[RFC PATCH v6.6 04/10] libfs: Fix simple_offset_rename_exchange()

cel
2025-01-24T19:20:05Z

[ Upstream commit 23cdd0eed3f1fff3af323092b0b88945a7950d8e ]

User space expects the replacement (old) directory entry to have
the same directory offset after the rename.

Suggested-by: Christian Brauner <brauner@kernel.org>
Fixes: a2e459555c5f ("shmem: stable directory offsets")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/20240415152057.4605-2-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
[ cel: adjusted to apply to origin/linux-6.6.y ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
fs/libfs.c | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index d7b901cb9af4..2029cb6a0e15 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -294,6 +294,18 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
return 0;
}

+static int simple_offset_replace(struct offset_ctx *octx, struct dentry *dentry,
+ long offset)
+{
+ void *ret;
+
+ ret = xa_store(&octx->xa, offset, dentry, GFP_KERNEL);
+ if (xa_is_err(ret))
+ return xa_err(ret);
+ offset_set(dentry, offset);
+ return 0;
+}
+
/**
* simple_offset_remove - Remove an entry to a directory's offset map
* @octx: directory offset ctx to be updated
@@ -351,6 +363,9 @@ int simple_offset_empty(struct dentry *dentry)
* @new_dir: destination parent
* @new_dentry: destination dentry
*
+ * This API preserves the directory offset values. Caller provides
+ * appropriate serialization.
+ *
* Returns zero on success. Otherwise a negative errno is returned and the
* rename is rolled back.
*/
@@ -368,11 +383,11 @@ int simple_offset_rename_exchange(struct inode *old_dir,
simple_offset_remove(old_ctx, old_dentry);
simple_offset_remove(new_ctx, new_dentry);

- ret = simple_offset_add(new_ctx, old_dentry);
+ ret = simple_offset_replace(new_ctx, old_dentry, new_index);
if (ret)
goto out_restore;

- ret = simple_offset_add(old_ctx, new_dentry);
+ ret = simple_offset_replace(old_ctx, new_dentry, old_index);
if (ret) {
simple_offset_remove(new_ctx, old_dentry);
goto out_restore;
@@ -387,10 +402,8 @@ int simple_offset_rename_exchange(struct inode *old_dir,
return 0;

out_restore:
- offset_set(old_dentry, old_index);
- xa_store(&old_ctx->xa, old_index, old_dentry, GFP_KERNEL);
- offset_set(new_dentry, new_index);
- xa_store(&new_ctx->xa, new_index, new_dentry, GFP_KERNEL);
+ (void)simple_offset_replace(old_ctx, old_dentry, old_index);
+ (void)simple_offset_replace(new_ctx, new_dentry, new_index);
return ret;
}

--
2.47.0