Merge tag 'pull-mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs mount updates from Al Viro:

 - mount hash conflicts rudiments are gone now - we do not allow
     multiple mounts with the same parent/mountpoint to be hashed at the
     same time.

 - 'struct mount' changes:
      - mnt_umounting is gone
      - mnt_slave_list/mnt_slave is an hlist now
      - overmounts are kept track of by explicit pointer in mount
      - a bunch of flags moved out of mnt_flags to a new field, with
        only namespace_sem for protection
      - mnt_expiry is protected by mount_lock now (instead of
        namespace_sem)
      - MNT_LOCKED is used only for mounts that need to remain attached
        to their parents to prevent mountpoint exposure - no more
        overloading it for absolute roots
      - all mnt_list uses are transient now - it's used only to
        represent temporary sets during umount_tree()

 - mount refcounting change: children no longer pin parents for any
   mounts, whether they'd passed through umount_tree() or not

 - 'struct mountpoint' changes:
      - refcount is no more; what matters is ->m_list emptiness
      - instead of temporary bumping the refcount, we insert a new
        object (pinned_mountpoint) into ->m_list
      - new calling conventions for lock_mount() and friends

 - do_move_mount()/attach_recursive_mnt() seriously cleaned up

 - globals in fs/pnode.c are gone

 - propagate_mnt(), change_mnt_propagation() and propagate_umount()
   cleaned up (in the last case - pretty much completely rewritten).

 - freeing of emptied mnt_namespace is done in namespace_unlock(). For
   one thing, there are subtle ordering requirements there; for another
   it simplifies cleanups.

 - assorted cleanups

 - restore the machinery for long-term mounts from accumulated bitrot.

   This is going to get a followup come next cycle, when the change of
   vfs_fs_parse_string() calling conventions goes into -next

* tag 'pull-mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (48 commits)
  statmount_mnt_basic(): simplify the logics for group id
  invent_group_ids(): zero ->mnt_group_id always implies !IS_MNT_SHARED()
  get rid of CL_SHARE_TO_SLAVE
  take freeing of emptied mnt_namespace to namespace_unlock()
  copy_tree(): don't link the mounts via mnt_list
  change_mnt_propagation(): move ->mnt_master assignment into MS_SLAVE case
  mnt_slave_list/mnt_slave: turn into hlist_head/hlist_node
  turn do_make_slave() into transfer_propagation()
  do_make_slave(): choose new master sanely
  change_mnt_propagation(): do_make_slave() is a no-op unless IS_MNT_SHARED()
  change_mnt_propagation() cleanups, step 1
  propagate_mnt(): fix comment and convert to kernel-doc, while we are at it
  propagate_mnt(): get rid of last_dest
  fs/pnode.c: get rid of globals
  propagate_one(): fold into the sole caller
  propagate_one(): separate the "what should be the master for this copy" part
  propagate_one(): separate the "do we need secondary here?" logics
  propagate_mnt(): handle all peer groups in the same loop
  propagate_one(): get rid of dest_master
  mount: separate the flags accessed only under namespace_sem
  ...

