[PATCH 6.12 005/567] shmem: fix recovery on rename failures

Greg Kroah-Hartman
2026-01-06T17:16:06Z

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit e1b4c6a58304fd490124cc2b454d80edc786665c ]

maple_tree insertions can fail if we are seriously short on memory;
simple_offset_rename() does not recover well if it runs into that.
The same goes for simple_offset_rename_exchange().

Moreover, shmem_whiteout() expects that if it succeeds, the caller will
progress to d_move(), i.e. that shmem_rename2() won't fail past the
successful call of shmem_whiteout().

Not hard to fix, fortunately - mtree_store() can't fail if the index we
are trying to store into is already present in the tree as a singleton.

For simple_offset_rename_exchange() that's enough - we just need to be
careful about the order of operations.

For simple_offset_rename() solution is to preinsert the target into the
tree for new_dir; the rest can be done without any potentially failing
operations.

That preinsertion has to be done in shmem_rename2() rather than in
simple_offset_rename() itself - otherwise we'd need to deal with the
possibility of failure after successful shmem_whiteout().

Fixes: a2e459555c5f ("shmem: stable directory offsets")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/libfs.c | 50 +++++++++++++++++++---------------------------
include/linux/fs.h | 2 +-
mm/shmem.c | 18 ++++++++++++-----
3 files changed, 35 insertions(+), 35 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 8743241678496..028f2cf729d5d 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -345,22 +345,22 @@ void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
* User space expects the directory offset value of the replaced
* (new) directory entry to be unchanged after a rename.
*
- * Returns zero on success, a negative errno value on failure.
+ * Caller must have grabbed a slot for new_dentry in the maple_tree
+ * associated with new_dir, even if dentry is negative.
*/
-int simple_offset_rename(struct inode *old_dir, struct dentry *old_dentry,
- struct inode *new_dir, struct dentry *new_dentry)
+void simple_offset_rename(struct inode *old_dir, struct dentry *old_dentry,
+ struct inode *new_dir, struct dentry *new_dentry)
{
struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir);
struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir);
long new_offset = dentry2offset(new_dentry);

- simple_offset_remove(old_ctx, old_dentry);
+ if (WARN_ON(!new_offset))
+ return;

- if (new_offset) {
- offset_set(new_dentry, 0);
- return simple_offset_replace(new_ctx, old_dentry, new_offset);
- }
- return simple_offset_add(new_ctx, old_dentry);
+ simple_offset_remove(old_ctx, old_dentry);
+ offset_set(new_dentry, 0);
+ WARN_ON(simple_offset_replace(new_ctx, old_dentry, new_offset));
}

/**
@@ -387,31 +387,23 @@ int simple_offset_rename_exchange(struct inode *old_dir,
long new_index = dentry2offset(new_dentry);
int ret;

- simple_offset_remove(old_ctx, old_dentry);
- simple_offset_remove(new_ctx, new_dentry);
+ if (WARN_ON(!old_index || !new_index))
+ return -EINVAL;

- ret = simple_offset_replace(new_ctx, old_dentry, new_index);
- if (ret)
- goto out_restore;
+ ret = mtree_store(&new_ctx->mt, new_index, old_dentry, GFP_KERNEL);
+ if (WARN_ON(ret))
+ return ret;

- ret = simple_offset_replace(old_ctx, new_dentry, old_index);
- if (ret) {
- simple_offset_remove(new_ctx, old_dentry);
- goto out_restore;
+ ret = mtree_store(&old_ctx->mt, old_index, new_dentry, GFP_KERNEL);
+ if (WARN_ON(ret)) {
+ mtree_store(&new_ctx->mt, new_index, new_dentry, GFP_KERNEL);
+ return ret;
}

- ret = simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
- if (ret) {
- simple_offset_remove(new_ctx, old_dentry);
- simple_offset_remove(old_ctx, new_dentry);
- goto out_restore;
- }
+ offset_set(old_dentry, new_index);
+ offset_set(new_dentry, old_index);
+ simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
return 0;
-
-out_restore:
- (void)simple_offset_replace(old_ctx, old_dentry, old_index);
- (void)simple_offset_replace(new_ctx, new_dentry, new_index);
- return ret;
}

/**
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 37a01c9d96583..87720e1b54192 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3446,7 +3446,7 @@ 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_rename(struct inode *old_dir, struct dentry *old_dentry,
+void simple_offset_rename(struct inode *old_dir, struct dentry *old_dentry,
struct inode *new_dir, struct dentry *new_dentry);
int simple_offset_rename_exchange(struct inode *old_dir,
struct dentry *old_dentry,
diff --git a/mm/shmem.c b/mm/shmem.c
index 7e07188e82696..0c3113b5b5aaa 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3749,6 +3749,7 @@ static int shmem_rename2(struct mnt_idmap *idmap,
{
struct inode *inode = d_inode(old_dentry);
int they_are_dirs = S_ISDIR(inode->i_mode);
+ bool had_offset = false;
int error;

if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
@@ -3761,16 +3762,23 @@ static int shmem_rename2(struct mnt_idmap *idmap,
if (!simple_empty(new_dentry))
return -ENOTEMPTY;

+ error = simple_offset_add(shmem_get_offset_ctx(new_dir), new_dentry);
+ if (error == -EBUSY)
+ had_offset = true;
+ else if (unlikely(error))
+ return error;
+
if (flags & RENAME_WHITEOUT) {
error = shmem_whiteout(idmap, old_dir, old_dentry);
- if (error)
+ if (error) {
+ if (!had_offset)
+ simple_offset_remove(shmem_get_offset_ctx(new_dir),
+ new_dentry);
return error;
+ }
}

- error = simple_offset_rename(old_dir, old_dentry, new_dir, new_dentry);
- if (error)
- return error;
-
+ simple_offset_rename(old_dir, old_dentry, new_dir, new_dentry);
if (d_really_is_positive(new_dentry)) {
(void) shmem_unlink(new_dir, new_dentry);
if (they_are_dirs) {
--
2.51.0