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Index: sys/fs/tmpfs/tmpfs_vfsops.c
===================================================================
--- sys/fs/tmpfs/tmpfs_vfsops.c
+++ sys/fs/tmpfs/tmpfs_vfsops.c
@@ -710,7 +710,8 @@
struct vfsops tmpfs_vfsops = {
.vfs_mount = tmpfs_mount,
.vfs_unmount = tmpfs_unmount,
- .vfs_root = tmpfs_root,
+ .vfs_root = vfs_cache_root,
+ .vfs_cachedroot = tmpfs_root,
.vfs_statfs = tmpfs_statfs,
.vfs_fhtovp = tmpfs_fhtovp,
.vfs_sync = tmpfs_sync,
Index: sys/kern/vfs_mount.c
===================================================================
--- sys/kern/vfs_mount.c
+++ sys/kern/vfs_mount.c
@@ -134,6 +134,7 @@
M_WAITOK | M_ZERO);
mp->mnt_ref = 0;
mp->mnt_vfs_ops = 1;
+ mp->mnt_rootvnode = NULL;
return (0);
}
@@ -582,6 +583,10 @@
panic("%s: vfs_ops should be 1 but %d found\n", __func__,
mp->mnt_vfs_ops);
+ if (mp->mnt_rootvnode != NULL)
+ panic("%s: mount point still has a root vnode %p\n", __func__,
+ mp->mnt_rootvnode);
+
if (mp->mnt_vnodecovered != NULL)
vrele(mp->mnt_vnodecovered);
#ifdef MAC
@@ -1010,6 +1015,7 @@
)
{
struct export_args export;
+ struct vnode *rootvp;
void *bufp;
struct mount *mp;
int error, export_error, len;
@@ -1075,7 +1081,10 @@
MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);
if ((mp->mnt_flag & MNT_ASYNC) == 0)
mp->mnt_kern_flag &= ~MNTK_ASYNC;
+ rootvp = vfs_cache_root_clear(mp);
MNT_IUNLOCK(mp);
+ if (rootvp != NULL)
+ vrele(rootvp);
mp->mnt_optnew = *optlist;
vfs_mergeopts(mp->mnt_optnew, mp->mnt_opt);
@@ -1553,7 +1562,7 @@
int
dounmount(struct mount *mp, int flags, struct thread *td)
{
- struct vnode *coveredvp;
+ struct vnode *coveredvp, *rootvp;
int error;
uint64_t async_flag;
int mnt_gen_r;
@@ -1601,12 +1610,15 @@
return (EBUSY);
}
mp->mnt_kern_flag |= MNTK_UNMOUNT;
+ rootvp = vfs_cache_root_clear(mp);
if (flags & MNT_NONBUSY) {
MNT_IUNLOCK(mp);
error = vfs_check_usecounts(mp);
MNT_ILOCK(mp);
if (error != 0) {
dounmount_cleanup(mp, coveredvp, MNTK_UNMOUNT);
+ if (rootvp != NULL)
+ vrele(rootvp);
return (error);
}
}
@@ -1635,6 +1647,9 @@
("%s: invalid return value for msleep in the drain path @ %s:%d",
__func__, __FILE__, __LINE__));
+ if (rootvp != NULL)
+ vrele(rootvp);
+
if (mp->mnt_flag & MNT_EXPUBLIC)
vfs_setpublicfs(NULL, NULL, NULL);
Index: sys/kern/vfs_subr.c
===================================================================
--- sys/kern/vfs_subr.c
+++ sys/kern/vfs_subr.c
@@ -5629,6 +5629,99 @@
return (0);
}
+/*
+ * Clear out a doomed vnode (if any) and replace it with a new one as long
+ * as the fs is not being unmounted. Return the root vnode to the caller.
+ */
+static int __noinline
+vfs_cache_root_fallback(struct mount *mp, int flags, struct vnode **vpp)
+{
+ struct vnode *vp;
+ int error;
+
+restart:
+ if (mp->mnt_rootvnode != NULL) {
+ MNT_ILOCK(mp);
+ vp = mp->mnt_rootvnode;
+ if (vp != NULL) {
+ if ((vp->v_iflag & VI_DOOMED) == 0) {
+ vrefact(vp);
+ MNT_IUNLOCK(mp);
+ error = vn_lock(vp, flags);
+ if (error == 0) {
+ *vpp = vp;
+ return (0);
+ }
+ vrele(vp);
+ goto restart;
+ }
+ /*
+ * Clear the old one.
+ */
+ mp->mnt_rootvnode = NULL;
+ }
+ MNT_IUNLOCK(mp);
+ if (vp != NULL) {
+ /*
+ * Paired with a fence in vfs_op_thread_exit().