Documentation/filesystems/propagate_umount.txt

@@ -0,0 +1,484 @@
+	Notes on propagate_umount()
+
+Umount propagation starts with a set of mounts we are already going to
+take out.  Ideally, we would like to add all downstream cognates to
+that set - anything with the same mountpoint as one of the removed
+mounts and with parent that would receive events from the parent of that
+mount.  However, there are some constraints the resulting set must
+satisfy.
+
+It is convenient to define several properties of sets of mounts:
+
+1) A set S of mounts is non-shifting if for any mount X belonging
+to S all subtrees mounted strictly inside of X (i.e. not overmounting
+the root of X) contain only elements of S.
+
+2) A set S is non-revealing if all locked mounts that belong to S have
+parents that also belong to S.
+
+3) A set S is closed if it contains all children of its elements.
+
+The set of mounts taken out by umount(2) must be non-shifting and
+non-revealing; the first constraint is what allows to reparent
+any remaining mounts and the second is what prevents the exposure
+of any concealed mountpoints.
+
+propagate_umount() takes the original set as an argument and tries to
+extend that set.  The original set is a full subtree and its root is
+unlocked; what matters is that it's closed and non-revealing.
+Resulting set may not be closed; there might still be mounts outside
+of that set, but only on top of stacks of root-overmounting elements
+of set.  They can be reparented to the place where the bottom of
+stack is attached to a mount that will survive.  NOTE: doing that
+will violate a constraint on having no more than one mount with
+the same parent/mountpoint pair; however, the caller (umount_tree())
+will immediately remedy that - it may keep unmounted element attached
+to parent, but only if the parent itself is unmounted.  Since all
+conflicts created by reparenting have common parent *not* in the
+set and one side of the conflict (bottom of the stack of overmounts)
+is in the set, it will be resolved.  However, we rely upon umount_tree()
+doing that pretty much immediately after the call of propagate_umount().
+
+Algorithm is based on two statements:
+	1) for any set S, there is a maximal non-shifting subset of S
+and it can be calculated in O(#S) time.
+	2) for any non-shifting set S, there is a maximal non-revealing
+subset of S.  That subset is also non-shifting and it can be calculated
+in O(#S) time.
+
+		Finding candidates.
+
+We are given a closed set U and we want to find all mounts that have
+the same mountpoint as some mount m in U *and* whose parent receives
+propagation from the parent of the same mount m.  Naive implementation
+would be
+	S = {}
+	for each m in U
+		add m to S
+		p = parent(m)
+		for each q in Propagation(p) - {p}
+			child = look_up(q, mountpoint(m))
+			if child
+				add child to S
+but that can lead to excessive work - there might be propagation among the
+subtrees of U, in which case we'd end up examining the same candidates
+many times.  Since propagation is transitive, the same will happen to
+everything downstream of that candidate and it's not hard to construct
+cases where the approach above leads to the time quadratic by the actual
+number of candidates.
+
+Note that if we run into a candidate we'd already seen, it must've been
+added on an earlier iteration of the outer loop - all additions made
+during one iteration of the outer loop have different parents.  So
+if we find a child already added to the set, we know that everything
+in Propagation(parent(child)) with the same mountpoint has been already
+added.
+	S = {}
+	for each m in U
+		if m in S
+			continue
+		add m to S
+		p = parent(m)
+		q = propagation_next(p, p)
+		while q
+			child = look_up(q, mountpoint(m))
+			if child
+				if child in S
+					q = skip_them(q, p)
+					continue;
+				add child to S
+			q = propagation_next(q, p)
+where
+skip_them(q, p)
+	keep walking Propagation(p) from q until we find something
+	not in Propagation(q)
+
+would get rid of that problem, but we need a sane implementation of
+skip_them().  That's not hard to do - split propagation_next() into
+"down into mnt_slave_list" and "forward-and-up" parts, with the
+skip_them() being "repeat the forward-and-up part until we get NULL
+or something that isn't a peer of the one we are skipping".
+
+Note that there can be no absolute roots among the extra candidates -
+they all come from mount lookups.  Absolute root among the original
+set is _currently_ impossible, but it might be worth protecting
+against.
+
+		Maximal non-shifting subsets.
+
+Let's call a mount m in a set S forbidden in that set if there is a
+subtree mounted strictly inside m and containing mounts that do not
+belong to S.
+
+The set is non-shifting when none of its elements are forbidden in it.
+
+If mount m is forbidden in a set S, it is forbidden in any subset S' it
+belongs to.  In other words, it can't belong to any of the non-shifting
+subsets of S.  If we had a way to find a forbidden mount or show that
+there's none, we could use it to find the maximal non-shifting subset
+simply by finding and removing them until none remain.
+
+Suppose mount m is forbidden in S; then any mounts forbidden in S - {m}
+must have been forbidden in S itself.  Indeed, since m has descendents
+that do not belong to S, any subtree that fits into S will fit into
