zram I/O path cleanups and fixups

zram I/O path cleanups and fixups

[Christoph Hellwig]

Hi all,

this series cleans up the zram I/O path, and fixes the handling of
synchronous I/O to the underlying device in the writeback_store
function or for > 4K PAGE_SIZE systems.

The fixes are at the end, as I could not fully reason about them being
safe before untangling the callchain.

This survives xfstests on two zram devices on x86, but I don't actually
have a large PAGE_SIZE system to test that path on.

Diffstat:
 zram_drv.c |  375 ++++++++++++++++++++++---------------------------------------
 zram_drv.h |    1 
 2 files changed, 136 insertions(+), 240 deletions(-)

[PATCH 01/16] zram: remove valid_io_request

[Christoph Hellwig]

All bios hande to drivers from the block layer are checked against the
device size and for logical block alignment already, so don't duplicate
those checks.  Merge __zram_make_request into zram_submit_bio now that
there is no point in splitting them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 34 +---------------------------------
 drivers/block/zram/zram_drv.h |  1 -
 2 files changed, 1 insertion(+), 34 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index aa490da3cef233..0c6b3ba2970b5f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -174,30 +174,6 @@ static inline u32 zram_get_priority(struct zram *zram, u32 index)
 	return prio & ZRAM_COMP_PRIORITY_MASK;
 }
 
-/*
- * Check if request is within bounds and aligned on zram logical blocks.
- */
-static inline bool valid_io_request(struct zram *zram,
-		sector_t start, unsigned int size)
-{
-	u64 end, bound;
-
-	/* unaligned request */
-	if (unlikely(start & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
-		return false;
-	if (unlikely(size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
-		return false;
-
-	end = start + (size >> SECTOR_SHIFT);
-	bound = zram->disksize >> SECTOR_SHIFT;
-	/* out of range */
-	if (unlikely(start >= bound || end > bound || start > end))
-		return false;
-
-	/* I/O request is valid */
-	return true;
-}
-
 static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
 {
 	*index  += (*offset + bvec->bv_len) / PAGE_SIZE;
@@ -1190,10 +1166,9 @@ static ssize_t io_stat_show(struct device *dev,
 
 	down_read(&zram->init_lock);
 	ret = scnprintf(buf, PAGE_SIZE,
-			"%8llu %8llu %8llu %8llu\n",
+			"%8llu %8llu 0 %8llu\n",
 			(u64)atomic64_read(&zram->stats.failed_reads),
 			(u64)atomic64_read(&zram->stats.failed_writes),
-			(u64)atomic64_read(&zram->stats.invalid_io),
 			(u64)atomic64_read(&zram->stats.notify_free));
 	up_read(&zram->init_lock);
 
@@ -2043,13 +2018,6 @@ static void zram_submit_bio(struct bio *bio)
 {
 	struct zram *zram = bio->bi_bdev->bd_disk->private_data;
 
-	if (!valid_io_request(zram, bio->bi_iter.bi_sector,
-					bio->bi_iter.bi_size)) {
-		atomic64_inc(&zram->stats.invalid_io);
-		bio_io_error(bio);
-		return;
-	}
-
 	__zram_make_request(zram, bio);
 }
 
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index c5254626f051fa..ca7a15bd48456a 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -78,7 +78,6 @@ struct zram_stats {
 	atomic64_t compr_data_size;	/* compressed size of pages stored */
 	atomic64_t failed_reads;	/* can happen when memory is too low */
 	atomic64_t failed_writes;	/* can happen when memory is too low */
-	atomic64_t invalid_io;	/* non-page-aligned I/O requests */
 	atomic64_t notify_free;	/* no. of swap slot free notifications */
 	atomic64_t same_pages;		/* no. of same element filled pages */
 	atomic64_t huge_pages;		/* no. of huge pages */
-- 
2.39.2

[PATCH 02/16] zram: make zram_bio_discard more self-contained

[Christoph Hellwig]

Derive the index and offset variables inside the function, and complete
the bio directly in preparation for cleaning up the I/O path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0c6b3ba2970b5f..3d8e2a1db7c7d3 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1896,15 +1896,12 @@ static ssize_t recompress_store(struct device *dev,
 }
 #endif
 
-/*
- * zram_bio_discard - handler on discard request
- * @index: physical block index in PAGE_SIZE units
- * @offset: byte offset within physical block
- */
-static void zram_bio_discard(struct zram *zram, u32 index,
-			     int offset, struct bio *bio)
+static void zram_bio_discard(struct zram *zram, struct bio *bio)
 {
 	size_t n = bio->bi_iter.bi_size;
+	u32 index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+	u32 offset = (bio->bi_iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+			SECTOR_SHIFT;
 
