Messages in this thread | | | Date | Sat, 12 Mar 2016 22:39:59 +0800 | Subject | Re: e827091cb1 "block: merge: get the 1st and last bvec via helpers" broken | From | Ming Lei <> |
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On Sat, Mar 12, 2016 at 10:36 PM, Kent Overstreet <kent.overstreet@gmail.com> wrote: > 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.
Exactly!
> > I would still strongly suggest reverting the patch for 4.5 and resubmitting > during the next merge window.
I am fine with either way, and I will prepare one patch and let Jens decide.
thanks, Ming Lei
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