[PATCH v3 0/9] Fix bio chain related issues

[PATCH v3 0/9] Fix bio chain related issues

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Hi all,

While investigating another problem [mentioned in v1], we identified
some buggy code in the bio chain handling logic. This series addresses
those issues and performs related code cleanup.

Patches 1-3 fix incorrect usage of bio_chain_endio().
Patches 4-9 clean up repetitive code patterns in bio chain handling.

v3:
- Remove the dead code in bio_chain_endio and drop patch 1 in v2 
- Refined the __bio_chain_endio changes with minor modifications (was
  patch 02 in v2).
- Dropped cleanup patches 06 and 12 from v2 due to an incorrect 'prev'
  and 'new' order.

v2:
- Added fix for bcache.
- Added BUG_ON() in bio_chain_endio().
- Enhanced commit messages for each patch
https://lore.kernel.org/all/20251128083219.2332407-1-zhangshida@kylinos.cn/

v1:
https://lore.kernel.org/all/20251121081748.1443507-1-zhangshida@kylinos.cn/

Shida Zhang (9):
  md: bcache: fix improper use of bi_end_io
  block: prohibit calls to bio_chain_endio
  block: prevent race condition on bi_status in __bio_chain_endio
  block: export bio_chain_and_submit
  xfs: Replace the repetitive bio chaining code patterns
  block: Replace the repetitive bio chaining code patterns
  fs/ntfs3: Replace the repetitive bio chaining code patterns
  zram: Replace the repetitive bio chaining code patterns
  nvdimm: Replace the repetitive bio chaining code patterns

 block/bio.c                   | 12 +++++++++---
 drivers/block/zram/zram_drv.c |  3 +--
 drivers/md/bcache/request.c   |  6 +++---
 drivers/nvdimm/nd_virtio.c    |  3 +--
 fs/ntfs3/fsntfs.c             | 12 ++----------
 fs/squashfs/block.c           |  3 +--
 fs/xfs/xfs_bio_io.c           |  3 +--
 fs/xfs/xfs_buf.c              |  3 +--
 fs/xfs/xfs_log.c              |  3 +--
 9 files changed, 20 insertions(+), 28 deletions(-)

-- 
2.34.1

[PATCH v3 1/9] md: bcache: fix improper use of bi_end_io

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Don't call bio->bi_end_io() directly. Use the bio_endio() helper
function instead, which handles completion more safely and uniformly.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 drivers/md/bcache/request.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index af345dc6fde..82fdea7dea7 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -1104,7 +1104,7 @@ static void detached_dev_end_io(struct bio *bio)
 	}
 
 	kfree(ddip);
-	bio->bi_end_io(bio);
+	bio_endio(bio);
 }
 
 static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,
@@ -1121,7 +1121,7 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,
 	ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
 	if (!ddip) {
 		bio->bi_status = BLK_STS_RESOURCE;
-		bio->bi_end_io(bio);
+		bio_endio(bio);
 		return;
 	}
 
@@ -1136,7 +1136,7 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,
 
 	if ((bio_op(bio) == REQ_OP_DISCARD) &&
 	    !bdev_max_discard_sectors(dc->bdev))
-		bio->bi_end_io(bio);
+		detached_dev_end_io(bio);
 	else
 		submit_bio_noacct(bio);
 }
-- 
2.34.1

Re: [PATCH v3 1/9] md: bcache: fix improper use of bi_end_io

[Coly Li]

> 2025年11月29日 17:01，zhangshida <starzhangzsd@gmail.com> 写道：
> 
> From: Shida Zhang <zhangshida@kylinos.cn>
> 
> Don't call bio->bi_end_io() directly. Use the bio_endio() helper
> function instead, which handles completion more safely and uniformly.
> 
> Suggested-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
> ---
> drivers/md/bcache/request.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index af345dc6fde..82fdea7dea7 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c

[snipped]

The patch is good. Please modify the patch subject to:  bcache: fix improper use of bi_end_io

You may directly send the refined version to linux-bcache mailing list, I will take it.

Thanks.

