mm/slub: fix missing debugfs entries for caches created before sysfs init

slab_debugfs_init() creates the slab debugfs root at device initcall
time, while slab_sysfs_init() moves slab_state to FULL at late initcall
time. SLAB_STORE_USER caches created in this window miss their debugfs
entries because do_kmem_cache_create() skips debugfs_slab_add() when
slab_state <= UP. This was observed with MPTCP's request_sock_subflow_v6
cache, whose slab debugfs directory was missing.

The affected window is:

  slab_debugfs_init()
    slab_debugfs_root = debugfs_create_dir(...)
    list_for_each_entry(s, &slab_caches, list)
      debugfs_slab_add(s)

  kmem_cache_create(..., SLAB_STORE_USER, ...)
    do_kmem_cache_create()
      if (slab_state <= UP)
        return without debugfs entries

  slab_sysfs_init()
    slab_state = FULL

Initialize the debugfs root and add debugfs entries while holding
slab_mutex, walking slab_caches exactly once and handling both sysfs
and debugfs entries in the same pass. This gives the sysfs and debugfs
initialization an explicit order and prevents caches from being
created between the debugfs scan and slab_state reaching FULL.

Gate the new slab_late_init() on either sysfs or debugfs being enabled,
with the slab_kset creation and alias_list processing factored into
helpers that have empty no-sysfs variants, as suggested by Vlastimil
Babka. On slab_kset_init() failure, slab_state stays below FULL so
kmem_cache_create() keeps taking the early-boot path, matching prior
behavior.

Guard debugfs_slab_release() against an uninitialized debugfs root,
since the root is now created later and a cache may be released before
it exists.

Fixes: 1a5ad30b89b4 ("mm: slub: make slab_sysfs_init() a late_initcall")
Cc: stable@vger.kernel.org
Suggested-by: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Li Xiasong <lixiasong1@huawei.com>
Link: https://patch.msgid.link/20260729101849.3734287-1-lixiasong1@huawei.com
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

0 files changed, 0 insertions, 0 deletions