Commit e1b4c6a5 authored by Al Viro's avatar Al Viro
Browse files

shmem: fix recovery on rename failures 



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: a2e45955 ("shmem: stable directory offsets")
Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Reviewed-by: default avatarChuck Lever <chuck.lever@oracle.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 3010f06c

fs/libfs.c

+21 −29
Original line number Diff line number Diff line
@@ -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,

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) {

	simple_offset_remove(old_ctx, old_dentry);

	offset_set(new_dentry, 0);

		return simple_offset_replace(new_ctx, old_dentry, new_offset);

	}

	return simple_offset_add(new_ctx, old_dentry);

	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;

}



/**

include/linux/fs.h

+1 −1
Original line number Diff line number Diff line
@@ -3247,7 +3247,7 @@ 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,

mm/shmem.c

+13 −5
Original line number Diff line number Diff line
@@ -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;



	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) {