linux-kernel - [PATCH 4/5] ext4: Replace lock/unlock_super() with an explicit lock for the orphan list

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Message-Id: <1240717765-16572-5-git-send-email-tytso@mit.edu>
Date:	Sat, 25 Apr 2009 23:49:24 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	Theodore Ts'o <tytso@....edu>
Subject: [PATCH 4/5] ext4: Replace lock/unlock_super() with an explicit lock for the orphan list

Use a separate lock to protect the orphan list, so we can stop
overloading the use of lock_super().

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/ext4/ext4_sb.h |    1 +
 fs/ext4/namei.c   |   20 +++++++++++---------
 fs/ext4/super.c   |    1 +
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 57b71fe..4bda2f7 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -71,6 +71,7 @@ struct ext4_sb_info {
 	struct inode *s_journal_inode;
 	struct journal_s *s_journal;
 	struct list_head s_orphan;
+	struct mutex s_orphan_lock;
 	unsigned long s_commit_interval;
 	u32 s_max_batch_time;
 	u32 s_min_batch_time;
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 22098e1..8018e49 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1997,7 +1997,7 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
 	if (!ext4_handle_valid(handle))
 		return 0;
 
-	lock_super(sb);
+	mutex_lock(&EXT4_SB(sb)->s_orphan_lock);
 	if (!list_empty(&EXT4_I(inode)->i_orphan))
 		goto out_unlock;
 
@@ -2006,9 +2006,13 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
 
 	/* @@@ FIXME: Observation from aviro:
 	 * I think I can trigger J_ASSERT in ext4_orphan_add().  We block
-	 * here (on lock_super()), so race with ext4_link() which might bump
+	 * here (on s_orphan_lock), so race with ext4_link() which might bump
 	 * ->i_nlink. For, say it, character device. Not a regular file,
 	 * not a directory, not a symlink and ->i_nlink > 0.
+	 *
+	 * tytso, 4/25/2009: I'm not sure how that could happen;
+	 * shouldn't the fs core protect us from these sort of
+	 * unlink()/link() races?
 	 */
 	J_ASSERT((S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
 		  S_ISLNK(inode->i_mode)) || inode->i_nlink == 0);
@@ -2045,7 +2049,7 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
 	jbd_debug(4, "orphan inode %lu will point to %d\n",
 			inode->i_ino, NEXT_ORPHAN(inode));
 out_unlock:
-	unlock_super(sb);
+	mutex_unlock(&EXT4_SB(sb)->s_orphan_lock);
 	ext4_std_error(inode->i_sb, err);
 	return err;
 }
@@ -2066,11 +2070,9 @@ int ext4_orphan_del(handle_t *handle, struct inode *inode)
 	if (!ext4_handle_valid(handle))
 		return 0;
 
-	lock_super(inode->i_sb);
-	if (list_empty(&ei->i_orphan)) {
-		unlock_super(inode->i_sb);
-		return 0;
-	}
+	mutex_lock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
+	if (list_empty(&ei->i_orphan))
+		goto out;
 
 	ino_next = NEXT_ORPHAN(inode);
 	prev = ei->i_orphan.prev;
@@ -2120,7 +2122,7 @@ int ext4_orphan_del(handle_t *handle, struct inode *inode)
 out_err:
 	ext4_std_error(inode->i_sb, err);
 out:
-	unlock_super(inode->i_sb);
+	mutex_unlock(&EXT4_SB(inode->i_sb)->s_orphan_lock);
 	return err;
 
 out_brelse:
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 176d43f..c23e82c 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2623,6 +2623,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	sb->dq_op = &ext4_quota_operations;
 #endif
 	INIT_LIST_HEAD(&sbi->s_orphan); /* unlinked but open files */
+	mutex_init(&sbi->s_orphan_lock);
 
 	sb->s_root = NULL;
 
-- 
1.5.6.3

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