LU-16807 llite: make lsm_sem nested for ll_update_dir_depth

Lockdep is reporting:

chmod/16751 is trying to acquire lock:
 (&lli->lli_lsm_sem){++++}-{3:3}, at: ll_update_dir_depth+0x8b/0x280

but task is already holding lock:
 (&lli->lli_lsm_sem){++++}-{3:3}, at: ll_update_dir_depth+0x7b/0x280

 other info that might help us debug this:
 Possible unsafe locking scenario:

        CPU0
        ----
 lock(&lli->lli_lsm_sem);
 lock(&lli->lli_lsm_sem);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

Lockdep sees acquiring more than one lock of the same lock class
as a potential dead lock. The execption is if the locks are used
for objects that belong to a hierarchy. For our case of the
lsm_sem we do have a hierarchy since a lsm for a child directory
is related to the parent directory lsm that is being protected
as well. Create new lock classes for the lsm_sem with proper
ordering.

Change-Id: I06c890d16816b83492cbeadabde3515ee0233424
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51192
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>

diff --git a/lustre/llite/llite_lib.c b/lustre/llite/llite_lib.c
index 2054fc0..3313705 100644 (file)
--- a/lustre/llite/llite_lib.c
+++ b/lustre/llite/llite_lib.c
@@ -2939,6 +2939,11 @@ unlock_parent:
        return rc;
 }
 
+enum lsm_sem_class {
+       LSM_SEM_PARENT,
+       LSM_SEM_CHILD,
+};
+
 /**
  * Update directory depth and default LMV
  *
@@ -2965,8 +2970,8 @@ void ll_update_dir_depth_dmv(struct inode *dir, struct dentry *de)
        lli->lli_dir_depth = plli->lli_dir_depth + 1;
        if (lli->lli_default_lsm_md && lli->lli_default_lmv_set) {
                if (plli->lli_default_lsm_md) {
-                       down_read(&plli->lli_lsm_sem);
-                       down_read(&lli->lli_lsm_sem);
+                       down_read_nested(&plli->lli_lsm_sem, LSM_SEM_PARENT);
+                       down_read_nested(&lli->lli_lsm_sem, LSM_SEM_CHILD);
                        if (lsm_md_inherited(plli->lli_default_lsm_md,
                                             lli->lli_default_lsm_md))
                                lli->lli_inherit_depth =