Re: [announce] vfs-scale git tree update

[Linus Torvalds]

On Tue, Jan 11, 2011 at 8:34 AM, Alex Elder <aelder@xxxxxxx> wrote:
>
> FYI, when using this code, as merged by Linus, I hit the
> BUG_ON() at the beginning of d_set_d_op() when it's called
> by autofs4_dir_mkdir().  I managed to work around it by
> just commenting out those BUG_ON() calls but it's something
> that ought to get addressed properly.

Yeah, removing the BUG_ON() isn't the right thing to do - it means
that autofs4 is obviously setting the dentry ops twice for the same
dentry.

Possibly the thing could be relaxed to allow setting the _same_ d_op
pointer, ie do something like

   if (dentry->d_op == op)
      return;

at the top of that function. But looking at it, I don't think that
fixes the autofs4 issue.

The fact that autofs4 does "d_add()" before it sets the d_ops (or
other dentry state, for that matter) looks a bit scary. To me that
smells like it might get a  dentry lookup hit before it's actually
fully done.

Does it make any difference if you move the various d_add() calls down
to the end of the functions to when the "dentry" has really been
instantiated?

                      Linus
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