 	/*
 	 * zram manages data in physical block size units. Because logical block
@@ -1932,6 +1929,8 @@ static void zram_bio_discard(struct zram *zram, u32 index,
 		index++;
 		n -= PAGE_SIZE;
 	}
+
+	bio_endio(bio);
 }
 
 /*
@@ -1980,8 +1979,7 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
 	case REQ_OP_WRITE_ZEROES:
-		zram_bio_discard(zram, index, offset, bio);
-		bio_endio(bio);
+		zram_bio_discard(zram, bio);
 		return;
 	default:
 		break;
-- 
2.39.2

[PATCH 03/16] zram: implify bvec iteration in __zram_make_request

[Christoph Hellwig]

bio_for_each_segment synthetize bvecs that never cross page boundaries,
so don't duplicate that work in an inner loop.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 42 +++++++++--------------------------
 1 file changed, 11 insertions(+), 31 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3d8e2a1db7c7d3..5f1e4fd23ade32 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -174,12 +174,6 @@ static inline u32 zram_get_priority(struct zram *zram, u32 index)
 	return prio & ZRAM_COMP_PRIORITY_MASK;
 }
 
-static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
-{
-	*index  += (*offset + bvec->bv_len) / PAGE_SIZE;
-	*offset = (*offset + bvec->bv_len) % PAGE_SIZE;
-}
-
 static inline void update_used_max(struct zram *zram,
 					const unsigned long pages)
 {
@@ -1966,16 +1960,10 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 static void __zram_make_request(struct zram *zram, struct bio *bio)
 {
-	int offset;
-	u32 index;
-	struct bio_vec bvec;
 	struct bvec_iter iter;
+	struct bio_vec bv;
 	unsigned long start_time;
 
-	index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
-	offset = (bio->bi_iter.bi_sector &
-		  (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
-
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
 	case REQ_OP_WRITE_ZEROES:
@@ -1986,24 +1974,16 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 	}
 
 	start_time = bio_start_io_acct(bio);
-	bio_for_each_segment(bvec, bio, iter) {
-		struct bio_vec bv = bvec;
-		unsigned int unwritten = bvec.bv_len;
-
-		do {
-			bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
-							unwritten);
-			if (zram_bvec_rw(zram, &bv, index, offset,
-					 bio_op(bio), bio) < 0) {
-				bio->bi_status = BLK_STS_IOERR;
-				break;
-			}
-
-			bv.bv_offset += bv.bv_len;
-			unwritten -= bv.bv_len;
-
-			update_position(&index, &offset, &bv);
-		} while (unwritten);
+	bio_for_each_segment(bv, bio, iter) {
+		u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+				SECTOR_SHIFT;
+
+		if (zram_bvec_rw(zram, &bv, index, offset, bio_op(bio),
+				bio) < 0) {
+			bio->bi_status = BLK_STS_IOERR;
+			break;
+		}
 	}
 	bio_end_io_acct(bio, start_time);
 	bio_endio(bio);
-- 
2.39.2

[PATCH 04/16] zram: move discard handling to zram_submit_bio

[Christoph Hellwig]

Switch on the bio operation in zram_submit_bio and only call into
__zram_make_request for read and write operations.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 5f1e4fd23ade32..6522b888839cb1 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1964,15 +1964,6 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 	struct bio_vec bv;
 	unsigned long start_time;
 
-	switch (bio_op(bio)) {
-	case REQ_OP_DISCARD:
-	case REQ_OP_WRITE_ZEROES:
-		zram_bio_discard(zram, bio);
-		return;
-	default:
-		break;
-	}
-
 	start_time = bio_start_io_acct(bio);
 	bio_for_each_segment(bv, bio, iter) {
 		u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
@@ -1996,7 +1987,19 @@ static void zram_submit_bio(struct bio *bio)
 {
 	struct zram *zram = bio->bi_bdev->bd_disk->private_data;
 
-	__zram_make_request(zram, bio);
+	switch (bio_op(bio)) {
+	case REQ_OP_READ:
+	case REQ_OP_WRITE:
+		__zram_make_request(zram, bio);
+		break;
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		zram_bio_discard(zram, bio);
+		return;
+	default:
+		WARN_ON_ONCE(1);
+		bio_endio(bio);
+	}
 }
 
 static void zram_slot_free_notify(struct block_device *bdev,
-- 
2.39.2

[PATCH 05/16] zram: return early on error in zram_bvec_rw

[Christoph Hellwig]

