On Sat, Apr 06, 2019 at 09:53:07AM +0800, Qu Wenruo wrote:
> Hi,
>
> I'm looking into a strange behavior that we can't break
> bio_for_each_segment_all() after commit 6dc4f100c175 ("block: allow
> bio_for_each_segment_all() to iterate over multi-page bvec").
>
> It's screwing up all bio_for_each_segment_all() call with error out branch.
> bio_for_each_segment_all(bvec, bio, i, iter_all) {
> root = BTRFS_I(bvec->bv_page->mapping->host)->root;
> ret = csum_dirty_buffer(root->fs_info, bvec->bv_page);
> - if (ret)
> + if (ret) {
> + err = ret;
> + pr_info("breaking out with ret=%d\n", ret);
> break;
> + }
> }
>
> + if (err)
> + pr_info("err=%d out, but ret=%d\n",err, ret);
> return errno_to_blk_status(ret);
> }
>
> Straightforward, if we break, we should have err == ret.
>
> Then run fstests btrfs/151, which will trigger a false alert in
> tree-checker:
>
> BTRFS critical (device dm-1): corrupt leaf: root=3 block=570572800
> slot=1 devid=1 invalid total bytes: have 0
> BTRFS error (device dm-1): block=570572800 write time tree block
> corruption detected
> breaking out with ret=-117
> err=-117 out, but ret=0
>
> So it looks like the break line doens't really break, but continue
> executing.
It expands to for-inside-for since that commit, so break only takes you
out of the inner loop...
No comments on desirability of such macros - personally, I prefer to
avoid those, but I'm not stepping into that holy war...
