In ecryptfs_destroy_inode(), inode_info->lower_file_mutex is locked,
and just after the mutex is unlocked, the code does:

 	kmem_cache_free(ecryptfs_inode_info_cache, inode_info);

This means that if another context could possibly try to take the same
mutex as ecryptfs_destroy_inode(), then it could end up getting the
mutex just before the data structure containing the mutex is freed.
So any such use would be an obvious use-after-free bug (catchable with
slab poisoning or mutex debugging), and therefore the locking in
ecryptfs_destroy_inode() is not needed and can be dropped.

Similarly, in ecryptfs_destroy_crypt_stat(), crypt_stat->keysig_list_mutex
is locked, and then the mutex is unlocked just before the code does:

 	memset(crypt_stat, 0, sizeof(struct ecryptfs_crypt_stat));

Therefore taking this mutex is similarly not necessary.

Removing this locking fixes false-positive lockdep reports such as the
following (and they are false-positives for exactly the same reason
that the locking is not needed):

=================================
[ INFO: inconsistent lock state ]
2.6.31-2-generic #14~rbd3
---------------------------------
inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
kswapd0/323 [HC0[0]:SC0[0]:HE1:SE1] takes:
 (&inode_info->lower_file_mutex){+.+.?.}, at: [<ffffffff81210d34>] ecryptfs_destroy_inode+0x34/0x100
{RECLAIM_FS-ON-W} state was registered at:
  [<ffffffff8108c02c>] mark_held_locks+0x6c/0xa0
  [<ffffffff8108c10f>] lockdep_trace_alloc+0xaf/0xe0
  [<ffffffff81125a51>] kmem_cache_alloc+0x41/0x1a0
  [<ffffffff8113117a>] get_empty_filp+0x7a/0x1a0
  [<ffffffff8112dd46>] dentry_open+0x36/0xc0
  [<ffffffff8121a36c>] ecryptfs_privileged_open+0x5c/0x2e0
  [<ffffffff81210283>] ecryptfs_init_persistent_file+0xa3/0xe0
  [<ffffffff8120e838>] ecryptfs_lookup_and_interpose_lower+0x278/0x380
  [<ffffffff8120f97a>] ecryptfs_lookup+0x12a/0x250
  [<ffffffff8113930a>] real_lookup+0xea/0x160
  [<ffffffff8113afc8>] do_lookup+0xb8/0xf0
  [<ffffffff8113b518>] __link_path_walk+0x518/0x870
  [<ffffffff8113bd9c>] path_walk+0x5c/0xc0
  [<ffffffff8113be5b>] do_path_lookup+0x5b/0xa0
  [<ffffffff8113bfe7>] user_path_at+0x57/0xa0
  [<ffffffff811340dc>] vfs_fstatat+0x3c/0x80
  [<ffffffff8113424b>] vfs_stat+0x1b/0x20
  [<ffffffff81134274>] sys_newstat+0x24/0x50
  [<ffffffff81013132>] system_call_fastpath+0x16/0x1b
  [<ffffffffffffffff>] 0xffffffffffffffff
irq event stamp: 7811
hardirqs last  enabled at (7811): [<ffffffff810c037f>] call_rcu+0x5f/0x90
hardirqs last disabled at (7810): [<ffffffff810c0353>] call_rcu+0x33/0x90
softirqs last  enabled at (3764): [<ffffffff810631da>] __do_softirq+0x14a/0x220
softirqs last disabled at (3751): [<ffffffff8101440c>] call_softirq+0x1c/0x30

other info that might help us debug this:
2 locks held by kswapd0/323:
 #0:  (shrinker_rwsem){++++..}, at: [<ffffffff810f67ed>] shrink_slab+0x3d/0x190
 #1:  (&type->s_umount_key#35){.+.+..}, at: [<ffffffff811429a1>] prune_dcache+0xd1/0x1b0

stack backtrace:
Pid: 323, comm: kswapd0 Tainted: G         C 2.6.31-2-generic #14~rbd3
Call Trace:
 [<ffffffff8108ad6c>] print_usage_bug+0x18c/0x1a0
 [<ffffffff8108aff0>] ? check_usage_forwards+0x0/0xc0
 [<ffffffff8108bac2>] mark_lock_irq+0xf2/0x280
 [<ffffffff8108bd87>] mark_lock+0x137/0x1d0
 [<ffffffff81164710>] ? fsnotify_clear_marks_by_inode+0x30/0xf0
 [<ffffffff8108bee6>] mark_irqflags+0xc6/0x1a0
 [<ffffffff8108d337>] __lock_acquire+0x287/0x430
 [<ffffffff8108d585>] lock_acquire+0xa5/0x150
 [<ffffffff81210d34>] ? ecryptfs_destroy_inode+0x34/0x100
 [<ffffffff8108d2e7>] ? __lock_acquire+0x237/0x430
 [<ffffffff815526ad>] __mutex_lock_common+0x4d/0x3d0
 [<ffffffff81210d34>] ? ecryptfs_destroy_inode+0x34/0x100
 [<ffffffff81164710>] ? fsnotify_clear_marks_by_inode+0x30/0xf0
 [<ffffffff81210d34>] ? ecryptfs_destroy_inode+0x34/0x100
 [<ffffffff8129a91e>] ? _raw_spin_unlock+0x5e/0xb0
 [<ffffffff81552b36>] mutex_lock_nested+0x46/0x60
 [<ffffffff81210d34>] ecryptfs_destroy_inode+0x34/0x100
 [<ffffffff81145d27>] destroy_inode+0x87/0xd0
 [<ffffffff81146b4c>] generic_delete_inode+0x12c/0x1a0
 [<ffffffff81145832>] iput+0x62/0x70
 [<ffffffff811423c8>] dentry_iput+0x98/0x110
 [<ffffffff81142550>] d_kill+0x50/0x80
 [<ffffffff81142623>] prune_one_dentry+0xa3/0xc0
 [<ffffffff811428b1>] __shrink_dcache_sb+0x271/0x290
 [<ffffffff811429d9>] prune_dcache+0x109/0x1b0
 [<ffffffff81142abf>] shrink_dcache_memory+0x3f/0x50
 [<ffffffff810f68dd>] shrink_slab+0x12d/0x190
 [<ffffffff810f9377>] balance_pgdat+0x4d7/0x640
 [<ffffffff8104c4c0>] ? finish_task_switch+0x40/0x150
 [<ffffffff810f63c0>] ? isolate_pages_global+0x0/0x60
 [<ffffffff810f95f7>] kswapd+0x117/0x170
 [<ffffffff810777a0>] ? autoremove_wake_function+0x0/0x40
 [<ffffffff810f94e0>] ? kswapd+0x0/0x170
 [<ffffffff810773be>] kthread+0x9e/0xb0
 [<ffffffff8101430a>] child_rip+0xa/0x20
 [<ffffffff81013c90>] ? restore_args+0x0/0x30
 [<ffffffff81077320>] ? kthread+0x0/0xb0
 [<ffffffff81014300>] ? child_rip+0x0/0x20
Signed-off-by: Roland Dreier <roland@digitalvampire.org>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>