Since fdescfs might recurse on itself, adding proper locking to it needed some
tricky workarounds in some parts to make it work. For instance, a descriptor in
fdescfs could refer to an open descriptor to itself, thus forcing the thread to
recurse on vnode locks. Because of this, other race conditions also had to be
fixed.

Tested by:	pho
Reviewed by:	kib (mentor)
Approved by:	kib (mentor)

1 files changed, 158 insertions, 72 deletions

diff --git a/sys/fs/fdescfs/fdesc_vnops.c b/sys/fs/fdescfs/fdesc_vnops.c
index 06b1718..1fbd41e 100644
--- a/sys/fs/fdescfs/fdesc_vnops.c
+++ b/sys/fs/fdescfs/fdesc_vnops.c
@@ -56,18 +56,15 @@
 
 #include <fs/fdescfs/fdesc.h>
 
-#define FDL_WANT	0x01
-#define FDL_LOCKED	0x02
-static int fdcache_lock;
-
 #define	NFDCACHE 4
 #define FD_NHASH(ix) \
 	(&fdhashtbl[(ix) & fdhash])
 static LIST_HEAD(fdhashhead, fdescnode) *fdhashtbl;
 static u_long fdhash;
 
+struct mtx fdesc_hashmtx;
+
 static vop_getattr_t	fdesc_getattr;
-static vop_inactive_t	fdesc_inactive;
 static vop_lookup_t	fdesc_lookup;
 static vop_open_t	fdesc_open;
 static vop_readdir_t	fdesc_readdir;
@@ -79,7 +76,6 @@ static struct vop_vector fdesc_vnodeops = {
 
 	.vop_access =		VOP_NULL,
 	.vop_getattr =		fdesc_getattr,
-	.vop_inactive =		fdesc_inactive,
 	.vop_lookup =		fdesc_lookup,
 	.vop_open =		fdesc_open,
 	.vop_pathconf =		vop_stdpathconf,
@@ -88,6 +84,9 @@ static struct vop_vector fdesc_vnodeops = {
 	.vop_setattr =		fdesc_setattr,
 };
 
+static void fdesc_insmntque_dtr(struct vnode *, void *);
+static void fdesc_remove_entry(struct fdescnode *);
+
 /*
  * Initialise cache headers
  */
@@ -96,81 +95,154 @@ fdesc_init(vfsp)
 	struct vfsconf *vfsp;
 {
 
+	mtx_init(&fdesc_hashmtx, "fdescfs_hash", NULL, MTX_DEF);
 	fdhashtbl = hashinit(NFDCACHE, M_CACHE, &fdhash);
 	return (0);
 }
 
+/*
+ * Uninit ready for unload.
+ */
+int
+fdesc_uninit(vfsp)
+	struct vfsconf *vfsp;
+{
+
+	hashdestroy(fdhashtbl, M_CACHE, fdhash);
+	mtx_destroy(&fdesc_hashmtx);
+	return (0);
+}
+
+/*
+ * If allocating vnode fails, call this.
+ */
+static void
+fdesc_insmntque_dtr(struct vnode *vp, void *arg)
+{
+
+	vgone(vp);
+	vput(vp);
+}
+
+/*
+ * Remove an entry from the hash if it exists.
+ */
+static void
+fdesc_remove_entry(struct fdescnode *fd)
+{
+	struct fdhashhead *fc;
+	struct fdescnode *fd2;
+
+	fc = FD_NHASH(fd->fd_ix);
+	mtx_lock(&fdesc_hashmtx);
+	LIST_FOREACH(fd2, fc, fd_hash) {
+		if (fd == fd2) {
+			LIST_REMOVE(fd, fd_hash);
+			break;
+		}
+	}
+	mtx_unlock(&fdesc_hashmtx);
+}
+
 int
-fdesc_allocvp(ftype, ix, mp, vpp, td)
+fdesc_allocvp(ftype, fd_fd, ix, mp, vpp, td)
 	fdntype ftype;
+	unsigned fd_fd;
 	int ix;
 	struct mount *mp;
 	struct vnode **vpp;
 	struct thread *td;
 {
+	struct fdescmount *fmp;
 	struct fdhashhead *fc;
-	struct fdescnode *fd;
+	struct fdescnode *fd, *fd2;
+	struct vnode *vp, *vp2;
 	int error = 0;
 
