Re: 5.3-rc1 regression with XFS log recovery

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Wed, 2019-08-21 at 07:44 +1000, Dave Chinner wrote:
> 
> However, the case here is that:
> 
> > > > > i.e. page		offset	len	sector
> > > > > 00000000a77f0146	768	3328	0x7d0048
> > > > > 000000006ceca91e	0	768	0x7d004e
> 
> The second page added to the bvec is actually offset alignedr. Hence
> the check would do nothing on the first page because the bvec array
> is empty (so goes into a new bvec anyway), and the check on the
> second page would do nothing an it would merge with first because
> the offset is aligned correctly. In both cases, the length of the
> segment is not aligned, so that needs to be checked, too.
> 
> IOWs, I think the check needs to be in bio_add_page, it needs to
> check both the offset and length for alignment, and it needs to grab
> the alignment from queue_dma_alignment(), not use a hard coded value
> of 511.
> 
So something like this?

diff --git a/block/bio.c b/block/bio.c
index 299a0e7651ec..80f449d23e5a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -822,8 +822,12 @@ EXPORT_SYMBOL_GPL(__bio_add_page);
 int bio_add_page(struct bio *bio, struct page *page,
                 unsigned int len, unsigned int offset)
 {
+       struct request_queue *q = bio->bi_disk->queue;
        bool same_page = false;
 
+       if (offset & queue_dma_alignment(q) || len & queue_dma_alignment(q))
+               return 0;
+
        if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
                if (bio_full(bio, len))
                        return 0;

I tried this, but the 'mount' just hangs - which looks like it might be
due to xfs_rw_bdev() doing:

  while (bio_add_page(bio, page, len, off) != len) {
  	...