libfs: Add simple_offset_empty()

For simple filesystems that use directory offset mapping, rely
strictly on the directory offset map to tell when a directory has
no children.

After this patch is applied, the emptiness test holds only the RCU
read lock when the directory being tested has no children.

In addition, this adds another layer of confirmation that
simple_offset_add/remove() are working as expected.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/170820143463.6328.7872919188371286951.stgit@91.116.238.104.host.secureserver.net
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/libfs.c b/fs/libfs.c
index f0045db739df892efae90730517279620a6cfc01..f7f92a49a41827fa946e3f3ee8b27efa782eda69 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -313,6 +313,38 @@ void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
        offset_set(dentry, 0);
 }
 
+/**
+ * simple_offset_empty - Check if a dentry can be unlinked
+ * @dentry: dentry to be tested
+ *
+ * Returns 0 if @dentry is a non-empty directory; otherwise returns 1.
+ */
+int simple_offset_empty(struct dentry *dentry)
+{
+       struct inode *inode = d_inode(dentry);
+       struct offset_ctx *octx;
+       struct dentry *child;
+       unsigned long index;
+       int ret = 1;
+
+       if (!inode || !S_ISDIR(inode->i_mode))
+               return ret;
+
+       index = DIR_OFFSET_MIN;
+       octx = inode->i_op->get_offset_ctx(inode);
+       xa_for_each(&octx->xa, index, child) {
+               spin_lock(&child->d_lock);
+               if (simple_positive(child)) {
+                       spin_unlock(&child->d_lock);
+                       ret = 0;
+                       break;
+               }
+               spin_unlock(&child->d_lock);
+       }
+
+       return ret;
+}
+
 /**
  * simple_offset_rename_exchange - exchange rename with directory offsets
  * @old_dir: parent of dentry being moved

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ed5966a70495129be1d6729eed2918240db62df1..03d141809a2c64b03b240fbab92c6b90fa247fca 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3267,6 +3267,7 @@ struct offset_ctx {
 void simple_offset_init(struct offset_ctx *octx);
 int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry);
 void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry);
+int simple_offset_empty(struct dentry *dentry);
 int simple_offset_rename_exchange(struct inode *old_dir,
                                  struct dentry *old_dentry,
                                  struct inode *new_dir,

diff --git a/mm/shmem.c b/mm/shmem.c
index d7c84ff621860b85090cf61d9b2970357da01b76..6fed524343cb2ad6c628567d5563c619c31c4ad4 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3374,7 +3374,7 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
 
 static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
 {
-       if (!simple_empty(dentry))
+       if (!simple_offset_empty(dentry))
                return -ENOTEMPTY;
 
        drop_nlink(d_inode(dentry));
@@ -3431,7 +3431,7 @@ static int shmem_rename2(struct mnt_idmap *idmap,
                return simple_offset_rename_exchange(old_dir, old_dentry,
                                                     new_dir, new_dentry);
 
-       if (!simple_empty(new_dentry))
+       if (!simple_offset_empty(new_dentry))
                return -ENOTEMPTY;
 
        if (flags & RENAME_WHITEOUT) {