On Wed, Mar 15, 2017 at 7:32 AM, Bob Peterson <rpete...@redhat.com> wrote:
>
> Andreas Gruenbacher (1):
> gfs2: Avoid alignment hole in struct lm_lockname
So I've pulled this because I think it fixes a real bug, but honestly
I think it's the wrong fix.
Marking that lm_lockname structure "packed, aligned(4)" means that the
compiler will now think that the 64-bit fields in it may be unaligned
- including on architectures where that can be very expensive and the
compiler now might generate stupid unaligned instruction sequences to
load those values.
So the *correct* fix, I think, would have been:
- add a comment about not having holes in the struct due to the hashing
- sort the fields by size (so "ln_number" first, then "ln_sbd", then "ln_type")
- use offsetofend(struct lm_lockname, ln_type) instead of sizeof() when hashing
which avoids the "possibly generate garbage code" issue due to the
quick-and-dirty one-liner approach.
Hmm?
Linus