Coly Li

Re: [PATCH v3 1/9] md: bcache: fix improper use of bi_end_io

[Stephen Zhang]

Coly Li <colyli@fnnas.com> 于2025年12月1日周一 13:45写道：
>
> > 2025年11月29日 17:01，zhangshida <starzhangzsd@gmail.com> 写道：
> >
> > From: Shida Zhang <zhangshida@kylinos.cn>
> >
> > Don't call bio->bi_end_io() directly. Use the bio_endio() helper
> > function instead, which handles completion more safely and uniformly.
> >
> > Suggested-by: Christoph Hellwig <hch@infradead.org>
> > Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
> > ---
> > drivers/md/bcache/request.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> > index af345dc6fde..82fdea7dea7 100644
> > --- a/drivers/md/bcache/request.c
> > +++ b/drivers/md/bcache/request.c
>
> [snipped]
>
> The patch is good. Please modify the patch subject to:  bcache: fix improper use of bi_end_io
>
> You may directly send the refined version to linux-bcache mailing list, I will take it.
>

Thank you. This has now been taken care of.

Thanks,
Shida

> Thanks.
>
> Coly Li

[PATCH v3 2/9] block: prohibit calls to bio_chain_endio

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Now that all potential callers of bio_chain_endio have been
eliminated, completely prohibit any future calls to this function.

Suggested-by: Ming Lei <ming.lei@redhat.com>
Suggested-by: Andreas Gruenbacher <agruenba@redhat.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 block/bio.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index b3a79285c27..1b5e4577f4c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -320,9 +320,13 @@ static struct bio *__bio_chain_endio(struct bio *bio)
 	return parent;
 }
 
+/**
+ * This function should only be used as a flag and must never be called.
+ * If execution reaches here, it indicates a serious programming error.
+ */
 static void bio_chain_endio(struct bio *bio)
 {
-	bio_endio(__bio_chain_endio(bio));
+	BUG_ON(1);
 }
 
 /**
-- 
2.34.1

Re: [PATCH v3 2/9] block: prohibit calls to bio_chain_endio

[Christoph Hellwig]

On Sat, Nov 29, 2025 at 05:01:15PM +0800, zhangshida wrote:
> From: Shida Zhang <zhangshida@kylinos.cn>
> 
> Now that all potential callers of bio_chain_endio have been
> eliminated, completely prohibit any future calls to this function.

Note that we'll need to be prepared for a flame from Linus for
using BUG_ON, but I still think it is reasonable here.

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH v3 3/9] block: prevent race condition on bi_status in __bio_chain_endio

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Andreas point out that multiple completions can race setting
bi_status.

The check (parent->bi_status) and the subsequent write are not an
atomic operation. The value of parent->bi_status could have changed
between the time you read it for the if check and the time you write
to it. So we use cmpxchg to fix the race, as suggested by Christoph.

Suggested-by: Andreas Gruenbacher <agruenba@redhat.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 block/bio.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 1b5e4577f4c..097c1cd2054 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -314,8 +314,9 @@ static struct bio *__bio_chain_endio(struct bio *bio)
 {
 	struct bio *parent = bio->bi_private;
 
-	if (bio->bi_status && !parent->bi_status)
-		parent->bi_status = bio->bi_status;
+	if (bio->bi_status)
+		cmpxchg(&parent->bi_status, 0, bio->bi_status);
+
 	bio_put(bio);
 	return parent;
 }
-- 
2.34.1

Re: [PATCH v3 3/9] block: prevent race condition on bi_status in __bio_chain_endio

[Christoph Hellwig]

On Sat, Nov 29, 2025 at 05:01:16PM +0800, zhangshida wrote:
> From: Shida Zhang <zhangshida@kylinos.cn>
> 
> Andreas point out that multiple completions can race setting
> bi_status.
> 
> The check (parent->bi_status) and the subsequent write are not an
> atomic operation. The value of parent->bi_status could have changed
> between the time you read it for the if check and the time you write
> to it. So we use cmpxchg to fix the race, as suggested by Christoph.