When the low-level access fails, don't clear the idle flag or clear
the caches, and just return.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 6522b888839cb1..6196187e9ac36f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1939,23 +1939,23 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 
 	if (!op_is_write(op)) {
 		ret = zram_bvec_read(zram, bvec, index, offset, bio);
+		if (unlikely(ret < 0)) {
+			atomic64_inc(&zram->stats.failed_writes);
+			return ret;
+		}
 		flush_dcache_page(bvec->bv_page);
 	} else {
 		ret = zram_bvec_write(zram, bvec, index, offset, bio);
+		if (unlikely(ret < 0)) {
+			atomic64_inc(&zram->stats.failed_reads);
+			return ret;
+		}
 	}
 
 	zram_slot_lock(zram, index);
 	zram_accessed(zram, index);
 	zram_slot_unlock(zram, index);
-
-	if (unlikely(ret < 0)) {
-		if (!op_is_write(op))
-			atomic64_inc(&zram->stats.failed_reads);
-		else
-			atomic64_inc(&zram->stats.failed_writes);
-	}
-
-	return ret;
+	return 0;
 }
 
 static void __zram_make_request(struct zram *zram, struct bio *bio)
-- 
2.39.2

[PATCH 06/16] zram: refactor highlevel read and write handling

[Christoph Hellwig]

Instead of having an outer loop in __zram_make_request and then branch
out for reads vs writes for each loop iteration in zram_bvec_rw, split
the main handler into separat zram_bio_read and zram_bio_write handlers
that also include the functionality formerly in zram_bvec_rw.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 58 ++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 28 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 6196187e9ac36f..83991cb61edaf6 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1927,38 +1927,34 @@ static void zram_bio_discard(struct zram *zram, struct bio *bio)
 	bio_endio(bio);
 }
 
-/*
- * Returns errno if it has some problem. Otherwise return 0 or 1.
- * Returns 0 if IO request was done synchronously
- * Returns 1 if IO request was successfully submitted.
- */
-static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
-			int offset, enum req_op op, struct bio *bio)
+static void zram_bio_read(struct zram *zram, struct bio *bio)
 {
-	int ret;
+	struct bvec_iter iter;
+	struct bio_vec bv;
+	unsigned long start_time;
 
-	if (!op_is_write(op)) {
-		ret = zram_bvec_read(zram, bvec, index, offset, bio);
-		if (unlikely(ret < 0)) {
+	start_time = bio_start_io_acct(bio);
+	bio_for_each_segment(bv, bio, iter) {
+		u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+				SECTOR_SHIFT;
+
+		if (zram_bvec_read(zram, &bv, index, offset, bio) < 0) {
 			atomic64_inc(&zram->stats.failed_writes);
-			return ret;
-		}
-		flush_dcache_page(bvec->bv_page);
-	} else {
-		ret = zram_bvec_write(zram, bvec, index, offset, bio);
-		if (unlikely(ret < 0)) {
-			atomic64_inc(&zram->stats.failed_reads);
-			return ret;
+			bio->bi_status = BLK_STS_IOERR;
+			break;
 		}
-	}
+		flush_dcache_page(bv.bv_page);
 
-	zram_slot_lock(zram, index);
-	zram_accessed(zram, index);
-	zram_slot_unlock(zram, index);
-	return 0;
+		zram_slot_lock(zram, index);
+		zram_accessed(zram, index);
+		zram_slot_unlock(zram, index);
+	}
+	bio_end_io_acct(bio, start_time);
+	bio_endio(bio);
 }
 
-static void __zram_make_request(struct zram *zram, struct bio *bio)
+static void zram_bio_write(struct zram *zram, struct bio *bio)
 {
 	struct bvec_iter iter;
 	struct bio_vec bv;
@@ -1970,11 +1966,15 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
 				SECTOR_SHIFT;
 
-		if (zram_bvec_rw(zram, &bv, index, offset, bio_op(bio),
-				bio) < 0) {
+		if (zram_bvec_write(zram, &bv, index, offset, bio) < 0) {
+			atomic64_inc(&zram->stats.failed_reads);
 			bio->bi_status = BLK_STS_IOERR;
 			break;
 		}
+
+		zram_slot_lock(zram, index);
+		zram_accessed(zram, index);
+		zram_slot_unlock(zram, index);
 	}
 	bio_end_io_acct(bio, start_time);
 	bio_endio(bio);
@@ -1989,8 +1989,10 @@ static void zram_submit_bio(struct bio *bio)
 
 	switch (bio_op(bio)) {
 	case REQ_OP_READ:
+		zram_bio_read(zram, bio);
+		break;
 	case REQ_OP_WRITE:
-		__zram_make_request(zram, bio);
+		zram_bio_write(zram, bio);
 		break;
 	case REQ_OP_DISCARD:
 	case REQ_OP_WRITE_ZEROES:
-- 
2.39.2

