kernfs: dont take i_lock on inode attr read

The kernfs write lock is held when the kernfs node inode attributes
are updated. Therefore, when either kernfs_iop_getattr() or
kernfs_iop_permission() are called the kernfs node inode attributes
won't change.

Consequently concurrent kernfs_refresh_inode() calls always copy the
same values from the kernfs node.

So there's no need to take the inode i_lock to get consistent values
for generic_fillattr() and generic_permission(), the kernfs read lock
is sufficient.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/166606036215.13363.1288735296954908554.stgit@donald.themaw.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index 3d783d80f5daab2d1b8cb8681aa39ef5ca10d9fd..74f3453f4639f4276c3841fd468aa09e92c59e59 100644 (file)
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -190,10 +190,8 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns,
        struct kernfs_root *root = kernfs_root(kn);
 
        down_read(&root->kernfs_rwsem);
-       spin_lock(&inode->i_lock);
        kernfs_refresh_inode(kn, inode);
        generic_fillattr(&init_user_ns, inode, stat);
-       spin_unlock(&inode->i_lock);
        up_read(&root->kernfs_rwsem);
 
        return 0;
@@ -288,10 +286,8 @@ int kernfs_iop_permission(struct user_namespace *mnt_userns,
        root = kernfs_root(kn);
 
        down_read(&root->kernfs_rwsem);
-       spin_lock(&inode->i_lock);
        kernfs_refresh_inode(kn, inode);
        ret = generic_permission(&init_user_ns, inode, mask);
-       spin_unlock(&inode->i_lock);
        up_read(&root->kernfs_rwsem);
 
        return ret;