[lustre-devel] [PATCH 13/21] lustre: llite: make lsm_sem nested for ll_update_dir_depth

[James Simmons]

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.

WC-bug-id: https://jira.whamcloud.com/browse/LU-16807
Lustre-commit: fe44198b7fb710fce ("LU-16807 llite: make lsm_sem nested for ll_update_dir_depth")
Signed-off-by: James Simmons <jsimmons at infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51192
Reviewed-by: Arshad Hussain <arshad.hussain at aeoncomputing.com>
Reviewed-by: Oleg Drokin <green at whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao at whamcloud.com>
Reviewed-by: Andreas Dilger <adilger at whamcloud.com>
---
 fs/lustre/llite/llite_lib.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/lustre/llite/llite_lib.c b/fs/lustre/llite/llite_lib.c
index afb231ecd70b..99b2982fa322 100644
--- a/fs/lustre/llite/llite_lib.c
+++ b/fs/lustre/llite/llite_lib.c
@@ -2832,6 +2832,11 @@ int ll_dir_default_lmv_inherit(struct inode *dir, struct inode *inode)
 	return rc;
 }
 
+enum lsm_sem_class {
+	LSM_SEM_PARENT,
+	LSM_SEM_CHILD,
+};
+
 /**
  * Update directory depth and default LMV
  *
@@ -2858,8 +2863,8 @@ 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 =
-- 
2.39.3