On Thu, Nov 04, 2021 at 12:11:45AM +0800, Coly Li wrote: >> fresh page for each vec, and bio_for_each_segment_all iterates page >> by page. IFF there is an offset there is proble in the surrounding >> code as bch_bio_alloc_pages assumes that it is called on a freshly >> allocate and initialized bio. > > Yes, the offset is modified in bch_bio_alloc_pages(). Where? In my upstream copy of bch_bio_alloc_pages there is no bv_offset manipulation, and I could not see how such a manipulation would make sense. > Normally the bcache > defined block size is 4KB so the issue was not triggered frequently. I > found it during testing my nvdimm enabling code for bcache, where I happen > to make the bcache defined block size to non-4KB. The offset is from the > previous written bkey set, which the minimized unit size is 1 > bcache-defined-block-size. So you have some out of tree changes here? Copying a PAGE_SIZE into a 'segment' bvec just does not make any sense if there is an offset, as segments are defined as bvecs that do not span page boundaries. I suspect the best thing to do in do_btree_node_write would be something like the patch below instead of poking into the internals here, but I'd also really like to understand the root cause as it does point to a bug somewhere else. diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 93b67b8d31c3d..f69914848f32f 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -378,8 +378,8 @@ static void do_btree_node_write(struct btree *b) struct bvec_iter_all iter_all; bio_for_each_segment_all(bv, b->bio, iter_all) { - memcpy(bvec_virt(bv), addr, PAGE_SIZE); - addr += PAGE_SIZE; + memcpy_to_bvec(bvec_virt(bv), addr); + addr += bv->bv_len; } bch_submit_bbio(b->bio, b->c, &k.key, 0);