[PATCH 07/16] zram: don't use highmem for the bounce buffer in zram_bvec_{read,write}

[Christoph Hellwig]

There is no point in allocation a highmem page when we instantly need
to copy from it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 83991cb61edaf6..0e91e94f24cd09 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1437,7 +1437,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	page = bvec->bv_page;
 	if (is_partial_io(bvec)) {
 		/* Use a temporary buffer to decompress the page */
-		page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
+		page = alloc_page(GFP_NOIO);
 		if (!page)
 			return -ENOMEM;
 	}
@@ -1446,12 +1446,8 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	if (unlikely(ret))
 		goto out;
 
-	if (is_partial_io(bvec)) {
-		void *src = kmap_atomic(page);
-
-		memcpy_to_bvec(bvec, src + offset);
-		kunmap_atomic(src);
-	}
+	if (is_partial_io(bvec))
+		memcpy_to_bvec(bvec, page_address(page) + offset);
 out:
 	if (is_partial_io(bvec))
 		__free_page(page);
@@ -1595,12 +1591,11 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 
 	vec = *bvec;
 	if (is_partial_io(bvec)) {
-		void *dst;
 		/*
 		 * This is a partial IO. We need to read the full page
 		 * before to write the changes.
 		 */
-		page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
+		page = alloc_page(GFP_NOIO);
 		if (!page)
 			return -ENOMEM;
 
@@ -1608,9 +1603,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 		if (ret)
 			goto out;
 
-		dst = kmap_atomic(page);
-		memcpy_from_bvec(dst + offset, bvec);
-		kunmap_atomic(dst);
+		memcpy_from_bvec(page_address(page) + offset, bvec);
 
 		bvec_set_page(&vec, page, PAGE_SIZE, 0);
 	}
-- 
2.39.2

[PATCH 08/16] zram: rename __zram_bvec_read to zram_read_page

[Christoph Hellwig]

__zram_bvec_read doesn't get passed a bvec, but always read a whole
page.  Rename it to make the usage more clear.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0e91e94f24cd09..6187e41a346fd8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1403,8 +1403,8 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 	return ret;
 }
 
-static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
-			    struct bio *bio, bool partial_io)
+static int zram_read_page(struct zram *zram, struct page *page, u32 index,
+			  struct bio *bio, bool partial_io)
 {
 	int ret;
 
@@ -1442,7 +1442,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 			return -ENOMEM;
 	}
 
-	ret = __zram_bvec_read(zram, page, index, bio, is_partial_io(bvec));
+	ret = zram_read_page(zram, page, index, bio, is_partial_io(bvec));
 	if (unlikely(ret))
 		goto out;
 
@@ -1599,7 +1599,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 		if (!page)
 			return -ENOMEM;
 
-		ret = __zram_bvec_read(zram, page, index, bio, true);
+		ret = zram_read_page(zram, page, index, bio, true);
 		if (ret)
 			goto out;
 
-- 
2.39.2

[PATCH 09/16] zram: directly call zram_read_page in writeback_store

[Christoph Hellwig]

writeback_store always reads a full page, so just call zram_read_page
directly and bypass the boune buffer handling.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 6187e41a346fd8..9d2b6ef4638903 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -54,9 +54,8 @@ static size_t huge_class_size;
 static const struct block_device_operations zram_devops;
 
 static void zram_free_page(struct zram *zram, size_t index);
-static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
-				u32 index, int offset, struct bio *bio);
-
+static int zram_read_page(struct zram *zram, struct page *page, u32 index,
+			  struct bio *bio, bool partial_io);
 
