[PATCH 03/14] shmem: adapt to rhashtable-based simple_xattrs with lazy allocation
From: Christian Brauner
Date: Mon Feb 16 2026 - 08:33:26 EST
Adapt tmpfs/shmem to use the rhashtable-based xattr path and switch
from an embedded struct to pointer-based lazy allocation.
Change shmem_inode_info.xattrs from embedded 'struct simple_xattrs' to
a pointer 'struct simple_xattrs *', initialized to NULL. This avoids
the rhashtable overhead for every tmpfs inode, which helps when a lot of
inodes exist.
The xattr store is allocated on first use:
- shmem_initxattrs(): Allocates via simple_xattrs_alloc() when
security modules set initial xattrs during inode creation.
- shmem_xattr_handler_set(): Allocates on first setxattr, with a
short-circuit for removal when no xattrs are stored yet.
All read paths (shmem_xattr_handler_get, shmem_listxattr) check for
NULL xattrs pointer and return -ENODATA or 0 respectively.
Replaced xattr entries are freed via simple_xattr_free_rcu() to allow
concurrent RCU readers to finish.
shmem_evict_inode() conditionally frees the xattr store only when
allocated.
Also change simple_xattr_add() from void to int to propagate
rhashtable insertion failures. shmem_initxattrs() is the only caller.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
fs/xattr.c | 26 +++++++++++++-------------
include/linux/shmem_fs.h | 2 +-
include/linux/xattr.h | 4 ++--
mm/shmem.c | 44 +++++++++++++++++++++++++++++++-------------
4 files changed, 47 insertions(+), 29 deletions(-)
diff --git a/fs/xattr.c b/fs/xattr.c
index 1d98ea459b7b..eb45ae0fd17f 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -1677,19 +1677,19 @@ static bool rbtree_simple_xattr_less(struct rb_node *new_node,
* of matching xattrs is wanted. Should only be called during inode
* initialization when a few distinct initial xattrs are supposed to be set.
*/
-void simple_xattr_add(struct simple_xattrs *xattrs,
- struct simple_xattr *new_xattr)
-{
- if (xattrs->use_rhashtable) {
- WARN_ON(rhashtable_insert_fast(&xattrs->ht,
- &new_xattr->hash_node,
- simple_xattr_params));
- } else {
- write_lock(&xattrs->lock);
- rb_add(&new_xattr->rb_node, &xattrs->rb_root,
- rbtree_simple_xattr_less);
- write_unlock(&xattrs->lock);
- }
+int simple_xattr_add(struct simple_xattrs *xattrs,
+ struct simple_xattr *new_xattr)
+{
+ if (xattrs->use_rhashtable)
+ return rhashtable_insert_fast(&xattrs->ht,
+ &new_xattr->hash_node,
+ simple_xattr_params);
+
+ write_lock(&xattrs->lock);
+ rb_add(&new_xattr->rb_node, &xattrs->rb_root,
+ rbtree_simple_xattr_less);
+ write_unlock(&xattrs->lock);
+ return 0;
}
/**
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index e2069b3179c4..53d325409a8b 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -48,7 +48,7 @@ struct shmem_inode_info {
};
struct timespec64 i_crtime; /* file creation time */
struct shared_policy policy; /* NUMA memory alloc policy */
- struct simple_xattrs xattrs; /* list of xattrs */
+ struct simple_xattrs *xattrs; /* list of xattrs */
pgoff_t fallocend; /* highest fallocate endindex */
unsigned int fsflags; /* for FS_IOC_[SG]ETFLAGS */
atomic_t stop_eviction; /* hold when working on inode */
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index ee4fd40717a0..3063ecf0004d 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -142,8 +142,8 @@ struct simple_xattr *simple_xattr_set(struct simple_xattrs *xattrs,
size_t size, int flags);
ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
char *buffer, size_t size);
-void simple_xattr_add(struct simple_xattrs *xattrs,
- struct simple_xattr *new_xattr);
+int simple_xattr_add(struct simple_xattrs *xattrs,
+ struct simple_xattr *new_xattr);
int xattr_list_one(char **buffer, ssize_t *remaining_size, const char *name);
DEFINE_CLASS(simple_xattr,
diff --git a/mm/shmem.c b/mm/shmem.c
index fc8020ce2e9f..8761c9b4f1c5 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1426,7 +1426,10 @@ static void shmem_evict_inode(struct inode *inode)
}
}
- simple_xattrs_free(&info->xattrs, sbinfo->max_inodes ? &freed : NULL);