 	fc = FD_NHASH(ix);
 loop:
+	mtx_lock(&fdesc_hashmtx);
+	/*
+	 * If a forced unmount is progressing, we need to drop it. The flags are
+	 * protected by the hashmtx.
+	 */
+	fmp = (struct fdescmount *)mp->mnt_data;
+	if (fmp == NULL || fmp->flags & FMNT_UNMOUNTF) {
+		mtx_unlock(&fdesc_hashmtx);
+		return (-1);
+	}
+
 	LIST_FOREACH(fd, fc, fd_hash) {
 		if (fd->fd_ix == ix && fd->fd_vnode->v_mount == mp) {
-			if (vget(fd->fd_vnode, LK_EXCLUSIVE | LK_CANRECURSE,
-			    td))
+			/* Get reference to vnode in case it's being free'd */
+			vp = fd->fd_vnode;
+			VI_LOCK(vp);
+			mtx_unlock(&fdesc_hashmtx);
+			if (vget(vp, LK_EXCLUSIVE | LK_INTERLOCK, td))
 				goto loop;
-			*vpp = fd->fd_vnode;
-			VOP_UNLOCK(*vpp, 0);
-			return (error);
+			*vpp = vp;
+			return (0);
 		}
 	}
+	mtx_unlock(&fdesc_hashmtx);
 
-	/*
-	 * otherwise lock the array while we call getnewvnode
-	 * since that can block.
-	 */
-	if (fdcache_lock & FDL_LOCKED) {
-		fdcache_lock |= FDL_WANT;
-		(void) tsleep( &fdcache_lock, PINOD, "fdalvp", 0);
-		goto loop;
-	}
-	fdcache_lock |= FDL_LOCKED;
-
-	/*
-	 * Do the MALLOC before the getnewvnode since doing so afterward
-	 * might cause a bogus v_data pointer to get dereferenced
-	 * elsewhere if MALLOC should block.
-	 */
 	MALLOC(fd, struct fdescnode *, sizeof(struct fdescnode), M_TEMP, M_WAITOK);
 
-	error = getnewvnode("fdescfs", mp, &fdesc_vnodeops, vpp);
+	error = getnewvnode("fdescfs", mp, &fdesc_vnodeops, &vp);
 	if (error) {
 		FREE(fd, M_TEMP);
-		goto out;
+		return (error);
 	}
-	(*vpp)->v_data = fd;
-	fd->fd_vnode = *vpp;
+	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+	vp->v_data = fd;
+	fd->fd_vnode = vp;
 	fd->fd_type = ftype;
-	fd->fd_fd = -1;
+	fd->fd_fd = fd_fd;
 	fd->fd_ix = ix;
-	/* XXX: vnode should be locked here */
-	error = insmntque(*vpp, mp); /* XXX: Too early for mpsafe fs */
+	error = insmntque1(vp, mp, fdesc_insmntque_dtr, NULL);
 	if (error != 0) {
-		free(fd, M_TEMP);
 		*vpp = NULLVP;
-		goto out;
+		return (error);
 	}
-	LIST_INSERT_HEAD(fc, fd, fd_hash);
 
-out:
-	fdcache_lock &= ~FDL_LOCKED;
+	/* Make sure that someone didn't beat us when inserting the vnode. */
+	mtx_lock(&fdesc_hashmtx);
+	/*
+	 * If a forced unmount is progressing, we need to drop it. The flags are
+	 * protected by the hashmtx.
+	 */
+	fmp = (struct fdescmount *)mp->mnt_data;
+	if (fmp == NULL || fmp->flags & FMNT_UNMOUNTF) {
+		mtx_unlock(&fdesc_hashmtx);
+		vgone(vp);
+		vput(vp);
+		*vpp = NULLVP;
+		return (-1);
+	}
 
