[V3] block: don't use for-inside-for in bio_for_each_segment_all
diff mbox series

Message ID 20190408110238.30478-1-ming.lei@redhat.com
State New
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Series
  • [V3] block: don't use for-inside-for in bio_for_each_segment_all
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Commit Message

Ming Lei April 8, 2019, 11:02 a.m. UTC
Commit 6dc4f100c175 ("block: allow bio_for_each_segment_all() to
iterate over multi-page bvec") changes bio_for_each_segment_all()
to use for-inside-for.

This way breaks all bio_for_each_segment_all() call with error out
branch via 'break', since now 'break' can only break from the inner
loop.

Fixes this issue by implementing bio_for_each_segment_all() via
single 'for' loop, and now the logic is very similar with normal
bvec iterator.

Cc: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: linux-btrfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: Omar Sandoval <osandov@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Reported-and-Tested-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
Fixes: 6dc4f100c175 ("block: allow bio_for_each_segment_all() to iterate over multi-page bvec")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
V3:
	- don't rename for avoiding conflict with hch's patches
V2:
	- address comments: avoid explicated expressiones in macro, naming


 include/linux/bio.h  | 20 ++++++++++++--------
 include/linux/bvec.h | 14 ++++++++++----
 2 files changed, 22 insertions(+), 12 deletions(-)

Comments

Johannes Thumshirn April 8, 2019, 11:20 a.m. UTC | #1
Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Jens Axboe April 8, 2019, 2:19 p.m. UTC | #2
On 4/8/19 5:02 AM, Ming Lei wrote:
> Commit 6dc4f100c175 ("block: allow bio_for_each_segment_all() to
> iterate over multi-page bvec") changes bio_for_each_segment_all()
> to use for-inside-for.
> 
> This way breaks all bio_for_each_segment_all() call with error out
> branch via 'break', since now 'break' can only break from the inner
> loop.
> 
> Fixes this issue by implementing bio_for_each_segment_all() via
> single 'for' loop, and now the logic is very similar with normal
> bvec iterator.

Applied, thanks Ming.
David Sterba April 11, 2019, 1:26 p.m. UTC | #3
On Mon, Apr 08, 2019 at 08:19:59AM -0600, Jens Axboe wrote:
> On 4/8/19 5:02 AM, Ming Lei wrote:
> > Commit 6dc4f100c175 ("block: allow bio_for_each_segment_all() to
> > iterate over multi-page bvec") changes bio_for_each_segment_all()
> > to use for-inside-for.
> > 
> > This way breaks all bio_for_each_segment_all() call with error out
> > branch via 'break', since now 'break' can only break from the inner
> > loop.
> > 
> > Fixes this issue by implementing bio_for_each_segment_all() via
> > single 'for' loop, and now the logic is very similar with normal
> > bvec iterator.
> 
> Applied, thanks Ming.

What's the merge target please? This affects btrfs testing so I wonder
if we should start adding workarounds or just wait for the next rc.
Thanks.
Jens Axboe April 11, 2019, 3:07 p.m. UTC | #4
On 4/11/19 7:26 AM, David Sterba wrote:
> On Mon, Apr 08, 2019 at 08:19:59AM -0600, Jens Axboe wrote:
>> On 4/8/19 5:02 AM, Ming Lei wrote:
>>> Commit 6dc4f100c175 ("block: allow bio_for_each_segment_all() to
>>> iterate over multi-page bvec") changes bio_for_each_segment_all()
>>> to use for-inside-for.
>>>
>>> This way breaks all bio_for_each_segment_all() call with error out
>>> branch via 'break', since now 'break' can only break from the inner
>>> loop.
>>>
>>> Fixes this issue by implementing bio_for_each_segment_all() via
>>> single 'for' loop, and now the logic is very similar with normal
>>> bvec iterator.
>>
>> Applied, thanks Ming.
> 
> What's the merge target please? This affects btrfs testing so I wonder
> if we should start adding workarounds or just wait for the next rc.
> Thanks.

It's queued up in my for-linus, so it's for this series. It'll go
upstream tomorrow.

Patch
diff mbox series

diff --git a/include/linux/bio.h b/include/linux/bio.h
index bb6090aa165d..e584673c1881 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -120,19 +120,23 @@  static inline bool bio_full(struct bio *bio)
 	return bio->bi_vcnt >= bio->bi_max_vecs;
 }
 
-#define mp_bvec_for_each_segment(bv, bvl, i, iter_all)			\
-	for (bv = bvec_init_iter_all(&iter_all);			\
-		(iter_all.done < (bvl)->bv_len) &&			\
-		(mp_bvec_next_segment((bvl), &iter_all), 1);		\
-		iter_all.done += bv->bv_len, i += 1)
+static inline bool bio_next_segment(const struct bio *bio,
+				    struct bvec_iter_all *iter)
+{
+	if (iter->idx >= bio->bi_vcnt)
+		return false;
+
+	bvec_advance(&bio->bi_io_vec[iter->idx], iter);
+	return true;
+}
 
 /*
  * drivers should _never_ use the all version - the bio may have been split
  * before it got to the driver and the driver won't own all of it
  */
-#define bio_for_each_segment_all(bvl, bio, i, iter_all)		\
-	for (i = 0, iter_all.idx = 0; iter_all.idx < (bio)->bi_vcnt; iter_all.idx++)	\
-		mp_bvec_for_each_segment(bvl, &((bio)->bi_io_vec[iter_all.idx]), i, iter_all)
+#define bio_for_each_segment_all(bvl, bio, i, iter)			\
+	for (i = 0, bvl = bvec_init_iter_all(&iter);			\
+	     bio_next_segment((bio), &iter); i++)
 
 static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 				    unsigned bytes)
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index f6275c4da13a..3bc91879e1e2 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -145,18 +145,18 @@  static inline bool bvec_iter_advance(const struct bio_vec *bv,
 
 static inline struct bio_vec *bvec_init_iter_all(struct bvec_iter_all *iter_all)
 {
-	iter_all->bv.bv_page = NULL;
 	iter_all->done = 0;
+	iter_all->idx = 0;
 
 	return &iter_all->bv;
 }
 
-static inline void mp_bvec_next_segment(const struct bio_vec *bvec,
-					struct bvec_iter_all *iter_all)
+static inline void bvec_advance(const struct bio_vec *bvec,
+				struct bvec_iter_all *iter_all)
 {
 	struct bio_vec *bv = &iter_all->bv;
 
-	if (bv->bv_page) {
+	if (iter_all->done) {
 		bv->bv_page = nth_page(bv->bv_page, 1);
 		bv->bv_offset = 0;
 	} else {
@@ -165,6 +165,12 @@  static inline void mp_bvec_next_segment(const struct bio_vec *bvec,
 	}
 	bv->bv_len = min_t(unsigned int, PAGE_SIZE - bv->bv_offset,
 			   bvec->bv_len - iter_all->done);
+	iter_all->done += bv->bv_len;
+
+	if (iter_all->done == bvec->bv_len) {
+		iter_all->idx++;
+		iter_all->done = 0;
+	}
 }
 
 /*