ecryptfs: Fix inodes not being evicted until unmount

On asynchronous base filesystems like NFS, eCryptFS leaves inodes for deleted files in the cache until unmounting. Change call in ecryptfs_do_unlink() from set_nlink() to drop_nlink() in order to reliably evict inodes from the cache even on top of NFS.

---
 fs/ecryptfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e23752d..f7594b6 100644
@@ -147,7 +147,7 @@ static int ecryptfs_do_unlink(struct inode *dir, struct dentry *dentry,
 		goto out_unlock;
 	}
 	fsstack_copy_attr_times(dir, lower_dir_inode);
-	set_nlink(inode, ecryptfs_inode_to_lower(inode)->i_nlink);
+	drop_nlink(inode);
 	inode->i_ctime = dir->i_ctime;
 out_unlock:
 	dput(lower_dentry);

2.7.4

Steps to reproduce issue:
Mount nfs
Inside the nfs mount, create back and front directories for ecryptfs Use ecryptfs to mount one directory onto the other
Create a few files inside the ecryptfs mount
Set ftrace to monitor ecryptfs_do_unlink() and ecryptfs_evict_inode() Delete files
Unmount ecryptfs

ftrace output before patch:
# tracer: function_graph
#
# CPU DURATION FUNCTION CALLS
# | | | | | | |

 1)               |  /* Tracing enabled */
 1)               |  /* Writing to files */
 1)               |  /* Unlinking first file */
 0) * 27804.34 us |  ecryptfs_do_unlink();
 1)               |  /* rm'ing second file */

------------------------------------------
0) unlink-1384 => rm-1385
------------------------------------------

 0) * 32828.63 us |  ecryptfs_do_unlink();
 1)               |  /* Unmounting eCryptFS */

------------------------------------------
1) trace-a-1365 => umount-1387
------------------------------------------

 1)   2.408 us    |  ecryptfs_evict_inode();
 1)   8.914 us    |  ecryptfs_evict_inode();
 1)   3.344 us    |  ecryptfs_evict_inode();

ftrace output after patch:
# tracer: function_graph
#
# CPU DURATION FUNCTION CALLS
# | | | | | | |

 0)               |  /* Tracing enabled */
 0)               |  /* Writing to files */
 0)               |  /* Unlinking first file */
 1) * 24728.81 us |  ecryptfs_do_unlink();
 1) + 20.923 us   |  ecryptfs_evict_inode();
 0)               |  /* rm'ing second file */

------------------------------------------
1) unlink-1333 => rm-1334
------------------------------------------

 1) * 41093.71 us |  ecryptfs_do_unlink();
 1) + 11.384 us   |  ecryptfs_evict_inode();
 0)               |  /* Unmounting eCryptFS */

------------------------------------------
0) trace-a-1314 => umount-1336
------------------------------------------

0) 2.986 us | ecryptfs_evict_inode();