linux-stable.git/fs/xattr.c, branch linux-rolling-stable

simpe_xattr: use per-sb cache

2026-07-24T14:19:35+00:00

[ Upstream commit 1e7cd8a53b72a58a44c4d282aed95f6ce0e76db0 ]

Move the hash table to the super block to remove excessive overhead in case
of small number of xattrs per inode.

Add linked list to the inode, used for listxattr and eviction.  Listxattr
uses rcu protection to iterate the list of xattrs.

Before being made per-sb, lazy allocation was protected by inode lock.  Now
inode lock no longer provides sufficient exclusion, so use cmpxchg() to
ensure atomicity.

Though I haven't found a description of this pattern, after some research
it seems that cmpxchg_release() and READ_ONCE() should provide the
necessary memory barriers.

Use simple_xattr_free_rcu() in simple_xattrs_free(). This is needed because
the hash table is now shared between inodes and lookup on a different inode
might be running the compare function on the just freed element within the
RCU grace period.

Following stats are based on slabinfo diff, after creating 100k empty
files, then adding a "user.test=foo" xattr to each:

v7.0 (no rhashtable):
  File creation: 993.40 bytes/file
  Xattr addition: 79.99 bytes/file

v7.1-rc2 (per-inode rhashtable):
  File creation: 939.73 bytes/file
  Xattr addition: 1296.08 bytes/file

v7.1-rc2 + this patch (per-sb rhashtable)
  File creation: 946.84 bytes/file
  Xattr addition: 111.86 bytes/file

The overhead of a single xattr is reduced to nearly v7.0 levels.  The per
xattr overhead is slightly larger due to the addition of three pointers to
struct simple_xattr.

Fixes: b32c4a213698 ("xattr: add rhashtable-based simple_xattr infrastructure")
Signed-off-by: Miklos Szeredi 
Link: https://patch.msgid.link/20260605135322.2632068-5-mszeredi@redhat.com
Signed-off-by: Christian Brauner (Amutable) 
Signed-off-by: Sasha Levin

simple_xattr: change interface to pass struct simple_xattrs **

2026-07-24T14:19:35+00:00

[ Upstream commit 076e5cef28e27febfc09b5f72544d2b857c75201 ]

Change the simple_xattr API to accept pointer-to-pointer (struct
simple_xattrs **) instead of pointer.  This allows the functions to handle
lazy allocation internally without requiring callers to use
simple_xattrs_lazy_alloc().

The simple_xattr_set(), simple_xattr_set_limited() and simple_xattr_add()
functions now handle allocation when xattrs is NULL.  simple_xattrs_free()
now also frees the xattrs structure itself and sets the pointer to NULL.

This simplifies callers and removes the need for most callers to explicitly
manage xattrs allocation and lifetime.

In shmem_initxattrs(), the total required space for all initial xattrs
(ispace) is pre-calculated and deducted from sbinfo->free_ispace.

Since this patch modifies the function to add new xattrs directly to the
inode's &info->xattrs list rather than using a local temporary variable, a
failure means that the partially populated info->xattrs list remains
attached to the inode.

When the VFS caller handles the -ENOMEM error, it drops the newly created
inode via iput(), shmem_free_inode() adds freed to sbinfo->free_ispace a
second time, permanently inflating the tmpfs free space quota.

Fix by substracting already added xattrs from ispace.

Signed-off-by: Miklos Szeredi 
Link: https://patch.msgid.link/20260605135322.2632068-4-mszeredi@redhat.com
Signed-off-by: Christian Brauner (Amutable) 
Stable-dep-of: 1e7cd8a53b72 ("simpe_xattr: use per-sb cache")
Signed-off-by: Sasha Levin

xattr: support extended attributes on sockets

2026-03-02T10:06:42+00:00

Allow user.* extended attributes on sockets by adding S_IFSOCK to the
xattr_permission() switch statement. Previously user.* xattrs were only
permitted on regular files and directories. Symlinks and special files
including sockets were rejected with -EPERM.

Path-based AF_UNIX sockets have their inodes on the underlying
filesystem (e.g. tmpfs) which already supports user.* xattrs through
simple_xattrs. So for these the permission check was the only thing
missing.

