Commit 4edbe133 authored by Al Viro's avatar Al Viro
Browse files

make struct mountpoint bear the dentry reference to mountpoint, not struct mount 



Using dput_to_list() to shift the contributing reference from ->mnt_mountpoint
to ->mnt_mp->m_dentry.  Dentries are dropped (with dput_to_list()) as soon
as struct mountpoint is destroyed; in cases where we are under namespace_sem
we use the global list, shrinking it in namespace_unlock().  In case of
detaching stuck MNT_LOCKed children at final mntput_no_expire() we use a local
list and shrink it ourselves.  ->mnt_ex_mountpoint crap is gone.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 9bdebc2b

fs/mount.h

+0 −1
Original line number Diff line number Diff line
@@ -69,7 +69,6 @@ struct mount { 
	int mnt_expiry_mark;		/* true if marked for expiry */

	struct hlist_head mnt_pins;

	struct fs_pin mnt_umount;

	struct dentry *mnt_ex_mountpoint;

} __randomize_layout;



#define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */

fs/namespace.c

+25 −27
Original line number Diff line number Diff line
@@ -69,6 +69,8 @@ static struct hlist_head *mount_hashtable __read_mostly; 
static struct hlist_head *mountpoint_hashtable __read_mostly;

static struct kmem_cache *mnt_cache __read_mostly;

static DECLARE_RWSEM(namespace_sem);

static HLIST_HEAD(unmounted);	/* protected by namespace_sem */

static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */



/* /sys/fs */

struct kobject *fs_kobj;
@@ -172,7 +174,6 @@ unsigned int mnt_get_count(struct mount *mnt) 
static void drop_mountpoint(struct fs_pin *p)

{

	struct mount *m = container_of(p, struct mount, mnt_umount);

	dput(m->mnt_ex_mountpoint);

	pin_remove(p);

	mntput(&m->mnt);

}
@@ -739,7 +740,7 @@ mountpoint: 


	/* Add the new mountpoint to the hash table */

	read_seqlock_excl(&mount_lock);

	new->m_dentry = dentry;

	new->m_dentry = dget(dentry);

	new->m_count = 1;

	hlist_add_head(&new->m_hash, mp_hash(dentry));

	INIT_HLIST_HEAD(&new->m_list);
@@ -752,7 +753,11 @@ done: 
	return mp;

}



static void put_mountpoint(struct mountpoint *mp)

/*

 * vfsmount lock must be held.  Additionally, the caller is responsible

 * for serializing calls for given disposal list.

 */

static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)

{

	if (!--mp->m_count) {

		struct dentry *dentry = mp->m_dentry;
@@ -760,11 +765,18 @@ static void put_mountpoint(struct mountpoint *mp) 
		spin_lock(&dentry->d_lock);

		dentry->d_flags &= ~DCACHE_MOUNTED;

		spin_unlock(&dentry->d_lock);

		dput_to_list(dentry, list);

		hlist_del(&mp->m_hash);

		kfree(mp);

	}

}



/* called with namespace_lock and vfsmount lock */

static void put_mountpoint(struct mountpoint *mp)

{

	__put_mountpoint(mp, &ex_mountpoints);

}



static inline int check_mnt(struct mount *mnt)

{

	return mnt->mnt_ns == current->nsproxy->mnt_ns;
@@ -813,7 +825,7 @@ static struct mountpoint *unhash_mnt(struct mount *mnt) 
 */

static void detach_mnt(struct mount *mnt, struct path *old_path)

{

	old_path->dentry = mnt->mnt_mountpoint;

	old_path->dentry = dget(mnt->mnt_mountpoint);

	old_path->mnt = &mnt->mnt_parent->mnt;

	put_mountpoint(unhash_mnt(mnt));

}
@@ -823,8 +835,6 @@ static void detach_mnt(struct mount *mnt, struct path *old_path) 
 */

static void umount_mnt(struct mount *mnt)

{

	/* old mountpoint will be dropped when we can do that */

	mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;

	put_mountpoint(unhash_mnt(mnt));

}
@@ -837,7 +847,7 @@ void mnt_set_mountpoint(struct mount *mnt, 
{

	mp->m_count++;

	mnt_add_count(mnt, 1);	/* essentially, that's mntget */

	child_mnt->mnt_mountpoint = dget(mp->m_dentry);

	child_mnt->mnt_mountpoint = mp->m_dentry;

	child_mnt->mnt_parent = mnt;

	child_mnt->mnt_mp = mp;

	hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
@@ -864,7 +874,6 @@ static void attach_mnt(struct mount *mnt, 
void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)

{

	struct mountpoint *old_mp = mnt->mnt_mp;

	struct dentry *old_mountpoint = mnt->mnt_mountpoint;

	struct mount *old_parent = mnt->mnt_parent;



	list_del_init(&mnt->mnt_child);
@@ -874,22 +883,6 @@ void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct m 
	attach_mnt(mnt, parent, mp);



	put_mountpoint(old_mp);



	/*

	 * Safely avoid even the suggestion this code might sleep or

	 * lock the mount hash by taking advantage of the knowledge that

	 * mnt_change_mountpoint will not release the final reference

	 * to a mountpoint.

	 *

	 * During mounting, the mount passed in as the parent mount will

	 * continue to use the old mountpoint and during unmounting, the

	 * old mountpoint will continue to exist until namespace_unlock,

	 * which happens well after mnt_change_mountpoint.

	 */

	spin_lock(&old_mountpoint->d_lock);

	old_mountpoint->d_lockref.count--;

	spin_unlock(&old_mountpoint->d_lock);



	mnt_add_count(old_parent, -1);

}
@@ -1142,6 +1135,8 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput); 


static void mntput_no_expire(struct mount *mnt)

{

	LIST_HEAD(list);



	rcu_read_lock();

	if (likely(READ_ONCE(mnt->mnt_ns))) {

		/*
@@ -1182,10 +1177,11 @@ static void mntput_no_expire(struct mount *mnt) 
	if (unlikely(!list_empty(&mnt->mnt_mounts))) {

		struct mount *p, *tmp;

		list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {

			umount_mnt(p);

			__put_mountpoint(unhash_mnt(p), &list);

		}

	}

	unlock_mount_hash();

	shrink_dentry_list(&list);



	if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {

		struct task_struct *task = current;
@@ -1371,16 +1367,18 @@ int may_umount(struct vfsmount *mnt) 


EXPORT_SYMBOL(may_umount);



static HLIST_HEAD(unmounted);	/* protected by namespace_sem */



static void namespace_unlock(void)

{

	struct hlist_head head;

	LIST_HEAD(list);



	hlist_move_list(&unmounted, &head);

	list_splice_init(&ex_mountpoints, &list);



	up_write(&namespace_sem);



	shrink_dentry_list(&list);



	if (likely(hlist_empty(&head)))

		return;

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