+ if (info->xattrs) {
+ simple_xattrs_free(info->xattrs, sbinfo->max_inodes ? &freed : NULL);
+ kfree(info->xattrs);
+ }
shmem_free_inode(inode->i_sb, freed);
WARN_ON(inode->i_blocks);
clear_inode(inode);
@@ -3118,7 +3121,6 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
shmem_set_inode_flags(inode, info->fsflags, NULL);
INIT_LIST_HEAD(&info->shrinklist);
INIT_LIST_HEAD(&info->swaplist);
- simple_xattrs_init(&info->xattrs);
cache_no_acl(inode);
if (sbinfo->noswap)
mapping_set_unevictable(inode->i_mapping);
@@ -4270,10 +4272,13 @@ static int shmem_initxattrs(struct inode *inode,
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
const struct xattr *xattr;
- struct simple_xattr *new_xattr;
size_t ispace = 0;
size_t len;
+ CLASS(simple_xattrs, xattrs)();
+ if (IS_ERR(xattrs))
+ return PTR_ERR(xattrs);
+
if (sbinfo->max_inodes) {
for (xattr = xattr_array; xattr->name != NULL; xattr++) {
ispace += simple_xattr_space(xattr->name,
@@ -4292,24 +4297,24 @@ static int shmem_initxattrs(struct inode *inode,
}
for (xattr = xattr_array; xattr->name != NULL; xattr++) {
- new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
+ CLASS(simple_xattr, new_xattr)(xattr->value, xattr->value_len);
if (IS_ERR(new_xattr))
break;
len = strlen(xattr->name) + 1;
new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
GFP_KERNEL_ACCOUNT);
- if (!new_xattr->name) {
- kvfree(new_xattr);
+ if (!new_xattr->name)
break;
- }
memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
XATTR_SECURITY_PREFIX_LEN);
memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
xattr->name, len);
- simple_xattr_add(&info->xattrs, new_xattr);
+ if (simple_xattr_add(xattrs, new_xattr))
+ break;
+ retain_and_null_ptr(new_xattr);
}
if (xattr->name != NULL) {
@@ -4318,10 +4323,10 @@ static int shmem_initxattrs(struct inode *inode,
sbinfo->free_ispace += ispace;
raw_spin_unlock(&sbinfo->stat_lock);
}
- simple_xattrs_free(&info->xattrs, NULL);
return -ENOMEM;
}
+ smp_store_release(&info->xattrs, no_free_ptr(xattrs));
return 0;
}
@@ -4330,9 +4335,14 @@ static int shmem_xattr_handler_get(const struct xattr_handler *handler,
const char *name, void *buffer, size_t size)
{
struct shmem_inode_info *info = SHMEM_I(inode);
+ struct simple_xattrs *xattrs;
+
+ xattrs = READ_ONCE(info->xattrs);
+ if (!xattrs)
+ return -ENODATA;
name = xattr_full_name(handler, name);
- return simple_xattr_get(&info->xattrs, name, buffer, size);
+ return simple_xattr_get(xattrs, name, buffer, size);
}
static int shmem_xattr_handler_set(const struct xattr_handler *handler,
@@ -4343,10 +4353,16 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
{
struct shmem_inode_info *info = SHMEM_I(inode);
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+ struct simple_xattrs *xattrs;
struct simple_xattr *old_xattr;
size_t ispace = 0;
name = xattr_full_name(handler, name);
+
+ xattrs = simple_xattrs_lazy_alloc(&info->xattrs, value, flags);
+ if (IS_ERR_OR_NULL(xattrs))
+ return PTR_ERR(xattrs);
+
if (value && sbinfo->max_inodes) {
ispace = simple_xattr_space(name, size);
raw_spin_lock(&sbinfo->stat_lock);
@@ -4359,13 +4375,13 @@ static int shmem_xattr_handler_set(const struct xattr_handler *handler,
return -ENOSPC;
}
- old_xattr = simple_xattr_set(&info->xattrs, name, value, size, flags);
+ old_xattr = simple_xattr_set(xattrs, name, value, size, flags);
if (!IS_ERR(old_xattr)) {
ispace = 0;
if (old_xattr && sbinfo->max_inodes)
ispace = simple_xattr_space(old_xattr->name,
old_xattr->size);
- simple_xattr_free(old_xattr);
+ simple_xattr_free_rcu(old_xattr);
old_xattr = NULL;
inode_set_ctime_current(inode);
inode_inc_iversion(inode);
@@ -4406,7 +4422,9 @@ static const struct xattr_handler * const shmem_xattr_handlers[] = {
static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
{
struct shmem_inode_info *info = SHMEM_I(d_inode(dentry));
- return simple_xattr_list(d_inode(dentry), &info->xattrs, buffer, size);
+
+ return simple_xattr_list(d_inode(dentry), READ_ONCE(info->xattrs),
+ buffer, size);
}
#endif /* CONFIG_TMPFS_XATTR */
--
2.47.3