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shmem: fix recovery on rename failures

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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: a2e459555c ("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>
This commit is contained in:
Al Viro
2025-12-13 17:50:23 -05:00
parent 3010f06c52
commit e1b4c6a583
3 changed files with 38 additions and 38 deletions
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50
fs/libfs.c
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@@ -346,22 +346,22 @@ 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));
}
/**
@@ -388,31 +388,23 @@ 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;
}
/**