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
@@ -671,10 +670,6 @@ static ssize_t writeback_store(struct device *dev,
 	}
 
 	for (; nr_pages != 0; index++, nr_pages--) {
-		struct bio_vec bvec;
-
-		bvec_set_page(&bvec, page, PAGE_SIZE, 0);
-
 		spin_lock(&zram->wb_limit_lock);
 		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
 			spin_unlock(&zram->wb_limit_lock);
@@ -718,7 +713,7 @@ static ssize_t writeback_store(struct device *dev,
 		/* Need for hugepage writeback racing */
 		zram_set_flag(zram, index, ZRAM_IDLE);
 		zram_slot_unlock(zram, index);
-		if (zram_bvec_read(zram, &bvec, index, 0, NULL)) {
+		if (zram_read_page(zram, page, index, NULL, false)) {
 			zram_slot_lock(zram, index);
 			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
 			zram_clear_flag(zram, index, ZRAM_IDLE);
@@ -729,9 +724,8 @@ static ssize_t writeback_store(struct device *dev,
 		bio_init(&bio, zram->bdev, &bio_vec, 1,
 			 REQ_OP_WRITE | REQ_SYNC);
 		bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
-
-		bio_add_page(&bio, bvec.bv_page, bvec.bv_len,
-				bvec.bv_offset);
+		bio_add_page(&bio, page, PAGE_SIZE, 0);
+	
 		/*
 		 * XXX: A single page IO would be inefficient for write
 		 * but it would be not bad as starter.
-- 
2.39.2

[PATCH 10/16] zram: refactor zram_bdev_read

[Christoph Hellwig]

Split the partial read into a separate helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 40 +++++++++++++++++------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9d2b6ef4638903..1d32290cd6d995 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1422,33 +1422,33 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 	return ret;
 }
 
-static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
-			  u32 index, int offset, struct bio *bio)
+/*
+ * Use a temporary buffer to decompress the page, as the decompressor
+ * always expects a full page for the output.
+ */
+static int zram_bvec_read_partial(struct zram *zram, struct bio_vec *bvec,
+				  u32 index, int offset, struct bio *bio)
 {
+	struct page *page = alloc_page(GFP_NOIO);
 	int ret;
-	struct page *page;
-
-	page = bvec->bv_page;
-	if (is_partial_io(bvec)) {
-		/* Use a temporary buffer to decompress the page */
-		page = alloc_page(GFP_NOIO);
-		if (!page)
-			return -ENOMEM;
-	}
-
-	ret = zram_read_page(zram, page, index, bio, is_partial_io(bvec));
-	if (unlikely(ret))
-		goto out;
 
-	if (is_partial_io(bvec))
+	if (!page)
+		return -ENOMEM;
+	ret = zram_read_page(zram, page, index, bio, true);
+	if (likely(!ret))
 		memcpy_to_bvec(bvec, page_address(page) + offset);
-out:
-	if (is_partial_io(bvec))
-		__free_page(page);
-
+	__free_page(page);
 	return ret;
 }
 
+static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
+			  u32 index, int offset, struct bio *bio)
+{
+	if (is_partial_io(bvec))
+		return zram_bvec_read_partial(zram, bvec, index, offset, bio);
+	return zram_read_page(zram, bvec->bv_page, index, bio, false);
+}
+
 static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 				u32 index, struct bio *bio)
 {
-- 
2.39.2

[PATCH 11/16] zram: don't pass a bvec to __zram_bvec_write

[Christoph Hellwig]

__zram_bvec_write only extracts the page from __zram_bvec_write and
always expects a full page of input.  Pass the page directly instead
of the bvec and rename the function to zram_write_bvec.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1d32290cd6d995..1706462495edda 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1449,8 +1449,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	return zram_read_page(zram, bvec->bv_page, index, bio, false);
 }
 
-static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
-				u32 index, struct bio *bio)
+static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 {
 	int ret = 0;
 	unsigned long alloced_pages;
@@ -1458,7 +1457,6 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	unsigned int comp_len = 0;
 	void *src, *dst, *mem;
 	struct zcomp_strm *zstrm;
-	struct page *page = bvec->bv_page;
 	unsigned long element = 0;
 	enum zram_pageflags flags = 0;
 
@@ -1579,11 +1577,9 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 				u32 index, int offset, struct bio *bio)
 {
+	struct page *page = bvec->bv_page;
 	int ret;
-	struct page *page = NULL;
-	struct bio_vec vec;
 
-	vec = *bvec;
 	if (is_partial_io(bvec)) {
 		/*
 		 * This is a partial IO. We need to read the full page
@@ -1598,11 +1594,9 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 			goto out;
 
 		memcpy_from_bvec(page_address(page) + offset, bvec);
-
-		bvec_set_page(&vec, page, PAGE_SIZE, 0);
 	}
 
-	ret = __zram_bvec_write(zram, &vec, index, bio);
+	ret = zram_write_page(zram, page, index);
 out:
 	if (is_partial_io(bvec))
 		__free_page(page);
@@ -1717,7 +1711,7 @@ static int zram_recompress(struct zram *zram, u32 index, struct page *page,
 
