linux-kernel - [PATCH] ufs: fix deadlocks after mutex merge

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Date:	Tue,  2 Sep 2014 02:30:24 +0400
From:	Alexey Khoroshilov <khoroshilov@...ras.ru>
To:	Evgeniy Dushistov <dushistov@...l.ru>
Cc:	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org
Subject: [PATCH] ufs: fix deadlocks after mutex merge

Commit 0244756edc4b ("ufs: sb mutex merge + mutex_destroy") introduces
deadlocks in ufs_new_inode() and ufs_free_inode() that call lock_ufs()
being already invoked with mutex held.

ufs_free_inode() is always invoked with mutex locked, while
ufs_new_inode() is called with mutex locked two times of four.

The patch proposes to resolve the issue by agreement to call
ufs_new_inode() and ufs_free_inode() with mutex unheld.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
---
 fs/ufs/inode.c |  7 ++-----
 fs/ufs/namei.c | 14 ++++++--------
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/fs/ufs/inode.c b/fs/ufs/inode.c
index 7c580c97990e..be7d42c7d938 100644
--- a/fs/ufs/inode.c
+++ b/fs/ufs/inode.c
@@ -902,9 +902,6 @@ void ufs_evict_inode(struct inode * inode)
 	invalidate_inode_buffers(inode);
 	clear_inode(inode);
 
-	if (want_delete) {
-		lock_ufs(inode->i_sb);
-		ufs_free_inode (inode);
-		unlock_ufs(inode->i_sb);
-	}
+	if (want_delete)
+		ufs_free_inode(inode);
 }
diff --git a/fs/ufs/namei.c b/fs/ufs/namei.c
index 90d74b8f8eba..2df62a73f20c 100644
--- a/fs/ufs/namei.c
+++ b/fs/ufs/namei.c
@@ -126,12 +126,12 @@ static int ufs_symlink (struct inode * dir, struct dentry * dentry,
 	if (l > sb->s_blocksize)
 		goto out_notlocked;
 
-	lock_ufs(dir->i_sb);
 	inode = ufs_new_inode(dir, S_IFLNK | S_IRWXUGO);
 	err = PTR_ERR(inode);
 	if (IS_ERR(inode))
-		goto out;
+		goto out_notlocked;
 
+	lock_ufs(dir->i_sb);
 	if (l > UFS_SB(sb)->s_uspi->s_maxsymlinklen) {
 		/* slow symlink */
 		inode->i_op = &ufs_symlink_inode_operations;
@@ -181,13 +181,9 @@ static int ufs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
 	struct inode * inode;
 	int err;
 
-	lock_ufs(dir->i_sb);
-	inode_inc_link_count(dir);
-
 	inode = ufs_new_inode(dir, S_IFDIR|mode);
-	err = PTR_ERR(inode);
 	if (IS_ERR(inode))
-		goto out_dir;
+		return PTR_ERR(inode);
 
 	inode->i_op = &ufs_dir_inode_operations;
 	inode->i_fop = &ufs_dir_operations;
@@ -195,6 +191,9 @@ static int ufs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
 
 	inode_inc_link_count(inode);
 
+	lock_ufs(dir->i_sb);
+	inode_inc_link_count(dir);
+
 	err = ufs_make_empty(inode, dir);
 	if (err)
 		goto out_fail;
@@ -212,7 +211,6 @@ out_fail:
 	inode_dec_link_count(inode);
 	inode_dec_link_count(inode);
 	iput (inode);
-out_dir:
 	inode_dec_link_count(dir);
 	unlock_ufs(dir->i_sb);
 	goto out;
-- 
1.9.1

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