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Subject[PATCH 1/2] kernfs: dont take i_lock on inode attr read
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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.

Signed-off-by: Ian Kent <raven@themaw.net>
---
fs/kernfs/inode.c | 4 ----
1 file changed, 4 deletions(-)

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index 3d783d80f5da..74f3453f4639 100644
--- 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;

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