 	/*
 	 * No direct reclaim (slow path) for handle allocation and no
-	 * re-compression attempt (unlike in __zram_bvec_write()) since
+	 * re-compression attempt (unlike in zram_write_bvec()) since
 	 * we already have stored that object in zsmalloc. If we cannot
 	 * alloc memory for recompressed object then we bail out and
 	 * simply keep the old (existing) object in zsmalloc.
-- 
2.39.2

[PATCH 12/16] zram: refactor zram_bdev_write

[Christoph Hellwig]

Split the read/modify/write case into a separate helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 38 +++++++++++++++++------------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 1706462495edda..9a3bee1dda01c0 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1574,33 +1574,33 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	return ret;
 }
 
-static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
-				u32 index, int offset, struct bio *bio)
+/*
+ * This is a partial IO.  Read the full page before to writing the changes.
+ */
+static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
+				   u32 index, int offset, struct bio *bio)
 {
-	struct page *page = bvec->bv_page;
+	struct page *page = alloc_page(GFP_NOIO);
 	int ret;
 
-	if (is_partial_io(bvec)) {
-		/*
-		 * This is a partial IO. We need to read the full page
-		 * before to write the changes.
-		 */
-		page = alloc_page(GFP_NOIO);
-		if (!page)
-			return -ENOMEM;
-
-		ret = zram_read_page(zram, page, index, bio, true);
-		if (ret)
-			goto out;
+	if (!page)
+		return -ENOMEM;
 
+	ret = zram_read_page(zram, page, index, bio, true);
+	if (!ret) {
 		memcpy_from_bvec(page_address(page) + offset, bvec);
+		ret = zram_write_page(zram, page, index);
 	}
+	__free_page(page);
+	return ret;
+}
 
-	ret = zram_write_page(zram, page, index);
-out:
+static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
+			   u32 index, int offset, struct bio *bio)
+{
 	if (is_partial_io(bvec))
-		__free_page(page);
-	return ret;
+		return zram_bvec_write_partial(zram, bvec, index, offset, bio);
+	return zram_write_page(zram, bvec->bv_page, index);
 }
 
 #ifdef CONFIG_ZRAM_MULTI_COMP
-- 
2.39.2

[PATCH 13/16] zram: pass a page to read_from_bdev

[Christoph Hellwig]

read_from_bdev always reads a whole page, so pass a page to it instead
of the bvec and remove the now pointless zram_bvec_read_from_bdev
wrapper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 46 +++++++++++++----------------------
 1 file changed, 17 insertions(+), 29 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9a3bee1dda01c0..762f617d8ba9ad 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -587,7 +587,7 @@ static void zram_page_end_io(struct bio *bio)
 /*
  * Returns 1 if the submission is successful.
  */
-static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev_async(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent)
 {
 	struct bio *bio;
@@ -598,7 +598,7 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
 		return -ENOMEM;
 
 	bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
-	if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len, bvec->bv_offset)) {
+	if (!bio_add_page(bio, page, PAGE_SIZE, 0)) {
 		bio_put(bio);
 		return -EIO;
 	}
@@ -794,7 +794,7 @@ struct zram_work {
 	struct zram *zram;
 	unsigned long entry;
 	struct bio *bio;
-	struct bio_vec bvec;
+	struct page *page;
 };
 
 #if PAGE_SIZE != 4096
@@ -805,7 +805,7 @@ static void zram_sync_read(struct work_struct *work)
 	unsigned long entry = zw->entry;
 	struct bio *bio = zw->bio;
 
-	read_from_bdev_async(zram, &zw->bvec, entry, bio);
+	read_from_bdev_async(zram, zw->page, entry, bio);
 }
 
 /*
@@ -813,12 +813,12 @@ static void zram_sync_read(struct work_struct *work)
  * chained IO with parent IO in same context, it's a deadlock. To avoid that,
  * use a worker thread context.
  */
-static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev_sync(struct zram *zram, struct page *page,
 				unsigned long entry, struct bio *bio)
 {
 	struct zram_work work;
 
-	work.bvec = *bvec;
+	work.page = page;
 	work.zram = zram;
 	work.entry = entry;
 	work.bio = bio;
@@ -831,7 +831,7 @@ static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
 	return 1;
 }
 #else
-static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev_sync(struct zram *zram, struct page *page,
 				unsigned long entry, struct bio *bio)
 {
 	WARN_ON(1);
@@ -839,18 +839,17 @@ static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
 }
 #endif
 
