Hi, On 27.05.2014 13:24, Maurizio Lombardi wrote: > On Tue, May 27, 2014 at 10:43:59AM +0200, Maurizio Lombardi wrote: > > > > But now I'm suspicious of this part of commit 3979ef4dcf: > > > > failed: > > bvec->bv_page = NULL; > > bvec->bv_len = 0; > > bvec->bv_offset = 0; > > bio->bi_vcnt--; <---------------- > > blk_recount_segments(q, bio); > > return 0; > > > > Is decreasing bi_vcnt sufficient to guarantee that blk_recount_segments() > > recalculates the correct number of physical segments? > > Looking at the __blk_recalc_rq_segments() it appears it may not be the case. > > > > The question is how can we restore the correct number of physical segments > > in case > > of failure without breaking anything... > > If my hypothesis is correct, the following patch should trigger a kernel > panic, > Jet Chen, can you try it and let me know whether the BUG_ON is hit or not?
I was also able to reproduce this bug just as reported by Jet Chen, and now I think I've found out a solution. I'll send out a patch. Regards, Dongsu > diff --git a/block/bio.c b/block/bio.c > index 0443694..763868f 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -701,6 +701,7 @@ static int __bio_add_page(struct request_queue *q, struct > bio *bio, struct page > unsigned int max_sectors) > { > int retried_segments = 0; > + unsigned int phys_segments_orig; > struct bio_vec *bvec; > > /* > @@ -751,6 +752,9 @@ static int __bio_add_page(struct request_queue *q, struct > bio *bio, struct page > if (bio->bi_vcnt >= bio->bi_max_vecs) > return 0; > > + blk_recount_segments(q, bio); > + phys_segments_orig = bio->bi_phys_segments; > + > /* > * setup the new entry, we might clear it again later if we > * cannot add the page > @@ -811,6 +815,7 @@ static int __bio_add_page(struct request_queue *q, struct > bio *bio, struct page > bvec->bv_offset = 0; > bio->bi_vcnt--; > blk_recount_segments(q, bio); > + BUG_ON(phys_segments_orig != bio->bi_phys_segments); > return 0; > } > > > Regards, > Maurizio Lombardi > -- > 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/ -- 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/