+S - {m} as well.
+
+So in principle we could go through elements of S, checking if they
+are forbidden in S and removing the ones that are.  Removals will
+not invalidate the checks done for earlier mounts - if they were not
+forbidden at the time we checked, they won't become forbidden later.
+It's too costly to be practical, but there is a similar approach that
+is linear by size of S.
+
+Let's say that mount x in a set S is forbidden by mount y, if
+	* both x and y belong to S.
+	* there is a chain of mounts starting at x and leaving S
+	  immediately after passing through y, with the first
+	  mountpoint strictly inside x.
+Note 1: x may be equal to y - that's the case when something not
+belonging to S is mounted strictly inside x.
+Note 2: if y does not belong to S, it can't forbid anything in S.
+Note 3: if y has no children outside of S, it can't forbid anything in S.
+
+It's easy to show that mount x is forbidden in S if and only if x is
+forbidden in S by some mount y.  And it's easy to find all mounts in S
+forbidden by a given mount.
+
+Consider the following operation:
+	Trim(S, m) = S - {x : x is forbidden by m in S}
+
+Note that if m does not belong to S or has no children outside of S we
+are guaranteed that Trim(S, m) is equal to S.
+
+The following is true: if x is forbidden by y in Trim(S, m), it was
+already forbidden by y in S.
+
+Proof: Suppose x is forbidden by y in Trim(S, m).  Then there is a
+chain of mounts (x_0 = x, ..., x_k = y, x_{k+1} = r), such that x_{k+1}
+is the first element that doesn't belong to Trim(S, m) and the
+mountpoint of x_1 is strictly inside x.  If mount r belongs to S, it must
+have been removed by Trim(S, m), i.e. it was forbidden in S by m.
+Then there was a mount chain from r to some child of m that stayed in
+S all the way until m, but that's impossible since x belongs to Trim(S, m)
+and prepending (x_0, ..., x_k) to that chain demonstrates that x is also
+forbidden in S by m, and thus can't belong to Trim(S, m).
+Therefore r can not belong to S and our chain demonstrates that
+x is forbidden by y in S.  QED.
+
+Corollary: no mount is forbidden by m in Trim(S, m).  Indeed, any
+such mount would have been forbidden by m in S and thus would have been
+in the part of S removed in Trim(S, m).
+
+Corollary: no mount is forbidden by m in Trim(Trim(S, m), n).  Indeed,
+any such would have to have been forbidden by m in Trim(S, m), which
+is impossible.
+
+Corollary: after
+	S = Trim(S, x_1)
+	S = Trim(S, x_2)
+	...
+	S = Trim(S, x_k)
+no mount remaining in S will be forbidden by either of x_1,...,x_k.
+
+The following will reduce S to its maximal non-shifting subset:
+	visited = {}
+	while S contains elements not belonging to visited
+		let m be an arbitrary such element of S
+		S = Trim(S, m)
+		add m to visited
+
+S never grows, so the number of elements of S not belonging to visited
+decreases at least by one on each iteration.  When the loop terminates,
+all mounts remaining in S belong to visited.  It's easy to see that at
+the beginning of each iteration no mount remaining in S will be forbidden
+by any element of visited.  In other words, no mount remaining in S will
+be forbidden, i.e. final value of S will be non-shifting.  It will be
+the maximal non-shifting subset, since we were removing only forbidden
+elements.
+
+	There are two difficulties in implementing the above in linear
+time, both due to the fact that Trim() might need to remove more than one
+element.  Naive implementation of Trim() is vulnerable to running into a
+long chain of mounts, each mounted on top of parent's root.  Nothing in
+that chain is forbidden, so nothing gets removed from it.  We need to
+recognize such chains and avoid walking them again on subsequent calls of
+Trim(), otherwise we will end up with worst-case time being quadratic by
+the number of elements in S.  Another difficulty is in implementing the
+outer loop - we need to iterate through all elements of a shrinking set.
+That would be trivial if we never removed more than one element at a time
+(linked list, with list_for_each_entry_safe for iterator), but we may
+need to remove more than one entry, possibly including the ones we have
+already visited.
+
+	Let's start with naive algorithm for Trim():
+
+Trim_one(m)
+	found = false
+	for each n in children(m)
+		if n not in S
+			found = true
+			if (mountpoint(n) != root(m))
+				remove m from S
+				break
+	if found
+		Trim_ancestors(m)
+
+Trim_ancestors(m)
+	for (; parent(m) in S; m = parent(m)) {
+		if (mountpoint(m) != root(parent(m)))
+			remove parent(m) from S
+	}
+
+If m belongs to S, Trim_one(m) will replace S with Trim(S, m).
+Proof:
+	Consider the chains excluding elements from Trim(S, m).  The last
+two elements in such chain are m and some child of m that does not belong
+to S.  If m has no such children, Trim(S, m) is equal to S.
+	m itself is removed if and only if the chain has exactly two
+elements, i.e. when the last element does not overmount the root of m.
+In other words, that happens when m has a child not in S that does not
+overmount the root of m.
+	All other elements to remove will be ancestors of m, such that
+the entire descent chain from them to m is contained in S.  Let
+(x_0, x_1, ..., x_k = m) be the longest such chain.  x_i needs to be
+removed if and only if x_{i+1} does not overmount its root.  It's easy
