autofs: don't bother with atomics for ino->count

All writers are serialized on inode->i_rwsem.  So are the readers
outside of expire.c.  And the readers in expire.c are in the
code that really doesn't care about narrow races - it's looking
for expiry candidates and its callers have to cope with the
possibility of a good candidate becoming busy right under them.

No point bothering with atomic operations - just use int and
mark the non-serialized readers with READ_ONCE().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/autofs/autofs_i.h

@@ -63,7 +63,7 @@ struct autofs_info {
 
 	struct autofs_sb_info *sbi;
 	unsigned long last_used;
-	atomic_t count;
+	int count;
 
 	kuid_t uid;
 	kgid_t gid;

fs/autofs/expire.c

@@ -211,7 +211,7 @@ static int autofs_tree_busy(struct vfsmount *mnt,
 			}
 		} else {
 			struct autofs_info *ino = autofs_dentry_ino(p);
-			unsigned int ino_count = atomic_read(&ino->count);
+			unsigned int ino_count = READ_ONCE(ino->count);
 
 			/* allow for dget above and top is already dgot */
 			if (p == top)
@@ -379,7 +379,7 @@ static struct dentry *should_expire(struct dentry *dentry,
 		/* Not a forced expire? */
 		if (!(how & AUTOFS_EXP_FORCED)) {
 			/* ref-walk currently on this dentry? */
-			ino_count = atomic_read(&ino->count) + 1;
+			ino_count = READ_ONCE(ino->count) + 1;
 			if (d_count(dentry) > ino_count)
 				return NULL;
 		}
@@ -396,7 +396,7 @@ static struct dentry *should_expire(struct dentry *dentry,
 		/* Not a forced expire? */
 		if (!(how & AUTOFS_EXP_FORCED)) {
 			/* ref-walk currently on this dentry? */
-			ino_count = atomic_read(&ino->count) + 1;
+			ino_count = READ_ONCE(ino->count) + 1;
 			if (d_count(dentry) > ino_count)
 				return NULL;
 		}

fs/autofs/root.c

@@ -569,9 +569,9 @@ static int autofs_dir_symlink(struct inode *dir,
 	d_add(dentry, inode);
 
 	dget(dentry);
-	atomic_inc(&ino->count);
+	ino->count++;
 	p_ino = autofs_dentry_ino(dentry->d_parent);
-	atomic_inc(&p_ino->count);
+	p_ino->count++;
 
 	dir->i_mtime = current_time(dir);
 
@@ -609,9 +609,9 @@ static int autofs_dir_unlink(struct inode *dir, struct dentry *dentry)
 	if (sbi->flags & AUTOFS_SBI_CATATONIC)
 		return -EACCES;
 
-	atomic_dec(&ino->count);
+	ino->count--;
 	p_ino = autofs_dentry_ino(dentry->d_parent);
-	atomic_dec(&p_ino->count);
+	p_ino->count--;
 	dput(ino->dentry);
 
 	d_inode(dentry)->i_size = 0;
@@ -669,7 +669,7 @@ static void autofs_clear_leaf_automount_flags(struct dentry *dentry)
 	/* only consider parents below dentrys in the root */
 	if (IS_ROOT(parent->d_parent))
 		return;
-	if (atomic_read(&autofs_dentry_ino(parent)->count) == 2)
+	if (autofs_dentry_ino(parent)->count == 2)
 		managed_dentry_set_managed(parent);
 }
 
@@ -691,7 +691,7 @@ static int autofs_dir_rmdir(struct inode *dir, struct dentry *dentry)
 	if (sbi->flags & AUTOFS_SBI_CATATONIC)
 		return -EACCES;
 
-	if (atomic_read(&ino->count) != 1)
+	if (ino->count != 1)
 		return -ENOTEMPTY;
 
 	spin_lock(&sbi->lookup_lock);
@@ -702,9 +702,9 @@ static int autofs_dir_rmdir(struct inode *dir, struct dentry *dentry)
 	if (sbi->version < 5)
 		autofs_clear_leaf_automount_flags(dentry);
 
-	atomic_dec(&ino->count);
+	ino->count--;
 	p_ino = autofs_dentry_ino(dentry->d_parent);
-	atomic_dec(&p_ino->count);
+	p_ino->count--;
 	dput(ino->dentry);
 	d_inode(dentry)->i_size = 0;
 	clear_nlink(d_inode(dentry));
@@ -750,9 +750,9 @@ static int autofs_dir_mkdir(struct inode *dir,
 		autofs_set_leaf_automount_flags(dentry);
 
 	dget(dentry);
-	atomic_inc(&ino->count);
+	ino->count++;
 	p_ino = autofs_dentry_ino(dentry->d_parent);
-	atomic_inc(&p_ino->count);
+	p_ino->count++;
 	inc_nlink(dir);
 	dir->i_mtime = current_time(dir);