On Mon, Jan 20, 2020 at 08:07:21AM +0000, Al Viro wrote: > > > I hadn't checked ->d_compare() instances for a while; somebody needs to > > > do that again, by the look of it. The above definitely is broken; > > > no idea how many other instaces had grown such bugs... > > > > f2fs one also has the same bug. Anyway, I'm going down right now, will > > check the rest tomorrow morning... > > We _probably_ can get away with just checking that inode for NULL and > buggering off if it is (->d_seq mismatch is guaranteed in that case), > but I suspect that we might need READ_ONCE() on both dereferences. > I hate memory barriers... FWIW, other instances seem to be OK; HFS+ one might or might not be OK in the face of concurrent rename (wrong result in that case is no problem; oops would be), but it doesn't play silly buggers with pointer-chasing. ext4 and f2fs do, and ->d_compare() is broken in both of them.
