linux-kernel - [PATCH v3 08/21] fast_dput(): new rules for refcount

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Message-Id: <20231124060422.576198-8-viro@zeniv.linux.org.uk>
Date:   Fri, 24 Nov 2023 06:04:09 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     linux-fsdevel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christian Brauner <brauner@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 08/21] fast_dput(): new rules for refcount

By now there is only one place in entire fast_dput() where we return
false; that happens after refcount had been decremented and found (under
->d_lock) to be zero.  In that case, just prior to returning false to
caller, fast_dput() forcibly changes the refcount from 0 to 1.

Lift that resetting refcount to 1 into the callers; later in the series
it will be massaged out of existence.

Reviewed-by: Christian Brauner <brauner@...nel.org>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/dcache.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 9edabc7e2e64..a00e9ba22480 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -847,13 +847,6 @@ static inline bool fast_dput(struct dentry *dentry)
 		spin_unlock(&dentry->d_lock);
 		return true;
 	}
-
-	/*
-	 * Re-get the reference we optimistically dropped. We hold the
-	 * lock, and we just tested that it was zero, so we can just
-	 * set it to 1.
-	 */
-	dentry->d_lockref.count = 1;
 	return false;
 }
 
@@ -896,6 +889,7 @@ void dput(struct dentry *dentry)
 		}
 
 		/* Slow case: now with the dentry lock held */
+		dentry->d_lockref.count = 1;
 		rcu_read_unlock();
 
 		if (likely(retain_dentry(dentry))) {
@@ -930,6 +924,7 @@ void dput_to_list(struct dentry *dentry, struct list_head *list)
 		return;
 	}
 	rcu_read_unlock();
+	dentry->d_lockref.count = 1;
 	if (!retain_dentry(dentry))
 		__dput_to_list(dentry, list);
 	spin_unlock(&dentry->d_lock);
-- 
2.39.2