+to see that Trim_ancestors(m) will iterate through that chain from
+x_k to x_1 and that it will remove exactly the elements that need to be
+removed.
+
+	Note that if the loop in Trim_ancestors() walks into an already
+visited element, we are guaranteed that remaining iterations will see
+only elements that had already been visited and remove none of them.
+That's the weakness that makes it vulnerable to long chains of full
+overmounts.
+
+	It's easy to deal with, if we can afford setting marks on
+elements of S; we would mark all elements already visited by
+Trim_ancestors() and have it bail out as soon as it sees an already
+marked element.
+
+	The problems with iterating through the set can be dealt with in
+several ways, depending upon the representation we choose for our set.
+One useful observation is that we are given a closed subset in S - the
+original set passed to propagate_umount().  Its elements can neither
+forbid anything nor be forbidden by anything - all their descendents
+belong to S, so they can not occur anywhere in any excluding chain.
+In other words, the elements of that subset will remain in S until
+the end and Trim_one(S, m) is a no-op for all m from that subset.
+
+	That suggests keeping S as a disjoint union of a closed set U
+('will be unmounted, no matter what') and the set of all elements of
+S that do not belong to U.  That set ('candidates') is all we need
+to iterate through.  Let's represent it as a subset in a cyclic list,
+consisting of all list elements that are marked as candidates (initially -
+all of them).  Then we could have Trim_ancestors() only remove the mark,
+leaving the elements on the list.  Then Trim_one() would never remove
+anything other than its argument from the containing list, allowing to
+use list_for_each_entry_safe() as iterator.
+
+	Assuming that representation we get the following:
+
+	list_for_each_entry_safe(m, ..., Candidates, ...)
+		Trim_one(m)
+where
+Trim_one(m)
+	if (m is not marked as a candidate)
+		strip the "seen by Trim_ancestors" mark from m
+		remove m from the Candidates list
+		return
+		
+	remove_this = false
+	found = false
+	for each n in children(m)
+		if n not in S
+			found = true
+			if (mountpoint(n) != root(m))
+				remove_this = true
+				break
+	if found
+		Trim_ancestors(m)
+	if remove_this
+		strip the "seen by Trim_ancestors" mark from m
+		strip the "candidate" mark from m
+		remove m from the Candidate list
+
+Trim_ancestors(m)
+	for (p = parent(m); p is marked as candidate ; m = p, p = parent(p)) {
+		if m is marked as seen by Trim_ancestors
+			return
+		mark m as seen by Trim_ancestors
+		if (mountpoint(m) != root(p))
+			strip the "candidate" mark from p
+	}
+
+	Terminating condition in the loop in Trim_ancestors() is correct,
+since that that loop will never run into p belonging to U - p is always
+an ancestor of argument of Trim_one() and since U is closed, the argument
+of Trim_one() would also have to belong to U.  But Trim_one() is never
+called for elements of U.  In other words, p belongs to S if and only
+if it belongs to candidates.
+
+	Time complexity:
+* we get no more than O(#S) calls of Trim_one()
+* the loop over children in Trim_one() never looks at the same child
+twice through all the calls.
+* iterations of that loop for children in S are no more than O(#S)
+in the worst case
+* at most two children that are not elements of S are considered per
+call of Trim_one().
+* the loop in Trim_ancestors() sets its mark once per iteration and
+no element of S has is set more than once.
+
+	In the end we may have some elements excluded from S by
+Trim_ancestors() still stuck on the list.  We could do a separate
+loop removing them from the list (also no worse than O(#S) time),
+but it's easier to leave that until the next phase - there we will
+iterate through the candidates anyway.
+
+	The caller has already removed all elements of U from their parents'
+lists of children, which means that checking if child belongs to S is
+equivalent to checking if it's marked as a candidate; we'll never see
+the elements of U in the loop over children in Trim_one().
+
+	What's more, if we see that children(m) is empty and m is not
+locked, we can immediately move m into the committed subset (remove
+from the parent's list of children, etc.).  That's one fewer mount we'll
+have to look into when we check the list of children of its parent *and*
+when we get to building the non-revealing subset.
+
+		Maximal non-revealing subsets
+
+If S is not a non-revealing subset, there is a locked element x in S
+such that parent of x is not in S.
+
+Obviously, no non-revealing subset of S may contain x.  Removing such
+elements one by one will obviously end with the maximal non-revealing
+subset (possibly empty one).  Note that removal of an element will
+require removal of all its locked children, etc.
+
+If the set had been non-shifting, it will remain non-shifting after
+such removals.
+Proof: suppose S was non-shifting, x is a locked element of S, parent of x
+is not in S and S - {x} is not non-shifting.  Then there is an element m
+in S - {x} and a subtree mounted strictly inside m, such that m contains
+an element not in in S - {x}.  Since S is non-shifting, everything in
+that subtree must belong to S.  But that means that this subtree must
+contain x somewhere *and* that parent of x either belongs that subtree
