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Date: Mon, 18 Jun 2001 12:55:21 -0400 (EDT)
From: Alexander Viro <viro@math.psu.edu>
To: Richard Gooch <rgooch@ras.ucalgary.ca>
cc: linux-kernel@vger.kernel.org, devfs-announce-list@vindaloo.ras.ucalgary.ca
Subject: Re: [PATCH] devfs v181 available
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On Mon, 18 Jun 2001, Richard Gooch wrote:

> > Irrelevant. BKL provides an exclusion only on non-blocking areas.
> 
> Yeah, I know all that.

So what the hell are you talking about?

> > _Moved_ them there from the callers of these functions. And AFAICS
> > you do need BKL for get_devfs_entry_...(); otherwise relocation of
> > the table will be able to screw you inside of that function. Now, it
> > will merrily screw you anyway in a lot of places, but that's another
> > story.
> 
> OK, so it was another global change.

Moving BKL into the ->readlink() and ->follow_link()? Sure, it was a global
change. About a year ago.

> Question: assuming data fed to vfs_follow_link() is "safe", does it
            ^^^^^^^^
> need the BKL? I can see that vfs_readlink() obviously doesn't need
> it. From reading Documentation/filesystems/Locking I suspect it
> doesn't need the BKL, but the way I read it says "follow_link() method
> does not *have* the BKL already". But that doesn't explicitely say
> whether vfs_follow_link() needs it.

vfs_follow_link() doesn't need it. Moreover, if data fed to it is unsafe
without BKL, you are screwed even if you take BKL. So assumption above
is bogus - you _never_ need BKL on that call.