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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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24
mm/shmem.c
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@@ -4038,6 +4038,7 @@ 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))
@@ -4050,16 +4051,23 @@ static int shmem_rename2(struct mnt_idmap *idmap,
if (!simple_empty(new_dentry))
return -ENOTEMPTY;
if (flags & RENAME_WHITEOUT) {
error = shmem_whiteout(idmap, old_dir, old_dentry);
if (error)
return error;
}
error = simple_offset_rename(old_dir, old_dentry, new_dir, new_dentry);
if (error)
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 (!had_offset)
simple_offset_remove(shmem_get_offset_ctx(new_dir),
new_dentry);
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) {