+or is equal to m.  Either way it must belong to S.  Contradiction.
+
+// same representation as for finding maximal non-shifting subsets:
+// S is a disjoint union of a non-revealing set U (the ones we are committed
+// to unmount) and a set of candidates, represented as a subset of list
+// elements that have "is a candidate" mark on them.
+// Elements of U are removed from their parents' lists of children.
+// In the end candidates becomes empty and maximal non-revealing non-shifting
+// subset of S is now in U
+	while (Candidates list is non-empty)
+		handle_locked(first(Candidates))
+
+handle_locked(m)
+	if m is not marked as a candidate
+		strip the "seen by Trim_ancestors" mark from m
+		remove m from the list
+		return
+	cutoff = m
+	for (p = m; p in candidates; p = parent(p)) {
+		strip the "seen by Trim_ancestors" mark from p
+		strip the "candidate" mark from p
+		remove p from the Candidates list
+		if (!locked(p))
+			cutoff = parent(p)
+	}
+	if p in U
+		cutoff = p
+	while m != cutoff
+		remove m from children(parent(m))
+		add m to U
+		m = parent(m)
+
+Let (x_0, ..., x_n = m) be the maximal chain of descent of m within S.
+* If it contains some elements of U, let x_k be the last one of those.
+Then union of U with {x_{k+1}, ..., x_n} is obviously non-revealing.
+* otherwise if all its elements are locked, then none of {x_0, ..., x_n}
+may be elements of a non-revealing subset of S.
+* otherwise let x_k be the first unlocked element of the chain.  Then none
+of {x_0, ..., x_{k-1}} may be an element of a non-revealing subset of
+S and union of U and {x_k, ..., x_n} is non-revealing.
+
+handle_locked(m) finds which of these cases applies and adjusts Candidates
+and U accordingly.  U remains non-revealing, union of Candidates and
+U still contains any non-revealing subset of S and after the call of
+handle_locked(m) m is guaranteed to be not in Candidates list.  So having
+it called for each element of S would suffice to empty Candidates,
+leaving U the maximal non-revealing subset of S.
+
+However, handle_locked(m) is a no-op when m belongs to U, so it's enough
+to have it called for elements of Candidates list until none remain.
+
+Time complexity: number of calls of handle_locked() is limited by
+#Candidates, each iteration of the first loop in handle_locked() removes
+an element from the list, so their total number of executions is also
+limited by #Candidates; number of iterations in the second loop is no
+greater than the number of iterations of the first loop.
+
+
+		Reparenting
+
+After we'd calculated the final set, we still need to deal with
+reparenting - if an element of the final set has a child not in it,
+we need to reparent such child.
+
+Such children can only be root-overmounting (otherwise the set wouldn't
+be non-shifting) and their parents can not belong to the original set,
+since the original is guaranteed to be closed.
+
+
+		Putting all of that together
+
+The plan is to
+	* find all candidates
+	* trim down to maximal non-shifting subset
+	* trim down to maximal non-revealing subset
+	* reparent anything that needs to be reparented
+	* return the resulting set to the caller
+
+For the 2nd and 3rd steps we want to separate the set into growing
+non-revealing subset, initially containing the original set ("U" in
+terms of the pseudocode above) and everything we are still not sure about
+("candidates").  It means that for the output of the 1st step we'd like
+the extra candidates separated from the stuff already in the original set.
+For the 4th step we would like the additions to U separate from the
+original set.
+
+So let's go for
+	* original set ("set").  Linkage via mnt_list
+	* undecided candidates ("candidates").  Subset of a list,
+consisting of all its elements marked with a new flag (T_UMOUNT_CANDIDATE).
+Initially all elements of the list will be marked that way; in the
+end the list will become empty and no mounts will remain marked with
+that flag.
+	* Reuse T_MARKED for "has been already seen by trim_ancestors()".
+	* anything in U that hadn't been in the original set - elements of
+candidates will gradually be either discarded or moved there.  In other
+words, it's the candidates we have already decided to unmount.	Its role
+is reasonably close to the old "to_umount", so let's use that name.
+Linkage via mnt_list.
+
+For gather_candidates() we'll need to maintain both candidates (S -
+set) and intersection of S with set.  Use T_UMOUNT_CANDIDATE for
+all elements we encounter, putting the ones not already in the original
+set into the list of candidates.  When we are done, strip that flag from
+all elements of the original set.  That gives a cheap way to check
+if element belongs to S (in gather_candidates) and to candidates
+itself (at later stages).  Call that predicate is_candidate(); it would
+be m->mnt_t_flags & T_UMOUNT_CANDIDATE.
+
+All elements of the original set are marked with MNT_UMOUNT and we'll
+need the same for elements added when joining the contents of to_umount
+to set in the end.  Let's set MNT_UMOUNT at the time we add an element
+to to_umount; that's close to what the old 'umount_one' is doing, so
+let's keep that name.  It also gives us another predicate we need -
+"belongs to union of set and to_umount"; will_be_unmounted() for now.
+
+Removals from the candidates list should strip both T_MARKED and
+T_UMOUNT_CANDIDATE; call it remove_from_candidates_list().

