Hi Eric! On Wed, Jan 15, 2014 at 07:07:26PM -0800, Eric Dumazet wrote: > On Thu, 2014-01-16 at 00:23 +0100, Daniel Borkmann wrote: > > > Also, reciprocal_value() and reciprocal_divide() always return 0 > > for divisions by 1. This is a bit worrisome as those functions > > also get used in mm/slab.c and lib/flex_array.c, apparently for > > index calculation to access array slots. > > Hi Daniel > > This off-by-one limitation is a known one, > and mm/slab.c does not have an issue with it because : > > - Minimal object size is not 1 byte, but 8 (or maybe 4) > - We always divide a multiple of the divisor, > so there is no off-by-one effect. > > Little attached prog does a brute force check if needed. > > So far, the only relevant issue was about BPF, and a better > documentation of reciprocal_divide() use cases. > > (I let Jesse comment on the flex_array case) > > I am unsure we want to 'fix' things, we tried hard in the past to avoid > divides, so the ones we use are usually because the divisor is not > constant, so the reciprocal doesn't help. > > (BPF is fixed in David tree) > > Thanks !
You are right, we rewrite that part. The text is still from the first commit message where we did no full impact analysis. ;) Thanks, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
