Re: Block layer projects that I haven't had time for

[Dongsu Park <dongsu.park@profitbricks.com>]

Hi Ming & Kent,

On 10.12.2014 23:11, Ming Lin wrote:
> > On Wed, Dec 10, 2014 at 02:42:14PM -0800, Ming Lin wrote:
> > Try this fix:
> Yes, it fixed ext4 problem.

@kent: Thank you for the patch. Indeed it fixes the ext4 lockup I've seen.
I've applied it to my tree, under the branch block-mpage-bvecs-for-next.
See 0d2e05525a58 ("fs/ext4: fix a lockup when writing blocks into ext4
rootfs") <https://github.com/dongsupark/linux/commit/0d2e05525a58>.

After that of course, more bugs start to appear, e.g. crash with virtio-blk,
like we'd have opened a can of worms. ;-)

> Just tried to edit a btrfs file.
> 
> [   45.216351] BTRFS error (device sdb1): partial page write in btrfs with
> offset 0 and length 8192
> [   45.217522] BTRFS critical (device sdb1): bad ordered accounting left 0
> size 4096

@ming: I guess you managed to see this error as you're testing with a
SCSI device, not virtio-blk device like me.
Are you seeing it without any back traces?
Does the attached patch fix your issue?
(This is already included in the branch block-mpage-bvecs-for-next.)

Thanks,
Dongsu

====

>From 7cef37e357b4fd636b3d4aa296e8b67ba8db66d1 Mon Sep 17 00:00:00 2001
From: Dongsu Park <dongsu.park@profitbricks.com>
Date: Tue, 9 Dec 2014 18:10:10 +0100
Subject: [PATCH] btrfs: use a correct function for bvec iteration in
 btrfs_csum_one_bio()

Commit 94607a8a("block: Convert various code to bio_for_each_page()")
introduced a critical bug in btrfs_csum_one_bio() using
bio_for_each_page_all() for iterating through each bvec.
That should actually call bio_for_each_page() to take the current
offset into account. Without this fix, xfstests/btrfs/012 would
end up with lockup with warnings in btrfs_add_ordered_sum(), because
iter.bi_size becomes < 0.

Signed-off-by: Dongsu Park <dongsu.park@profitbricks.com>
---
 fs/btrfs/file-item.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 6a81176..c7ae23c 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -447,7 +447,7 @@ int btrfs_csum_one_bio(struct btrfs_root *root, struct inode *inode,
 	sums->bytenr = (u64)bio->bi_iter.bi_sector << 9;
 	index = 0;
 
-	bio_for_each_page_all(bvec, bio, iter) {
+	bio_for_each_page(bvec, bio, iter) {
 		if (!contig)
 			offset = page_offset(bvec.bv_page) + bvec.bv_offset;
 
-- 
1.9.3