For sockets in sockfs - everything created via socket() including
abstract namespace AF_UNIX sockets - the preceding patch added
simple_xattr storage with per-inode limits. With the permission check
lifted here these sockets can now store user.* xattrs as well.

This enables services to associate metadata with their sockets. For
example, a service using Varlink for IPC can label its socket with
user.varlink=1 allowing eBPF programs to selectively capture traffic
and tools to discover IPC entrypoints by enumerating bound sockets via
netlink. Similarly, protocol negotiation can be performed through xattrs
such as indicating RFC 5424 structured syslog support on /dev/log.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-11-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Reviewed-by: Jan Kara 
Signed-off-by: Christian Brauner

xattr: move user limits for xattrs to generic infra

2026-03-02T10:06:42+00:00

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-9-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Signed-off-by: Christian Brauner

xattr: switch xattr_permission() to switch statement

2026-03-02T10:06:42+00:00

Simplify the codeflow by using a switch statement that switches on
S_IFMT.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-8-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Reviewed-by: Jan Kara 
Signed-off-by: Christian Brauner

xattr: add xattr_permission_error()

2026-03-02T10:06:42+00:00

Stop repeating the ?: in multiple places and use a simple helper for
this.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-7-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Reviewed-by: Jan Kara 
Signed-off-by: Christian Brauner

xattr: remove rbtree-based simple_xattr infrastructure

2026-03-02T10:06:42+00:00

Now that all consumers (shmem, kernfs, pidfs) have been converted to
use the rhashtable-based simple_xattrs with pointer-based lazy
allocation, remove the legacy rbtree code path. The rhashtable
implementation provides O(1) average-case lookup with RCU-based lockless
reads, replacing the O(log n) rbtree with reader-writer spinlock
contention.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-6-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Signed-off-by: Christian Brauner

shmem: adapt to rhashtable-based simple_xattrs with lazy allocation

2026-02-23T12:06:38+00:00

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.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-3-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Reviewed-by: Jan Kara 
Signed-off-by: Christian Brauner

xattr: add rhashtable-based simple_xattr infrastructure

2026-02-23T12:06:38+00:00

Add rhashtable support to the simple_xattr subsystem while keeping the
existing rbtree code fully functional. This allows consumers to be
migrated one at a time without breaking any intermediate build.

struct simple_xattrs gains a dispatch flag and a union holding either
the rbtree (rb_root + rwlock) or rhashtable state:

  struct simple_xattrs {
      bool use_rhashtable;
      union {
          struct { struct rb_root rb_root; rwlock_t lock; };
          struct rhashtable ht;
      };
  };

simple_xattrs_init() continues to set up the rbtree path for existing
embedded-struct callers.

Add simple_xattrs_alloc() which dynamically allocates a simple_xattrs
and initializes the rhashtable path. This is the entry point for
consumers switching to pointer-based lazy allocation.

The five core functions (get, set, list, add, free) dispatch based on
the use_rhashtable flag.

Existing callers continue to use the rbtree path unchanged. As each
consumer is converted it will switch to simple_xattrs_alloc() and the
rhashtable path. Once all consumers are converted a follow-up patch
will remove the rbtree code.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-2-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Reviewed-by: Jan Kara 
Signed-off-by: Christian Brauner

xattr: add rcu_head and rhash_head to struct simple_xattr

2026-02-23T12:06:38+00:00

In preparation for converting simple_xattrs from rbtree to rhashtable,
add rhash_head and rcu_head members to struct simple_xattr. The
rhashtable implementation will use rhash_head for hash table linkage
and RCU-based lockless reads, requiring that replaced or removed xattr
entries be freed via call_rcu() rather than immediately.

Add simple_xattr_free_rcu() which schedules RCU-deferred freeing of an
xattr entry.  This will be used by callers of simple_xattr_set() once
they switch to the rhashtable-based xattr store.

No functional changes.

Link: https://patch.msgid.link/20260216-work-xattr-socket-v1-1-c2efa4f74cb7@kernel.org
Acked-by: Darrick J. Wong 
Signed-off-by: Christian Brauner