drivers/gpu/drm/i915/gem/i915_gemfs.c

@@ -5,16 +5,23 @@
 
 #include <linux/fs.h>
 #include <linux/mount.h>
+#include <linux/fs_context.h>
 
 #include "i915_drv.h"
 #include "i915_gemfs.h"
 #include "i915_utils.h"
 
+static int add_param(struct fs_context *fc, const char *key, const char *val)
+{
+	return vfs_parse_fs_string(fc, key, val, strlen(val));
+}
+
 void i915_gemfs_init(struct drm_i915_private *i915)
 {
-	char huge_opt[] = "huge=within_size"; /* r/w */
 	struct file_system_type *type;
+	struct fs_context *fc;
 	struct vfsmount *gemfs;
+	int ret;
 
 	/*
 	 * By creating our own shmemfs mountpoint, we can pass in
@@ -38,8 +45,16 @@ void i915_gemfs_init(struct drm_i915_private *i915)
 	if (!type)
 		goto err;
 
-	gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, huge_opt);
-	if (IS_ERR(gemfs))
+	fc = fs_context_for_mount(type, SB_KERNMOUNT);
+	if (IS_ERR(fc))
+		goto err;
+	ret = add_param(fc, "source", "tmpfs");
+	if (!ret)
+		ret = add_param(fc, "huge", "within_size");
+	if (!ret)
+		gemfs = fc_mount_longterm(fc);
+	put_fs_context(fc);
+	if (ret)
 		goto err;
 
 	i915->mm.gemfs = gemfs;

drivers/gpu/drm/v3d/v3d_gemfs.c

@@ -3,14 +3,21 @@
 
 #include <linux/fs.h>
 #include <linux/mount.h>
+#include <linux/fs_context.h>
 
 #include "v3d_drv.h"
 
+static int add_param(struct fs_context *fc, const char *key, const char *val)
+{
+	return vfs_parse_fs_string(fc, key, val, strlen(val));
+}
+
 void v3d_gemfs_init(struct v3d_dev *v3d)
 {
-	char huge_opt[] = "huge=within_size";
 	struct file_system_type *type;
+	struct fs_context *fc;
 	struct vfsmount *gemfs;
+	int ret;
 
 	/*
 	 * By creating our own shmemfs mountpoint, we can pass in
@@ -28,8 +35,16 @@ void v3d_gemfs_init(struct v3d_dev *v3d)
 	if (!type)
 		goto err;
 
-	gemfs = vfs_kern_mount(type, SB_KERNMOUNT, type->name, huge_opt);
-	if (IS_ERR(gemfs))
+	fc = fs_context_for_mount(type, SB_KERNMOUNT);
+	if (IS_ERR(fc))
+		goto err;
+	ret = add_param(fc, "source", "tmpfs");
+	if (!ret)
+		ret = add_param(fc, "huge", "within_size");
+	if (!ret)
+		gemfs = fc_mount_longterm(fc);
+	put_fs_context(fc);
+	if (ret)
 		goto err;
 
 	v3d->gemfs = gemfs;

fs/hugetlbfs/inode.c

@@ -1588,7 +1588,7 @@ static struct vfsmount *__init mount_one_hugetlbfs(struct hstate *h)
 	} else {
 		struct hugetlbfs_fs_context *ctx = fc->fs_private;
 		ctx->hstate = h;
-		mnt = fc_mount(fc);
+		mnt = fc_mount_longterm(fc);
 		put_fs_context(fc);
 	}
 	if (IS_ERR(mnt))

fs/mount.h

@@ -44,7 +44,6 @@ struct mountpoint {
 	struct hlist_node m_hash;
 	struct dentry *m_dentry;
 	struct hlist_head m_list;
-	int m_count;
 };
 
 struct mount {
@@ -70,8 +69,8 @@ struct mount {
 	struct list_head mnt_list;
 	struct list_head mnt_expire;	/* link in fs-specific expiry list */
 	struct list_head mnt_share;	/* circular list of shared mounts */
-	struct list_head mnt_slave_list;/* list of slave mounts */
-	struct list_head mnt_slave;	/* slave list entry */
+	struct hlist_head mnt_slave_list;/* list of slave mounts */
+	struct hlist_node mnt_slave;	/* slave list entry */
 	struct mount *mnt_master;	/* slave is on master->mnt_slave_list */
 	struct mnt_namespace *mnt_ns;	/* containing namespace */
 	struct mountpoint *mnt_mp;	/* where is it mounted */
@@ -79,21 +78,38 @@ struct mount {
 		struct hlist_node mnt_mp_list;	/* list mounts with the same mountpoint */
 		struct hlist_node mnt_umount;
 	};
-	struct list_head mnt_umounting; /* list entry for umount propagation */
 #ifdef CONFIG_FSNOTIFY
 	struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks;
 	__u32 mnt_fsnotify_mask;
 	struct list_head to_notify;	/* need to queue notification */
 	struct mnt_namespace *prev_ns;	/* previous namespace (NULL if none) */
 #endif
+	int mnt_t_flags;		/* namespace_sem-protected flags */
 	int mnt_id;			/* mount identifier, reused */
 	u64 mnt_id_unique;		/* mount ID unique until reboot */
 	int mnt_group_id;		/* peer group identifier */
 	int mnt_expiry_mark;		/* true if marked for expiry */
 	struct hlist_head mnt_pins;
 	struct hlist_head mnt_stuck_children;
+	struct mount *overmount;	/* mounted on ->mnt_root */
 } __randomize_layout;
 
