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diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -1075,79 +1075,6 @@
return (EEXIST);
}
-static int __noinline
-vfs_lookup_cross_mount(struct nameidata *ndp)
-{
- struct componentname *cnp;
- struct mount *mp;
- struct vnode *dp, *tdp;
- int error, crosslkflags;
- bool crosslock;
-
- cnp = &ndp->ni_cnd;
- dp = ndp->ni_vp;
-
- /*
- * The vnode has been mounted on, find the root of the mounted
- * filesystem.
- */
- for (;;) {
- mp = dp->v_mountedhere;
- ASSERT_VOP_LOCKED(dp, __func__);
- VNPASS((vn_irflag_read(dp) & VIRF_MOUNTPOINT) != 0 && mp != NULL, dp);
-
- crosslock = (dp->v_vflag & VV_CROSSLOCK) != 0;
- crosslkflags = enforce_lkflags(mp, cnp->cn_lkflags);
- if (__predict_false(crosslock)) {
- /*
- * We are going to be holding the vnode lock, which
- * in this case is shared by the root vnode of the
- * filesystem mounted at mp, across the call to
- * VFS_ROOT(). Make the situation clear to the
- * filesystem by passing LK_CANRECURSE if the
- * lock is held exclusive, or by clearinng
- * LK_NODDLKTREAT to allow recursion on the shared
- * lock in the presence of an exclusive waiter.
- */
- if (VOP_ISLOCKED(dp) == LK_EXCLUSIVE) {
- crosslkflags &= ~LK_SHARED;
- crosslkflags |= LK_EXCLUSIVE | LK_CANRECURSE;
- } else if ((crosslkflags & LK_EXCLUSIVE) != 0) {
- error = vn_lock(dp, LK_UPGRADE);
- if (error != 0)
- break;
- if (dp->v_mountedhere != mp) {
- continue;
- }
- } else
- crosslkflags &= ~LK_NODDLKTREAT;
- }
- if (vfs_busy(mp, 0) != 0)
- continue;
- if (__predict_true(!crosslock))
- vput(dp);
- if (dp != ndp->ni_dvp)
- vput(ndp->ni_dvp);
- else
- vrele(ndp->ni_dvp);
- vrefact(vp_crossmp);
- ndp->ni_dvp = vp_crossmp;
- error = VFS_ROOT(mp, crosslkflags, &tdp);
- vfs_unbusy(mp);
- if (__predict_false(crosslock))
- vput(dp);
- if (vn_lock(vp_crossmp, LK_SHARED | LK_NOWAIT))
- panic("vp_crossmp exclusively locked or reclaimed");
- if (error != 0)
- break;
- ndp->ni_vp = dp = tdp;
- if ((vn_irflag_read(dp) & VIRF_MOUNTPOINT) == 0)
- break;
- }
-
- return (error);
-}
-
/*
* Search a pathname.
* This is a very central and rather complicated routine.
@@ -1559,17 +1486,54 @@
goto success;
}
- if ((vn_irflag_read(dp) & VIRF_MOUNTPOINT) != 0 &&
- (cnp->cn_flags & NOCROSSMOUNT) == 0) {
- error = vfs_lookup_cross_mount(ndp);
- if (error != 0)
- goto bad_unlocked;
+ /* From here: Not a symlink we have to follow. */
+
+ /*
+ * Going to cross mounts, if any and if not ruled out.
+ */
+ if (__predict_true((vn_irflag_read(dp) & VIRF_MOUNTPOINT) == 0) ||
+ (cnp->cn_flags & NOCROSSMOUNT) != 0)
+ goto nextname;
+
+ /*
+ * Unlock the parent 'ni_dvp' to avoid a problem with NFS where
+ * VFS_ROOT() can hang forever on a lost server. In this case, 'ni_dvp'
+ * remains locked forever as well, gradually blocking all lookups (or
+ * only modifications in the MNTK_LOOKUP_SHARED case) starting with
+ * vnodes earlier in the path up to the root vnode.
+ */
+ if (ndp->ni_dvp != dp)
+ VOP_UNLOCK(ndp->ni_dvp);
+
+ error = vn_cross_mounts_mounted(dp, cnp->cn_lkflags, &dp);
+ if (__predict_false(error != 0)) {
+ vrele(ndp->ni_dvp);
/*
- * FALLTHROUGH to nextname
+ * If 'error' is ENOENT, during crossing, 'dp' was unlocked and
+ * is now doomed, which, given the pre-existing active
+ * reference, can only happen on a forced unmount. We could
+ * climb to the "parent" directory (in the resolution, i.e.,
+ * 'ni_dvp'), but this is likely to be useless (if on the same
+ * mount it can have been doomed already, and if not, it
+ * currently is equal to 'vp_crossmp' anyway) and problematic
+ * semantically if done standalone. The most sensible
+ * alternative would be to restart the whole resolution, but we
+ * are not there yet.
*/
- dp = ndp->ni_vp;
+ goto bad_unlocked;
}
+ /*
+ * We effectively crossed some mounts. Release 'ni_dvp', which
+ * is going to be replaced by 'vp_crossmp'.
+ */
+ ndp->ni_vp = dp;
+ vrele(ndp->ni_dvp);
+ vrefact(vp_crossmp);
+ if (vn_lock(vp_crossmp, LK_SHARED | LK_NOWAIT))
+ panic("vp_crossmp exclusively locked or reclaimed");
+ ndp->ni_dvp = vp_crossmp;
+
nextname:
/*
* Not a symbolic link that we will follow. Continue with the

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