[PATCH -vfs] proc: don't maintain sizeof(struct proc_dir_entry)

[Alexey Dobriyan]

Automatically cap sizeof(struct proc_dir_entry) at 192/128 bytes or
256/192 bytes if spinlock debugging/lockdep is enabled.

Signed-off-by: Alexey Dobriyan <adobri...@gmail.com>
---

 fs/proc/generic.c  |    2 +-
 fs/proc/inode.c    |    5 +++--
 fs/proc/internal.h |   10 ++++++----
 3 files changed, 10 insertions(+), 7 deletions(-)

--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -410,7 +410,7 @@ static struct proc_dir_entry *__proc_create(struct 
proc_dir_entry **parent,
        if (!ent)
                goto out;
 
-       if (qstr.len + 1 <= sizeof(ent->inline_name)) {
+       if (qstr.len + 1 <= SIZEOF_PDE_INLINE_NAME) {
                ent->name = ent->inline_name;
        } else {
                ent->name = kmalloc(qstr.len + 1, GFP_KERNEL);
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -105,9 +105,10 @@ void __init proc_init_kmemcache(void)
                kmem_cache_create("pde_opener", sizeof(struct pde_opener), 0,
                                  SLAB_ACCOUNT|SLAB_PANIC, NULL);
        proc_dir_entry_cache = kmem_cache_create_usercopy(
-               "proc_dir_entry", sizeof(struct proc_dir_entry), 0, SLAB_PANIC,
+               "proc_dir_entry", SIZEOF_PDE, 0, SLAB_PANIC,
                offsetof(struct proc_dir_entry, inline_name),
-               sizeof_field(struct proc_dir_entry, inline_name), NULL);
+               SIZEOF_PDE_INLINE_NAME, NULL);
+       BUILD_BUG_ON(sizeof(struct proc_dir_entry) >= SIZEOF_PDE);
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -61,13 +61,15 @@ struct proc_dir_entry {
        char *name;
        umode_t mode;
        u8 namelen;
+       char inline_name[];
+} __randomize_layout;
+
 #ifdef CONFIG_64BIT
-#define SIZEOF_PDE_INLINE_NAME (192-155)
+#define SIZEOF_PDE     (sizeof(spinlock_t) == 4 ? 192 : 256)
 #else
-#define SIZEOF_PDE_INLINE_NAME (128-95)
+#define SIZEOF_PDE     (sizeof(spinlock_t) == 4 ? 128 : 192)
 #endif
-       char inline_name[SIZEOF_PDE_INLINE_NAME];
-} __randomize_layout;
+#define SIZEOF_PDE_INLINE_NAME (SIZEOF_PDE - sizeof(struct proc_dir_entry))
 
 extern struct kmem_cache *proc_dir_entry_cache;
 void pde_free(struct proc_dir_entry *pde);