+enum {
+	T_SHARED		= 1, /* mount is shared */
+	T_UNBINDABLE		= 2, /* mount is unbindable */
+	T_MARKED		= 4, /* internal mark for propagate_... */
+	T_UMOUNT_CANDIDATE	= 8, /* for propagate_umount */
+
+	/*
+	 * T_SHARED_MASK is the set of flags that should be cleared when a
+	 * mount becomes shared.  Currently, this is only the flag that says a
+	 * mount cannot be bind mounted, since this is how we create a mount
+	 * that shares events with another mount.  If you add a new T_*
+	 * flag, consider how it interacts with shared mounts.
+	 */
+	T_SHARED_MASK	= T_UNBINDABLE,
+};
+
 #define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
 
 static inline struct mount *real_mount(struct vfsmount *mnt)
@@ -101,7 +117,7 @@ static inline struct mount *real_mount(struct vfsmount *mnt)
 	return container_of(mnt, struct mount, mnt);
 }
 
-static inline int mnt_has_parent(struct mount *mnt)
+static inline int mnt_has_parent(const struct mount *mnt)
 {
 	return mnt != mnt->mnt_parent;
 }
@@ -146,8 +162,8 @@ struct proc_mounts {
 
 extern const struct seq_operations mounts_op;
 
-extern bool __is_local_mountpoint(struct dentry *dentry);
-static inline bool is_local_mountpoint(struct dentry *dentry)
+extern bool __is_local_mountpoint(const struct dentry *dentry);
+static inline bool is_local_mountpoint(const struct dentry *dentry)
 {
 	if (!d_mountpoint(dentry))
 		return false;
@@ -160,6 +176,13 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
 	return ns->seq == 0;
 }
 
+static inline bool anon_ns_root(const struct mount *m)
+{
+	struct mnt_namespace *ns = READ_ONCE(m->mnt_ns);
+
+	return !IS_ERR_OR_NULL(ns) && is_anon_ns(ns) && m == ns->root;
+}
+
 static inline bool mnt_ns_attached(const struct mount *mnt)
 {
 	return !RB_EMPTY_NODE(&mnt->mnt_node);
@@ -170,7 +193,7 @@ static inline bool mnt_ns_empty(const struct mnt_namespace *ns)
 	return RB_EMPTY_ROOT(&ns->mounts);
 }
 
-static inline void move_from_ns(struct mount *mnt, struct list_head *dt_list)
+static inline void move_from_ns(struct mount *mnt)
 {
 	struct mnt_namespace *ns = mnt->mnt_ns;
 	WARN_ON(!mnt_ns_attached(mnt));
@@ -180,7 +203,6 @@ static inline void move_from_ns(struct mount *mnt, struct list_head *dt_list)
 		ns->mnt_first_node = rb_next(&mnt->mnt_node);
 	rb_erase(&mnt->mnt_node, &ns->mounts);
 	RB_CLEAR_NODE(&mnt->mnt_node);
-	list_add_tail(&mnt->mnt_list, dt_list);
 }
 
 bool has_locked_children(struct mount *mnt, struct dentry *dentry);

fs/pnode.h

@@ -10,14 +10,14 @@
 #include <linux/list.h>
 #include "mount.h"
 
-#define IS_MNT_SHARED(m) ((m)->mnt.mnt_flags & MNT_SHARED)
+#define IS_MNT_SHARED(m) ((m)->mnt_t_flags & T_SHARED)
 #define IS_MNT_SLAVE(m) ((m)->mnt_master)
 #define IS_MNT_NEW(m) (!(m)->mnt_ns)
-#define CLEAR_MNT_SHARED(m) ((m)->mnt.mnt_flags &= ~MNT_SHARED)
-#define IS_MNT_UNBINDABLE(m) ((m)->mnt.mnt_flags & MNT_UNBINDABLE)
-#define IS_MNT_MARKED(m) ((m)->mnt.mnt_flags & MNT_MARKED)
-#define SET_MNT_MARK(m) ((m)->mnt.mnt_flags |= MNT_MARKED)
-#define CLEAR_MNT_MARK(m) ((m)->mnt.mnt_flags &= ~MNT_MARKED)
+#define CLEAR_MNT_SHARED(m) ((m)->mnt_t_flags &= ~T_SHARED)
+#define IS_MNT_UNBINDABLE(m) ((m)->mnt_t_flags & T_UNBINDABLE)
+#define IS_MNT_MARKED(m) ((m)->mnt_t_flags & T_MARKED)
+#define SET_MNT_MARK(m) ((m)->mnt_t_flags |= T_MARKED)
+#define CLEAR_MNT_MARK(m) ((m)->mnt_t_flags &= ~T_MARKED)
 #define IS_MNT_LOCKED(m) ((m)->mnt.mnt_flags & MNT_LOCKED)
 