+ */
+ atomic_thread_fence_acq();
+ vfs_op_barrier_wait(mp);
+ vrele(vp);
+ }
+ }
+ error = VFS_CACHEDROOT(mp, flags, vpp);
+ if (error != 0)
+ return (error);
+ if (mp->mnt_vfs_ops == 0) {
+ MNT_ILOCK(mp);
+ if (mp->mnt_rootvnode == NULL && mp->mnt_vfs_ops == 0) {
+ vrefact(*vpp);
+ mp->mnt_rootvnode = *vpp;
+ }
+ MNT_IUNLOCK(mp);
+ }
+ return (error);
+}
+
+int
+vfs_cache_root(struct mount *mp, int flags, struct vnode **vpp)
+{
+ struct vnode *vp;
+ int error;
+
+ if (!vfs_op_thread_enter(mp))
+ return (vfs_cache_root_fallback(mp, flags, vpp));
+ vp = (struct vnode *)atomic_load_ptr(&mp->mnt_rootvnode);
+ if (vp == NULL || (vp->v_iflag & VI_DOOMED)) {
+ vfs_op_thread_exit(mp);
+ return (vfs_cache_root_fallback(mp, flags, vpp));
+ }
+ vrefact(vp);
+ vfs_op_thread_exit(mp);
+ error = vn_lock(vp, flags);
+ if (error != 0) {
+ vrele(vp);
+ return (vfs_cache_root_fallback(mp, flags, vpp));
+ }
+ *vpp = vp;
+ return (0);
+}
+
+struct vnode *
+vfs_cache_root_clear(struct mount *mp)
+{
+ struct vnode *vp;
+
+ /*
+ * ops > 0 guarantees there is nobody who can see this vnode
+ */
+ MPASS(mp->mnt_vfs_ops > 0);
+ vp = mp->mnt_rootvnode;
+ mp->mnt_rootvnode = NULL;
+ return (vp);
+}
+
/*
* These are helper functions for filesystems to traverse all
* their vnodes. See MNT_VNODE_FOREACH_ALL() in sys/mount.h.
Index: sys/sys/mount.h
===================================================================
--- sys/sys/mount.h
+++ sys/sys/mount.h
@@ -231,6 +231,7 @@
int *mnt_ref_pcpu;
int *mnt_lockref_pcpu;
int *mnt_writeopcount_pcpu;
+ struct vnode *mnt_rootvnode;
};
/*
@@ -700,6 +701,7 @@
vfs_cmount_t *vfs_cmount;
vfs_unmount_t *vfs_unmount;
vfs_root_t *vfs_root;
+ vfs_root_t *vfs_cachedroot;
vfs_quotactl_t *vfs_quotactl;
vfs_statfs_t *vfs_statfs;
vfs_sync_t *vfs_sync;
@@ -739,6 +741,12 @@
_rc = (*(MP)->mnt_op->vfs_root)(MP, FLAGS, VPP); \
_rc; })
+#define VFS_CACHEDROOT(MP, FLAGS, VPP) ({ \
+ int _rc; \
+ \
+ _rc = (*(MP)->mnt_op->vfs_cachedroot)(MP, FLAGS, VPP); \
+ _rc; })
+
#define VFS_QUOTACTL(MP, C, U, A) ({ \
int _rc; \
\
@@ -948,6 +956,8 @@
void syncer_suspend(void);
void syncer_resume(void);
+struct vnode *vfs_cache_root_clear(struct mount *);
+
void vfs_op_barrier_wait(struct mount *);
void vfs_op_enter(struct mount *);
void vfs_op_exit_locked(struct mount *);
Index: sys/sys/vnode.h
===================================================================
--- sys/sys/vnode.h
+++ sys/sys/vnode.h
@@ -746,6 +746,7 @@
rangelock_trywlock(&(vp)->v_rl, (start), (end), VI_MTX(vp))
int vfs_cache_lookup(struct vop_lookup_args *ap);
+int vfs_cache_root(struct mount *mp, int flags, struct vnode **vpp);
void vfs_timestamp(struct timespec *);
void vfs_write_resume(struct mount *mp, int flags);
int vfs_write_suspend(struct mount *mp, int flags);
Index: sys/ufs/ffs/ffs_vfsops.c
===================================================================
--- sys/ufs/ffs/ffs_vfsops.c
+++ sys/ufs/ffs/ffs_vfsops.c
@@ -109,7 +109,8 @@
.vfs_mount = ffs_mount,
.vfs_cmount = ffs_cmount,
.vfs_quotactl = ufs_quotactl,
- .vfs_root = ufs_root,
+ .vfs_root = vfs_cache_root,
+ .vfs_cachedroot = ufs_root,
.vfs_statfs = ffs_statfs,
.vfs_sync = ffs_sync,
.vfs_uninit = ffs_uninit,

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