-static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent, bool sync)
 {
 	atomic64_inc(&zram->stats.bd_reads);
 	if (sync)
-		return read_from_bdev_sync(zram, bvec, entry, parent);
-	else
-		return read_from_bdev_async(zram, bvec, entry, parent);
+		return read_from_bdev_sync(zram, page, entry, parent);
+	return read_from_bdev_async(zram, page, entry, parent);
 }
 #else
 static inline void reset_bdev(struct zram *zram) {};
-static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
+static int read_from_bdev(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent, bool sync)
 {
 	return -EIO;
@@ -1334,20 +1333,6 @@ static void zram_free_page(struct zram *zram, size_t index)
 		~(1UL << ZRAM_LOCK | 1UL << ZRAM_UNDER_WB));
 }
 
-/*
- * Reads a page from the writeback devices. Corresponding ZRAM slot
- * should be unlocked.
- */
-static int zram_bvec_read_from_bdev(struct zram *zram, struct page *page,
-				    u32 index, struct bio *bio, bool partial_io)
-{
-	struct bio_vec bvec;
-
-	bvec_set_page(&bvec, page, PAGE_SIZE, 0);
-	return read_from_bdev(zram, &bvec, zram_get_element(zram, index), bio,
-			      partial_io);
-}
-
 /*
  * Reads (decompresses if needed) a page from zspool (zsmalloc).
  * Corresponding ZRAM slot should be locked.
@@ -1408,11 +1393,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 		ret = zram_read_from_zspool(zram, page, index);
 		zram_slot_unlock(zram, index);
 	} else {
-		/* Slot should be unlocked before the function call */
+		/*
+		 * The slot should be unlocked before reading from the backing
+		 * device.
+		 */
 		zram_slot_unlock(zram, index);
 
-		ret = zram_bvec_read_from_bdev(zram, page, index, bio,
-					       partial_io);
+		ret = read_from_bdev(zram, page, zram_get_element(zram, index),
+				     bio, partial_io);
 	}
 
 	/* Should NEVER happen. Return bio error if it does. */
-- 
2.39.2

[PATCH 14/16] zram: don't return errors from read_from_bdev_async

[Christoph Hellwig]

bio_alloc will never return a NULL bio when it is allowed to sleep,
and adding a single page to bio with a single vector also can't
fail, so switch to the asserting __bio_add_page variant and drop the
error returns.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 762f617d8ba9ad..b9b14165e651f9 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -584,24 +584,16 @@ static void zram_page_end_io(struct bio *bio)
 	bio_put(bio);
 }
 
-/*
- * Returns 1 if the submission is successful.
- */
-static int read_from_bdev_async(struct zram *zram, struct page *page,
+static void read_from_bdev_async(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent)
 {
 	struct bio *bio;
 
 	bio = bio_alloc(zram->bdev, 1, parent ? parent->bi_opf : REQ_OP_READ,
 			GFP_NOIO);
-	if (!bio)
-		return -ENOMEM;
 
 	bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
-	if (!bio_add_page(bio, page, PAGE_SIZE, 0)) {
-		bio_put(bio);
-		return -EIO;
-	}
+	__bio_add_page(bio, page, PAGE_SIZE, 0);
 
 	if (!parent)
 		bio->bi_end_io = zram_page_end_io;
@@ -609,7 +601,6 @@ static int read_from_bdev_async(struct zram *zram, struct page *page,
 		bio_chain(bio, parent);
 
 	submit_bio(bio);
-	return 1;
 }
 
 #define PAGE_WB_SIG "page_index="
@@ -845,7 +836,8 @@ static int read_from_bdev(struct zram *zram, struct page *page,
 	atomic64_inc(&zram->stats.bd_reads);
 	if (sync)
 		return read_from_bdev_sync(zram, page, entry, parent);
-	return read_from_bdev_async(zram, page, entry, parent);
+	read_from_bdev_async(zram, page, entry, parent);
+	return 1;
 }
 #else
 static inline void reset_bdev(struct zram *zram) {};
-- 
2.39.2

[PATCH 15/16] zram: fix synchronous reads

[Christoph Hellwig]

Currently nothing waits for the synchronous reads before accessing
the data.  Switch them to an on-stack bio and submit_bio_wait to
make sure the I/O has actually completed when the work item has been
flushed.  This also removes the call to page_endio that would unlock
a page that has never been locked.