 #define CL_EXPIRE    		0x01
@@ -25,19 +25,26 @@
 #define CL_COPY_UNBINDABLE	0x04
 #define CL_MAKE_SHARED 		0x08
 #define CL_PRIVATE 		0x10
-#define CL_SHARED_TO_SLAVE	0x20
 #define CL_COPY_MNT_NS_FILE	0x40
 
+/*
+ * EXCL[namespace_sem]
+ */
 static inline void set_mnt_shared(struct mount *mnt)
 {
-	mnt->mnt.mnt_flags &= ~MNT_SHARED_MASK;
-	mnt->mnt.mnt_flags |= MNT_SHARED;
+	mnt->mnt_t_flags &= ~T_SHARED_MASK;
+	mnt->mnt_t_flags |= T_SHARED;
+}
+
+static inline bool peers(const struct mount *m1, const struct mount *m2)
+{
+	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
 }
 
 void change_mnt_propagation(struct mount *, int);
 int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
 		struct hlist_head *);
-int propagate_umount(struct list_head *);
+void propagate_umount(struct list_head *);
 int propagate_mount_busy(struct mount *, int);
 void propagate_mount_unlock(struct mount *);
 void mnt_release_group_id(struct mount *);

include/linux/mount.h

@@ -35,9 +35,6 @@ enum mount_flags {
 	MNT_SHRINKABLE	= 0x100,
 	MNT_WRITE_HOLD	= 0x200,
 
-	MNT_SHARED	= 0x1000, /* if the vfsmount is a shared mount */
-	MNT_UNBINDABLE	= 0x2000, /* if the vfsmount is a unbindable mount */
-
 	MNT_INTERNAL	= 0x4000,
 
 	MNT_LOCK_ATIME		= 0x040000,
@@ -48,25 +45,15 @@ enum mount_flags {
 	MNT_LOCKED		= 0x800000,
 	MNT_DOOMED		= 0x1000000,
 	MNT_SYNC_UMOUNT		= 0x2000000,
-	MNT_MARKED		= 0x4000000,
 	MNT_UMOUNT		= 0x8000000,
 
-	/*
-	 * MNT_SHARED_MASK is the set of flags that should be cleared when a
-	 * mount becomes shared.  Currently, this is only the flag that says a
-	 * mount cannot be bind mounted, since this is how we create a mount
-	 * that shares events with another mount.  If you add a new MNT_*
-	 * flag, consider how it interacts with shared mounts.
-	 */
-	MNT_SHARED_MASK	= MNT_UNBINDABLE,
 	MNT_USER_SETTABLE_MASK  = MNT_NOSUID | MNT_NODEV | MNT_NOEXEC
 				  | MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME
 				  | MNT_READONLY | MNT_NOSYMFOLLOW,
 	MNT_ATIME_MASK = MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME,
 
-	MNT_INTERNAL_FLAGS = MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL |
-			     MNT_DOOMED | MNT_SYNC_UMOUNT | MNT_MARKED |
-			     MNT_LOCKED,
+	MNT_INTERNAL_FLAGS = MNT_WRITE_HOLD | MNT_INTERNAL | MNT_DOOMED |
+			     MNT_SYNC_UMOUNT | MNT_LOCKED
 };
 
 struct vfsmount {
@@ -98,6 +85,7 @@ int mnt_get_write_access(struct vfsmount *mnt);
 void mnt_put_write_access(struct vfsmount *mnt);
 
 extern struct vfsmount *fc_mount(struct fs_context *fc);
+extern struct vfsmount *fc_mount_longterm(struct fs_context *fc);
 extern struct vfsmount *vfs_create_mount(struct fs_context *fc);
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 				      int flags, const char *name,

ipc/mqueue.c

@@ -483,7 +483,7 @@ static struct vfsmount *mq_create_mount(struct ipc_namespace *ns)
 	put_user_ns(fc->user_ns);
 	fc->user_ns = get_user_ns(ctx->ipc_ns->user_ns);
 
-	mnt = fc_mount(fc);
+	mnt = fc_mount_longterm(fc);
 	put_fs_context(fc);
 	return mnt;
 }