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v3 3/9] block: prevent race condition on bi_status in __bio_chain_endio

[kernel test robot]

Hi zhangshida,

kernel test robot noticed the following build warnings:

[auto build test WARNING on axboe/for-next]
[also build test WARNING on xfs-linux/for-next nvdimm/libnvdimm-for-next linus/master brauner-vfs/vfs.all v6.18 next-20251205]
[cannot apply to nvdimm/dax-misc]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/zhangshida/md-bcache-fix-improper-use-of-bi_end_io/20251129-170348
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
patch link:    https://lore.kernel.org/r/20251129090122.2457896-4-zhangshida%40kylinos.cn
patch subject: [PATCH v3 3/9] block: prevent race condition on bi_status in __bio_chain_endio
config: loongarch-randconfig-r133-20251130 (https://download.01.org/0day-ci/archive/20251207/202512070122.my7vkR7A-lkp@intel.com/config)
compiler: loongarch64-linux-gcc (GCC) 14.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251207/202512070122.my7vkR7A-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512070122.my7vkR7A-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> block/bio.c:319:17: sparse: sparse: cast from restricted blk_status_t
>> block/bio.c:319:17: sparse: sparse: cast from restricted blk_status_t
>> block/bio.c:319:17: sparse: sparse: cast to restricted blk_status_t

vim +319 block/bio.c

   313	
   314	static struct bio *__bio_chain_endio(struct bio *bio)
   315	{
   316		struct bio *parent = bio->bi_private;
   317	
   318		if (bio->bi_status)
 > 319			cmpxchg(&parent->bi_status, 0, bio->bi_status);
   320	
   321		bio_put(bio);
   322		return parent;
   323	}
   324	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

[PATCH v3 4/9] block: export bio_chain_and_submit

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Export the bio_chain_and_submit function to make it available as a
common utility. This will allow replacing repetitive bio chaining
patterns found in multiple locations throughout the codebase.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 block/bio.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/bio.c b/block/bio.c
index 097c1cd2054..7aa4a1d3672 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -368,6 +368,7 @@ struct bio *bio_chain_and_submit(struct bio *prev, struct bio *new)
 	}
 	return new;
 }
+EXPORT_SYMBOL_GPL(bio_chain_and_submit);
 
 struct bio *blk_next_bio(struct bio *bio, struct block_device *bdev,
 		unsigned int nr_pages, blk_opf_t opf, gfp_t gfp)
-- 
2.34.1

Re: [PATCH v3 4/9] block: export bio_chain_and_submit

[Christoph Hellwig]

Please split this and the remainder into a separate series, to be
resubmitted after -rc1.

[PATCH v3 5/9] xfs: Replace the repetitive bio chaining code patterns

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Replace duplicate bio chaining logic with the common
bio_chain_and_submit helper function.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 fs/xfs/xfs_bio_io.c | 3 +--
 fs/xfs/xfs_buf.c    | 3 +--
 fs/xfs/xfs_log.c    | 3 +--
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_bio_io.c b/fs/xfs/xfs_bio_io.c
index 2a736d10eaf..4a6577b0789 100644
--- a/fs/xfs/xfs_bio_io.c
+++ b/fs/xfs/xfs_bio_io.c
@@ -38,8 +38,7 @@ xfs_rw_bdev(
 					bio_max_vecs(count - done),
 					prev->bi_opf, GFP_KERNEL);
 			bio->bi_iter.bi_sector = bio_end_sector(prev);
-			bio_chain(prev, bio);
-			submit_bio(prev);
+			bio_chain_and_submit(prev, bio);
 		}
 		done += added;
 	} while (done < count);
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 773d959965d..c26bd28edb4 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1357,8 +1357,7 @@ xfs_buf_submit_bio(
 		split = bio_split(bio, bp->b_maps[map].bm_len, GFP_NOFS,
 				&fs_bio_set);
 		split->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
-		bio_chain(split, bio);
-		submit_bio(split);
+		bio_chain_and_submit(split, bio);
 	}
 	bio->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
 	submit_bio(bio);
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 603e85c1ab4..f4c9ad1d148 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1687,8 +1687,7 @@ xlog_write_iclog(
 
 		split = bio_split(&iclog->ic_bio, log->l_logBBsize - bno,
 				  GFP_NOIO, &fs_bio_set);
-		bio_chain(split, &iclog->ic_bio);
-		submit_bio(split);
+		bio_chain_and_submit(split, &iclog->ic_bio);
 
 		/* restart at logical offset zero for the remainder */
 		iclog->ic_bio.bi_iter.bi_sector = log->l_logBBstart;
-- 
2.34.1

