[PATCH] xattrr: preparation for fine-grained locking

From: Andreas Gruenbacher <agruen@suse.de>

Andrew Morton found that there is lock contention between extended
attribute operations (like reading ACLs, which `ls -l' needs to do)
and other operations on the same files. This is due to the fact that
all extended attribute syscalls take inode->i_sem before calling into
the filesystem code.

To fix this problem, this patch no longer takes inode->i_sem in the
getxattr and listxattr syscalls, and moves the lock taking code into
the file systems. (Another patch improves the locking strategy in
ext2 and ext3.)

1 files changed, 13 insertions, 2 deletions

diff --git a/fs/ext3/xattr.c b/fs/ext3/xattr.c
index 0db74f94229681..b89f8be46f0f7d 100644
--- a/fs/ext3/xattr.c
+++ b/fs/ext3/xattr.c
@@ -199,11 +199,16 @@ ext3_getxattr(struct dentry *dentry, const char *name,
 {
 	struct ext3_xattr_handler *handler;
 	struct inode *inode = dentry->d_inode;
+	ssize_t error;
 
 	handler = ext3_xattr_resolve_name(&name);
 	if (!handler)
 		return -EOPNOTSUPP;
-	return handler->get(inode, name, buffer, size);
+	down(&inode->i_sem);
+	error = handler->get(inode, name, buffer, size);
+	up(&inode->i_sem);
+
+	return error;
 }
 
 /*
@@ -214,7 +219,13 @@ ext3_getxattr(struct dentry *dentry, const char *name,
 ssize_t
 ext3_listxattr(struct dentry *dentry, char *buffer, size_t size)
 {
-	return ext3_xattr_list(dentry->d_inode, buffer, size);
+	ssize_t error;
+
+	down(&dentry->d_inode->i_sem);
+	error = ext3_xattr_list(dentry->d_inode, buffer, size);
+	up(&dentry->d_inode->i_sem);
+
+	return error;
 }
 
 /*