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

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Date:	Thu, 11 Dec 2014 22:32:31 -0800
From:	Ming Lin <mlin@...ggr.net>
To:	Dongsu Park <dongsu.park@...fitbricks.com>
CC:	Kent Overstreet <kmo@...erainc.com>, linux-fsdevel@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: Block layer projects that I haven't had time for

On 12/11/2014 02:07 AM, Dongsu Park wrote:
> 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.)

How about below fix?
"bvec.bv_len != PAGE_CACHE_SIZE" should be not valid any more, because now bio
handles arbitrary size, right?

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 2ac08e2..482c89c 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2468,7 +2468,7 @@ static void end_bio_extent_writepage(struct bio *bio, int err)
 		 * advance bv_offset and adjust bv_len to compensate.
 		 * Print a warning for nonzero offsets, and an error
 		 * if they don't add up to a full page.  */
-		if (bvec.bv_offset || bvec.bv_len != PAGE_CACHE_SIZE) {
+		if (bvec.bv_offset) {
 			if (bvec.bv_offset + bvec.bv_len != PAGE_CACHE_SIZE)
 				btrfs_err(BTRFS_I(page->mapping->host)->root->fs_info,
 				   "partial page write in btrfs with offset %u and length %u",
@@ -2481,7 +2481,7 @@ static void end_bio_extent_writepage(struct bio *bio, int err)
 		}
 
 		start = page_offset(page);
-		end = start + bvec.bv_offset + bvec.bv_len - 1;
+		end = start + bvec.bv_offset + min(bvec.bv_len, PAGE_CACHE_SIZE) - 1;
 
 		if (end_extent_writepage(page, err, start, end))
 			continue;

Thanks,
Ming

> 
> Thanks,
> Dongsu
> 
> ====
> 
> From 7cef37e357b4fd636b3d4aa296e8b67ba8db66d1 Mon Sep 17 00:00:00 2001
> From: Dongsu Park <dongsu.park@...fitbricks.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@...fitbricks.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;
>  
> 
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