[PATCH v3 6/9] block: Replace the repetitive bio chaining code patterns

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Replace duplicate bio chaining logic with the common
bio_chain_and_submit helper function.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 fs/squashfs/block.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
index a05e3793f93..5818e473255 100644
--- a/fs/squashfs/block.c
+++ b/fs/squashfs/block.c
@@ -126,8 +126,7 @@ static int squashfs_bio_read_cached(struct bio *fullbio,
 			if (bio) {
 				bio_trim(bio, start_idx * PAGE_SECTORS,
 					 (end_idx - start_idx) * PAGE_SECTORS);
-				bio_chain(bio, new);
-				submit_bio(bio);
+				bio_chain_and_submit(bio, new);
 			}
 
 			bio = new;
-- 
2.34.1

[PATCH v3 7/9] fs/ntfs3: Replace the repetitive bio chaining code patterns

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Replace duplicate bio chaining logic with the common
bio_chain_and_submit helper function.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 fs/ntfs3/fsntfs.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/fs/ntfs3/fsntfs.c b/fs/ntfs3/fsntfs.c
index c7a2f191254..35685ee4ed2 100644
--- a/fs/ntfs3/fsntfs.c
+++ b/fs/ntfs3/fsntfs.c
@@ -1514,11 +1514,7 @@ int ntfs_bio_pages(struct ntfs_sb_info *sbi, const struct runs_tree *run,
 		len = ((u64)clen << cluster_bits) - off;
 new_bio:
 		new = bio_alloc(bdev, nr_pages - page_idx, op, GFP_NOFS);
-		if (bio) {
-			bio_chain(bio, new);
-			submit_bio(bio);
-		}
-		bio = new;
+		bio = bio_chain_and_submit(bio, new);
 		bio->bi_iter.bi_sector = lbo >> 9;
 
 		while (len) {
@@ -1611,11 +1607,7 @@ int ntfs_bio_fill_1(struct ntfs_sb_info *sbi, const struct runs_tree *run)
 		len = (u64)clen << cluster_bits;
 new_bio:
 		new = bio_alloc(bdev, BIO_MAX_VECS, REQ_OP_WRITE, GFP_NOFS);
-		if (bio) {
-			bio_chain(bio, new);
-			submit_bio(bio);
-		}
-		bio = new;
+		bio = bio_chain_and_submit(bio, new);
 		bio->bi_iter.bi_sector = lbo >> 9;
 
 		for (;;) {
-- 
2.34.1

[PATCH v3 8/9] zram: Replace the repetitive bio chaining code patterns

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Replace duplicate bio chaining logic with the common
bio_chain_and_submit helper function.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 drivers/block/zram/zram_drv.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a4307465753..084de60ebaf 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -730,8 +730,7 @@ static void read_from_bdev_async(struct zram *zram, struct page *page,
 	bio = bio_alloc(zram->bdev, 1, parent->bi_opf, GFP_NOIO);
 	bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
 	__bio_add_page(bio, page, PAGE_SIZE, 0);
-	bio_chain(bio, parent);
-	submit_bio(bio);
+	bio_chain_and_submit(bio, parent);
 }
 
 static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl)
-- 
2.34.1

Re: [PATCH v3 8/9] zram: Replace the repetitive bio chaining code patterns

[Sergey Senozhatsky]

On (25/11/29 17:01), zhangshida wrote:
> Replace duplicate bio chaining logic with the common
> bio_chain_and_submit helper function.

A friendly hint: Cc-ing maintainers doesn't hurt, mostly.

Looks good to me, there is a slight chance of a conflict with
another pending zram patches, but it's quite trivial to resolve.

Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>

[PATCH v3 9/9] nvdimm: Replace the repetitive bio chaining code patterns

[zhangshida]

From: Shida Zhang <zhangshida@kylinos.cn>

Replace duplicate bio chaining logic with the common
bio_chain_and_submit helper function.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 drivers/nvdimm/nd_virtio.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
index c3f07be4aa2..e6ec7ceee9b 100644
--- a/drivers/nvdimm/nd_virtio.c
+++ b/drivers/nvdimm/nd_virtio.c
@@ -122,8 +122,7 @@ int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
 			return -ENOMEM;
 		bio_clone_blkg_association(child, bio);
 		child->bi_iter.bi_sector = -1;
-		bio_chain(child, bio);
-		submit_bio(child);
+		bio_chain_and_submit(child, bio);
 		return 0;
 	}
 	if (virtio_pmem_flush(nd_region))
-- 
2.34.1