Messages in this thread | | | Date | Sat, 12 Mar 2016 05:36:12 -0900 | From | Kent Overstreet <> | Subject | Re: e827091cb1 "block: merge: get the 1st and last bvec via helpers" broken |
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On Sat, Mar 12, 2016 at 10:25:48PM +0800, Ming Lei wrote: > On Sat, 12 Mar 2016 05:02:56 -0900 > Kent Overstreet <kent.overstreet@gmail.com> wrote: > > > Here's the output of the patch below: > > > > generic/036 11s ...run fstests generic/036 at 2016-03-12 13:58:21 > > end 4096 0 ffffea0001d611c0 end2 1024 0 ffffea0001d611c0 > > len 1024 offset 0 page ffffea0001d611c0 > > KGDB: Waiting for remote debugger > > > > Your code gives a biovec with bv_len of 4096, the old code gives a biovec with > > bv_len of 1024 (and then we dump every biovec, we see that the bio had only a > > single biovec that did indeed have bv_len == 1024). > > I guess we shouldn't have optimized for the case of non-cloned bio, could you > try the following patch? > > -- > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 1e7248f..4abc129 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -267,11 +267,6 @@ static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv) > struct bvec_iter iter = bio->bi_iter; > int idx; > > - if (!bio_flagged(bio, BIO_CLONED)) { > - *bv = bio->bi_io_vec[bio->bi_vcnt - 1]; > - return; > - } > - > if (unlikely(!bio_multiple_segments(bio))) { > *bv = bio_iovec(bio); > return; > > Thanks, > Ming
Yes, that's it.
!BIO_CLONED is _not_ a guarantee that bi_size doesn't straddle the middle of a bvec - bcachefs was hitting this by bouncing a bio that had already been split (which can happen elsewhere in the kernel...) but there's other (perfectly legal) ways it can happen.
I would still strongly suggest reverting the patch for 4.5 and resubmitting during the next merge window.
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