vfs: drop one lock trip in evict()

Most commonly neither I_LRU_ISOLATING nor I_SYNC are set, but the stock
kernel takes a back-to-back relock trip to check for them.

It probably can be avoided altogether, but for now massage things back
to just one lock acquire.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240813143626.1573445-1-mjguzik@gmail.comReviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/fs-writeback.c

@@ -1510,13 +1510,12 @@ static int write_inode(struct inode *inode, struct writeback_control *wbc)
  * Wait for writeback on an inode to complete. Called with i_lock held.
  * Caller must make sure inode cannot go away when we drop i_lock.
  */
-static void __inode_wait_for_writeback(struct inode *inode)
-	__releases(inode->i_lock)
-	__acquires(inode->i_lock)
+void inode_wait_for_writeback(struct inode *inode)
 {
 	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
 	wait_queue_head_t *wqh;
 
+	lockdep_assert_held(&inode->i_lock);
 	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 	while (inode->i_state & I_SYNC) {
 		spin_unlock(&inode->i_lock);
@@ -1526,16 +1525,6 @@ static void __inode_wait_for_writeback(struct inode *inode)
 	}
 }
 
-/*
- * Wait for writeback on an inode to complete. Caller must have inode pinned.
- */
-void inode_wait_for_writeback(struct inode *inode)
-{
-	spin_lock(&inode->i_lock);
-	__inode_wait_for_writeback(inode);
-	spin_unlock(&inode->i_lock);
-}
-
 /*
  * Sleep until I_SYNC is cleared. This function must be called with i_lock
  * held and drops it. It is aimed for callers not holding any inode reference
@@ -1757,7 +1746,7 @@ static int writeback_single_inode(struct inode *inode,
 		 */
 		if (wbc->sync_mode != WB_SYNC_ALL)
 			goto out;
-		__inode_wait_for_writeback(inode);
+		inode_wait_for_writeback(inode);
 	}
 	WARN_ON(inode->i_state & I_SYNC);
 	/*

fs/inode.c

@@ -507,7 +507,7 @@ static void inode_unpin_lru_isolating(struct inode *inode)
 
 static void inode_wait_for_lru_isolating(struct inode *inode)
 {
-	spin_lock(&inode->i_lock);
+	lockdep_assert_held(&inode->i_lock);
 	if (inode->i_state & I_LRU_ISOLATING) {
 		DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LRU_ISOLATING);
 		wait_queue_head_t *wqh;
@@ -518,7 +518,6 @@ static void inode_wait_for_lru_isolating(struct inode *inode)
 		spin_lock(&inode->i_lock);
 		WARN_ON(inode->i_state & I_LRU_ISOLATING);
 	}
-	spin_unlock(&inode->i_lock);
 }
 
 /**
@@ -690,6 +689,7 @@ static void evict(struct inode *inode)
 
 	inode_sb_list_del(inode);
 
+	spin_lock(&inode->i_lock);
 	inode_wait_for_lru_isolating(inode);
 
 	/*
@@ -699,6 +699,7 @@ static void evict(struct inode *inode)
 	 * the inode.  We just have to wait for running writeback to finish.
 	 */
 	inode_wait_for_writeback(inode);
+	spin_unlock(&inode->i_lock);
 
 	if (op->evict_inode) {
 		op->evict_inode(inode);