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kernfs: remove iattr_mutex

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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/20250623063854.1896364-2-song@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-06-22 23:38:51 -07:00
parent 19272b37aa
commit d1f4e90260
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 38 additions and 32 deletions
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70
fs/kernfs/inode.c
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@ -24,45 +24,46 @@ static const struct inode_operations kernfs_iops = {
.listxattr = kernfs_iop_listxattr, .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 __free(kfree) = NULL;
struct kernfs_iattrs *ret; struct kernfs_iattrs *attr;
mutex_lock(&iattr_mutex); attr = READ_ONCE(kn->iattr);
if (attr || !alloc)
return attr;
if (kn->iattr || !alloc) ret = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
goto out_unlock; if (!ret)
return NULL;
kn->iattr = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
if (!kn->iattr)
goto out_unlock;
/* assign default attributes */ /* assign default attributes */
kn->iattr->ia_uid = GLOBAL_ROOT_UID; ret->ia_uid = GLOBAL_ROOT_UID;
kn->iattr->ia_gid = GLOBAL_ROOT_GID; ret->ia_gid = GLOBAL_ROOT_GID;
ktime_get_real_ts64(&kn->iattr->ia_atime); ktime_get_real_ts64(&ret->ia_atime);
kn->iattr->ia_mtime = kn->iattr->ia_atime; ret->ia_mtime = ret->ia_atime;
kn->iattr->ia_ctime = kn->iattr->ia_atime; ret->ia_ctime = ret->ia_atime;
simple_xattrs_init(&kn->iattr->xattrs); simple_xattrs_init(&ret->xattrs);
atomic_set(&kn->iattr->nr_user_xattrs, 0); atomic_set(&ret->nr_user_xattrs, 0);
atomic_set(&kn->iattr->user_xattr_size, 0); atomic_set(&ret->user_xattr_size, 0);
out_unlock:
ret = kn->iattr; /* If someone raced us, recognize it. */
mutex_unlock(&iattr_mutex); if (!try_cmpxchg(&kn->iattr, &attr, ret))
return ret; return READ_ONCE(kn->iattr);
return no_free_ptr(ret);
} }
static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn) 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) 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) 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_node *kn = kernfs_dentry_node(dentry);
struct kernfs_iattrs *attrs; struct kernfs_iattrs *attrs;
attrs = kernfs_iattrs(kn); attrs = kernfs_iattrs_noalloc(kn);
if (!attrs) if (!attrs)
return -ENOMEM; return -ENODATA;
return simple_xattr_list(d_inode(dentry), &attrs->xattrs, buf, size); 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) 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; inode->i_mode = kn->mode;
attrs = kernfs_iattrs_noalloc(kn);
if (attrs) if (attrs)
/* /*
* kernfs_node has non-default attributes get them from * 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) const void *value, size_t size, int flags)
{ {
struct simple_xattr *old_xattr; struct simple_xattr *old_xattr;
struct kernfs_iattrs *attrs = kernfs_iattrs(kn); struct kernfs_iattrs *attrs;
attrs = kernfs_iattrs(kn);
if (!attrs) if (!attrs)
return -ENOMEM; return -ENOMEM;
@ -345,8 +349,9 @@ static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn,
struct simple_xattrs *xattrs, struct simple_xattrs *xattrs,
const void *value, size_t size, int flags) const void *value, size_t size, int flags)
{ {
atomic_t *sz = &kn->iattr->user_xattr_size; struct kernfs_iattrs *attr = kernfs_iattrs_noalloc(kn);
atomic_t *nr = &kn->iattr->nr_user_xattrs; atomic_t *sz = &attr->user_xattr_size;
atomic_t *nr = &attr->nr_user_xattrs;
struct simple_xattr *old_xattr; struct simple_xattr *old_xattr;
int ret; int ret;
@ -384,8 +389,9 @@ static int kernfs_vfs_user_xattr_rm(struct kernfs_node *kn,
struct simple_xattrs *xattrs, struct simple_xattrs *xattrs,
const void *value, size_t size, int flags) const void *value, size_t size, int flags)
{ {
atomic_t *sz = &kn->iattr->user_xattr_size; struct kernfs_iattrs *attr = kernfs_iattrs_noalloc(kn);
atomic_t *nr = &kn->iattr->nr_user_xattrs; atomic_t *sz = &attr->user_xattr_size;
atomic_t *nr = &attr->nr_user_xattrs;
struct simple_xattr *old_xattr; struct simple_xattr *old_xattr;
old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags); old_xattr = simple_xattr_set(xattrs, full_name, value, size, flags);