-	if (fdcache_lock & FDL_WANT) {
-		fdcache_lock &= ~FDL_WANT;
-		wakeup( &fdcache_lock);
+	LIST_FOREACH(fd2, fc, fd_hash) {
+		if (fd2->fd_ix == ix && fd2->fd_vnode->v_mount == mp) {
+			/* Get reference to vnode in case it's being free'd */
+			vp2 = fd2->fd_vnode;
+			VI_LOCK(vp2);
+			mtx_unlock(&fdesc_hashmtx);
+			error = vget(vp2, LK_EXCLUSIVE | LK_INTERLOCK, td);
+			/* Someone beat us, dec use count and wait for reclaim */
+			vgone(vp);
+			vput(vp);
+			/* If we didn't get it, return no vnode. */
+			if (error)
+				vp2 = NULLVP;
+			*vpp = vp2;
+			return (error);
+		}
 	}
 
-	return (error);
+	/* If we came here, we can insert it safely. */
+	LIST_INSERT_HEAD(fc, fd, fd_hash);
+	mtx_unlock(&fdesc_hashmtx);
+	*vpp = vp;
+	return (0);
 }
 
 /*
@@ -230,13 +302,43 @@ fdesc_lookup(ap)
 	if ((error = fget(td, fd, &fp)) != 0)
 		goto bad;
 
-	error = fdesc_allocvp(Fdesc, FD_DESC+fd, dvp->v_mount, &fvp, td);
-	fdrop(fp, td);
+	/* Check if we're looking up ourselves. */
+	if (VTOFDESC(dvp)->fd_ix == FD_DESC + fd) {
+		/*
+		 * In case we're holding the last reference to the file, the dvp
+		 * will be re-acquired.
+		 */
+		vhold(dvp);
+		VOP_UNLOCK(dvp, 0);
+		fdrop(fp, td);
+
+		/* Re-aquire the lock afterwards. */
+		vn_lock(dvp, LK_RETRY | LK_EXCLUSIVE);
+		vdrop(dvp);
+		fvp = dvp;
+	} else {
+		/*
+		 * Unlock our root node (dvp) when doing this, since we might
+		 * deadlock since the vnode might be locked by another thread
+		 * and the root vnode lock will be obtained afterwards (in case
+		 * we're looking up the fd of the root vnode), which will be the
+		 * opposite lock order. Vhold the root vnode first so we don't
+		 * loose it.
+		 */
+		vhold(dvp);
+		VOP_UNLOCK(dvp, 0);
+		error = fdesc_allocvp(Fdesc, fd, FD_DESC + fd, dvp->v_mount,
+		    &fvp, td);
+		fdrop(fp, td);
+		/*
+		 * The root vnode must be locked last to prevent deadlock condition.
+		 */
+		vn_lock(dvp, LK_RETRY | LK_EXCLUSIVE);
+		vdrop(dvp);
+	}
+	
 	if (error)
 		goto bad;
-	VTOFDESC(fvp)->fd_fd = fd;
-	if (fvp != dvp)
-		vn_lock(fvp, LK_EXCLUSIVE | LK_RETRY);
 	*vpp = fvp;
 	return (0);
 
@@ -505,34 +607,18 @@ done:
 }
 
 static int
-fdesc_inactive(ap)
-	struct vop_inactive_args /* {
-		struct vnode *a_vp;
-		struct thread *a_td;
-	} */ *ap;
-{
-	struct vnode *vp = ap->a_vp;
-
-	/*
-	 * Clear out the v_type field to avoid
-	 * nasty things happening in vgone().
-	 */
-	vp->v_type = VNON;
-	return (0);
-}
-
-static int
 fdesc_reclaim(ap)
 	struct vop_reclaim_args /* {
 		struct vnode *a_vp;
 	} */ *ap;
 {
-	struct vnode *vp = ap->a_vp;
-	struct fdescnode *fd = VTOFDESC(vp);
+	struct vnode *vp;
+	struct fdescnode *fd;
 
-	LIST_REMOVE(fd, fd_hash);
+ 	vp = ap->a_vp;
+ 	fd = VTOFDESC(vp);
+	fdesc_remove_entry(fd);
 	FREE(vp->v_data, M_TEMP);
-	vp->v_data = 0;
-
+	vp->v_data = NULL;
 	return (0);
 }