Unverified Commit d1f4e902 authored by Christian Brauner's avatar Christian Brauner
Browse files

kernfs: remove iattr_mutex 



All allocations of struct kernfs_iattrs are serialized through a global
mutex. Simply do a racy allocation and let the first one win. I bet most
callers are under inode->i_rwsem anyway and it wouldn't be needed but
let's not require that.

Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/20250623063854.1896364-2-song@kernel.org


Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 19272b37

fs/kernfs/inode.c

+40 −34
Original line number Diff line number Diff line
@@ -24,45 +24,46 @@ static const struct inode_operations kernfs_iops = { 
	.listxattr	= kernfs_iop_listxattr,

};



static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, int alloc)

static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, bool alloc)

{

	static DEFINE_MUTEX(iattr_mutex);

	struct kernfs_iattrs *ret;

	struct kernfs_iattrs *ret __free(kfree) = NULL;

	struct kernfs_iattrs *attr;



	mutex_lock(&iattr_mutex);

	attr = READ_ONCE(kn->iattr);

	if (attr || !alloc)

		return attr;



	if (kn->iattr || !alloc)

		goto out_unlock;



	kn->iattr = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);

	if (!kn->iattr)

		goto out_unlock;

	ret = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);

	if (!ret)

		return NULL;



	/* assign default attributes */

	kn->iattr->ia_uid = GLOBAL_ROOT_UID;

	kn->iattr->ia_gid = GLOBAL_ROOT_GID;



	ktime_get_real_ts64(&kn->iattr->ia_atime);

	kn->iattr->ia_mtime = kn->iattr->ia_atime;

	kn->iattr->ia_ctime = kn->iattr->ia_atime;



	simple_xattrs_init(&kn->iattr->xattrs);

	atomic_set(&kn->iattr->nr_user_xattrs, 0);

	atomic_set(&kn->iattr->user_xattr_size, 0);

out_unlock:

	ret = kn->iattr;

	mutex_unlock(&iattr_mutex);

	return ret;

	ret->ia_uid = GLOBAL_ROOT_UID;

	ret->ia_gid = GLOBAL_ROOT_GID;



	ktime_get_real_ts64(&ret->ia_atime);

	ret->ia_mtime = ret->ia_atime;

	ret->ia_ctime = ret->ia_atime;



	simple_xattrs_init(&ret->xattrs);

	atomic_set(&ret->nr_user_xattrs, 0);

	atomic_set(&ret->user_xattr_size, 0);



	/* If someone raced us, recognize it. */

	if (!try_cmpxchg(&kn->iattr, &attr, ret))

		return READ_ONCE(kn->iattr);



	return no_free_ptr(ret);

}



static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)

{

	return __kernfs_iattrs(kn, 1);

	return __kernfs_iattrs(kn, true);

}



static struct kernfs_iattrs *kernfs_iattrs_noalloc(struct kernfs_node *kn)

{

	return __kernfs_iattrs(kn, 0);

	return __kernfs_iattrs(kn, false);

}



int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
@@ -141,9 +142,9 @@ ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size) 
	struct kernfs_node *kn = kernfs_dentry_node(dentry);

	struct kernfs_iattrs *attrs;



	attrs = kernfs_iattrs(kn);

	attrs = kernfs_iattrs_noalloc(kn);

	if (!attrs)

		return -ENOMEM;

		return -ENODATA;



	return simple_xattr_list(d_inode(dentry), &attrs->xattrs, buf, size);

}
@@ -166,9 +167,10 @@ static inline void set_inode_attr(struct inode *inode, 


static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode)

{

	struct kernfs_iattrs *attrs = kn->iattr;

	struct kernfs_iattrs *attrs;



	inode->i_mode = kn->mode;

	attrs = kernfs_iattrs_noalloc(kn);

	if (attrs)

		/*

		 * kernfs_node has non-default attributes get them from
@@ -306,7 +308,9 @@ int kernfs_xattr_set(struct kernfs_node *kn, const char *name, 
		     const void *value, size_t size, int flags)

{

	struct simple_xattr *old_xattr;

	struct kernfs_iattrs *attrs = kernfs_iattrs(kn);

	struct kernfs_iattrs *attrs;



	attrs = kernfs_iattrs(kn);

	if (!attrs)

		return -ENOMEM;
@@ -345,8 +349,9 @@ static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn, 
				     struct simple_xattrs *xattrs,

				     const void *value, size_t size, int flags)

{

	atomic_t *sz = &kn->iattr->user_xattr_size;

	atomic_t *nr = &kn->iattr->nr_user_xattrs;

	struct kernfs_iattrs *attr = kernfs_iattrs_noalloc(kn);

	atomic_t *sz = &attr->user_xattr_size;

	atomic_t *nr = &attr->nr_user_xattrs;

	struct simple_xattr *old_xattr;

	int ret;
@@ -384,8 +389,9 @@ static int kernfs_vfs_user_xattr_rm(struct kernfs_node *kn, 
				    struct simple_xattrs *xattrs,

				    const void *value, size_t size, int flags)

{

	atomic_t *sz = &kn->iattr->user_xattr_size;

	atomic_t *nr = &kn->iattr->nr_user_xattrs;

	struct kernfs_iattrs *attr = kernfs_iattrs_noalloc(kn);

	atomic_t *sz = &attr->user_xattr_size;

	atomic_t *nr = &attr->nr_user_xattrs;

	struct simple_xattr *old_xattr;



	old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags);