fs: use kmem_cache_create_rcu()

Switch to the new kmem_cache_create_rcu() helper which allows us to use
a custom free pointer offset avoiding the need to have an external free
pointer which would grow struct file behind our backs.

Link: https://lore.kernel.org/r/20240828-work-kmem_cache-rcu-v3-3-5460bc1f09f6@kernel.org
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/file_table.c

@@ -511,9 +511,9 @@ EXPORT_SYMBOL(__fput_sync);
 
 void __init files_init(void)
 {
-	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
-				SLAB_TYPESAFE_BY_RCU | SLAB_HWCACHE_ALIGN |
-				SLAB_PANIC | SLAB_ACCOUNT, NULL);
+	filp_cachep = kmem_cache_create_rcu("filp", sizeof(struct file),
+				offsetof(struct file, f_freeptr),
+				SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 }
 

include/linux/fs.h

@@ -1011,6 +1011,7 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
  * @f_task_work: task work entry point
  * @f_llist: work queue entrypoint
  * @f_ra: file's readahead state
+ * @f_freeptr: Pointer used by SLAB_TYPESAFE_BY_RCU file cache (don't touch.)
  */
 struct file {
 	atomic_long_t			f_count;
@@ -1042,6 +1043,7 @@ struct file {
 		struct callback_head	f_task_work;
 		struct llist_node	f_llist;
 		struct file_ra_state	f_ra;
+		freeptr_t		f_freeptr;
 	};
 	/* --- cacheline 3 boundary (192 bytes) --- */
 } __randomize_layout