linux-kernel - Re: reorganized struct inode results in unaligned accesses

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Message-ID: <BANLkTiktb6GS7fcHRRgC=bHJjz8k0hVmPw@mail.gmail.com>
Date:	Sun, 19 Jun 2011 09:51:24 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Meelis Roos <mroos@...ux.ee>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	sparclinux@...r.kernel.org
Subject: Re: reorganized struct inode results in unaligned accesses

On Sun, Jun 19, 2011 at 9:33 AM, Meelis Roos <mroos@...ux.ee> wrote:
>
> Commit 13e12d14e2dccc7995b8f15a5678a338ab4e6a8c (vfs: reorganize 'struct
> inode' layout a bit) changes i_state to be unsigned int instead of
> unsigned long. This is the cause of unaligned accesses on sparc64 and
> maybe others. Changing it back to unsigned long fixes the warnings but I
> did not look at the layout of the resulting struct - might leave a hole
> there.

Argh. Gaah, we acces that thing with the bit-ops when we do the
bit_waitqueue() and wait_on_bit() thing.

My bad, and apparently our type checking for the wait-on-bit stuff
isn't as tight as it should be.

Dang. I guess it needs to be made "unsigned long" again. Which is a
shame, because we only use a couple of bits from there, and "struct
inode" really is much too big already.

I do wonder why "wait_on_bit()" takes a "void *", when apparently it
can only handle "unsigned long *" entities. Maybe we could fix the
implementation to really take anything.

                  Linus
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