On Mon, Jan 20, 2020 at 07:35:58PM +0000, Al Viro wrote: > 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. Thanks Al. I sent out fixes for this: ext4: https://lore.kernel.org/r/20200124041234.159740-1-ebiggers@xxxxxxxxxx f2fs: https://lore.kernel.org/r/20200124041549.159983-1-ebiggers@xxxxxxxxxx Note that ->d_hash() was broken too. In fact, that was much easier to reproduce. - Eric
