linux-ext4 - [RFC PATCH 5/6] ext4: Search for an inode to update under the RCU lock if we can

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Message-ID: <155559640398.21702.15109713276957584268.stgit@warthog.procyon.org.uk>
Date:   Thu, 18 Apr 2019 15:06:44 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, dhowells@...hat.com,
        linux-afs@...ts.infradead.org, linux-ext4@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 5/6] ext4: Search for an inode to update under the RCU
 lock if we can

When we're updating timestamps in an inode, search for that inode under RCU
conditions to avoid holding the icache lock if we can.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: "Theodore Ts'o" <tytso@....edu>
cc: Andreas Dilger <adilger.kernel@...ger.ca>
cc: linux-ext4@...r.kernel.org
---

 fs/ext4/inode.c |   41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b32a57bc5d5d..13e928ae70e5 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5144,21 +5144,23 @@ static int ext4_inode_blocks_set(handle_t *handle,
 	return 0;
 }
 
-struct other_inode {
-	unsigned long		orig_ino;
-	struct ext4_inode	*raw_inode;
-};
-
-static int other_inode_match(struct inode * inode, unsigned long ino,
-			     void *data)
+static void __ext4_update_other_inode_time(struct super_block *sb,
+					   unsigned long orig_ino,
+					   unsigned long ino,
+					   struct ext4_inode *raw_inode)
 {
-	struct other_inode *oi = (struct other_inode *) data;
+	struct inode *inode;
+
+	inode = find_inode_by_ino_rcu(sb, ino);
+	if (!inode)
+		return;
 
 	if ((inode->i_ino != ino) ||
 	    (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
 			       I_DIRTY_INODE)) ||
 	    ((inode->i_state & I_DIRTY_TIME) == 0))
-		return 0;
+		return;
+
 	spin_lock(&inode->i_lock);
 	if (((inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
 				I_DIRTY_INODE)) == 0) &&
@@ -5169,16 +5171,15 @@ static int other_inode_match(struct inode * inode, unsigned long ino,
 		spin_unlock(&inode->i_lock);
 
 		spin_lock(&ei->i_raw_lock);
-		EXT4_INODE_SET_XTIME(i_ctime, inode, oi->raw_inode);
-		EXT4_INODE_SET_XTIME(i_mtime, inode, oi->raw_inode);
-		EXT4_INODE_SET_XTIME(i_atime, inode, oi->raw_inode);
-		ext4_inode_csum_set(inode, oi->raw_inode, ei);
+		EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
+		EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
+		EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
+		ext4_inode_csum_set(inode, raw_inode, ei);
 		spin_unlock(&ei->i_raw_lock);
-		trace_ext4_other_inode_update_time(inode, oi->orig_ino);
-		return -1;
+		trace_ext4_other_inode_update_time(inode, orig_ino);
+		return;
 	}
 	spin_unlock(&inode->i_lock);
-	return -1;
 }
 
 /*
@@ -5188,24 +5189,24 @@ static int other_inode_match(struct inode * inode, unsigned long ino,
 static void ext4_update_other_inodes_time(struct super_block *sb,
 					  unsigned long orig_ino, char *buf)
 {
-	struct other_inode oi;
 	unsigned long ino;
 	int i, inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
 	int inode_size = EXT4_INODE_SIZE(sb);
 
-	oi.orig_ino = orig_ino;
 	/*
 	 * Calculate the first inode in the inode table block.  Inode
 	 * numbers are one-based.  That is, the first inode in a block
 	 * (assuming 4k blocks and 256 byte inodes) is (n*16 + 1).
 	 */
 	ino = ((orig_ino - 1) & ~(inodes_per_block - 1)) + 1;
+	rcu_read_lock();
 	for (i = 0; i < inodes_per_block; i++, ino++, buf += inode_size) {
 		if (ino == orig_ino)
 			continue;
-		oi.raw_inode = (struct ext4_inode *) buf;
-		(void) find_inode_nowait(sb, ino, other_inode_match, &oi);
+		__ext4_update_other_inode_time(sb, orig_ino, ino,
+					       (struct ext4_inode *)buf);
 	}
+	rcu_read_unlock();
 }
 
 /*