Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> Is the rmb() really needed?
>
> Take this code from fs/namei.c for example:
>
> inode = next.dentry->d_inode;
> if (!inode)
> goto out_dput;
>
> if (inode->i_op->follow_link) {
>
> It happily dereferences dentry->d_inode without a barrier after
> checking it for non-null, while that d_inode might have just been
> initialized on another CPU with a freshly created inode. There's
> absolutely no synchornization with that on this side.
Perhaps it's not necessary; once set, how likely is i_op to be changed once
I_NEW is cleared?
> Isn't the fact that we check the pointer for being non-null (together
> with locking/barrier on the other side) enough to ensure that it's
> safe to dereference it?
It's possible that since there's a dependency between the variables on the
reading CPU that the barrier is not required.
I think I have to refer that question to Paul.
David
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