Commit aa1d058d authored by Ian Kent's avatar Ian Kent Committed by Greg Kroah-Hartman
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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: default avatarIan Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/166606036215.13363.1288735296954908554.stgit@donald.themaw.net


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5033ac5c

fs/kernfs/inode.c

+0 −4
Original line number Diff line number Diff line
@@ -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;