linux-kernel - [PATCH] NFS: Correct timing for assigning access cache timestamp

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Message-Id: <20230308080327.33906-1-chengen.du@canonical.com>
Date:   Wed,  8 Mar 2023 16:03:27 +0800
From:   Chengen Du <chengen.du@...onical.com>
To:     trond.myklebust@...merspace.com
Cc:     anna@...nel.org, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chengen Du <chengen.du@...onical.com>
Subject: [PATCH] NFS: Correct timing for assigning access cache timestamp

When the user's login time is newer than the cache's timestamp,
the original entry in the RB-tree will be replaced by a new entry.
Currently, the timestamp is only set if the entry is not found in
the RB-tree, which can cause the timestamp to be undefined when
the entry exists. This may result in a significant increase in
ACCESS operations if the timestamp is set to zero.

Signed-off-by: Chengen Du <chengen.du@...onical.com>
---
 fs/nfs/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index a41c3ee4549c..6fbcbb8d6587 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -3089,7 +3089,6 @@ static void nfs_access_add_rbtree(struct inode *inode,
 		else
 			goto found;
 	}
-	set->timestamp = ktime_get_ns();
 	rb_link_node(&set->rb_node, parent, p);
 	rb_insert_color(&set->rb_node, root_node);
 	list_add_tail(&set->lru, &nfsi->access_cache_entry_lru);
@@ -3114,6 +3113,7 @@ void nfs_access_add_cache(struct inode *inode, struct nfs_access_entry *set,
 	cache->fsgid = cred->fsgid;
 	cache->group_info = get_group_info(cred->group_info);
 	cache->mask = set->mask;
+	cache->timestamp = ktime_get_ns();
 
 	/* The above field assignments must be visible
 	 * before this item appears on the lru.  We cannot easily
-- 
2.37.2