Drop the partial_io/sync flag, as chaining only makes sense for the
asynchronous reads of the entire page.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 64 +++++++++++++----------------------
 1 file changed, 24 insertions(+), 40 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index b9b14165e651f9..0a98a0ba14607a 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -55,7 +55,7 @@ static const struct block_device_operations zram_devops;
 
 static void zram_free_page(struct zram *zram, size_t index);
 static int zram_read_page(struct zram *zram, struct page *page, u32 index,
-			  struct bio *bio, bool partial_io);
+			  struct bio *parent);
 
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
@@ -575,31 +575,15 @@ static void free_block_bdev(struct zram *zram, unsigned long blk_idx)
 	atomic64_dec(&zram->stats.bd_count);
 }
 
-static void zram_page_end_io(struct bio *bio)
-{
-	struct page *page = bio_first_page_all(bio);
-
-	page_endio(page, op_is_write(bio_op(bio)),
-			blk_status_to_errno(bio->bi_status));
-	bio_put(bio);
-}
-
 static void read_from_bdev_async(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent)
 {
 	struct bio *bio;
 
-	bio = bio_alloc(zram->bdev, 1, parent ? parent->bi_opf : REQ_OP_READ,
-			GFP_NOIO);
-
+	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);
-
-	if (!parent)
-		bio->bi_end_io = zram_page_end_io;
-	else
-		bio_chain(bio, parent);
-
+	bio_chain(bio, parent);
 	submit_bio(bio);
 }
 
@@ -704,7 +688,7 @@ static ssize_t writeback_store(struct device *dev,
 		/* Need for hugepage writeback racing */
 		zram_set_flag(zram, index, ZRAM_IDLE);
 		zram_slot_unlock(zram, index);
-		if (zram_read_page(zram, page, index, NULL, false)) {
+		if (zram_read_page(zram, page, index, NULL)) {
 			zram_slot_lock(zram, index);
 			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
 			zram_clear_flag(zram, index, ZRAM_IDLE);
@@ -780,23 +764,24 @@ static ssize_t writeback_store(struct device *dev,
 	return ret;
 }
 
+#if PAGE_SIZE != 4096
 struct zram_work {
 	struct work_struct work;
 	struct zram *zram;
 	unsigned long entry;
-	struct bio *bio;
 	struct page *page;
 };
 
-#if PAGE_SIZE != 4096
 static void zram_sync_read(struct work_struct *work)
 {
 	struct zram_work *zw = container_of(work, struct zram_work, work);
-	struct zram *zram = zw->zram;
-	unsigned long entry = zw->entry;
-	struct bio *bio = zw->bio;
+	struct bio_bvec bv;
+	struct bio bio;
 
-	read_from_bdev_async(zram, zw->page, entry, bio);
+	bio_init(&bio, zw->zram->bdev, &bv, 1, REQ_OP_READ);
+	bio.bi_iter.bi_sector = zw->entry * (PAGE_SIZE >> 9);
+	__bio_add_page(&bio, zw->page, PAGE_SIZE, 0);
+	submit_bio_wait(&bio);
 }
 
 /*
@@ -805,14 +790,13 @@ static void zram_sync_read(struct work_struct *work)
  * use a worker thread context.
  */
 static int read_from_bdev_sync(struct zram *zram, struct page *page,
-				unsigned long entry, struct bio *bio)
+				unsigned long entry)
 {
 	struct zram_work work;
 
 	work.page = page;
 	work.zram = zram;
 	work.entry = entry;
-	work.bio = bio;
 
 	INIT_WORK_ONSTACK(&work.work, zram_sync_read);
 	queue_work(system_unbound_wq, &work.work);
@@ -823,7 +807,7 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 }
 #else
 static int read_from_bdev_sync(struct zram *zram, struct page *page,
-				unsigned long entry, struct bio *bio)
+				unsigned long entry)
 {
 	WARN_ON(1);
 	return -EIO;
@@ -831,18 +815,18 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 #endif
 
 static int read_from_bdev(struct zram *zram, struct page *page,
-			unsigned long entry, struct bio *parent, bool sync)
+			unsigned long entry, struct bio *parent)
 {
 	atomic64_inc(&zram->stats.bd_reads);
-	if (sync)
-		return read_from_bdev_sync(zram, page, entry, parent);
+	if (!parent)
+		return read_from_bdev_sync(zram, page, entry);
 	read_from_bdev_async(zram, page, entry, parent);
 	return 1;
 }
 #else
 static inline void reset_bdev(struct zram *zram) {};
 static int read_from_bdev(struct zram *zram, struct page *page,
-			unsigned long entry, struct bio *parent, bool sync)
+			unsigned long entry, struct bio *parent)
 {
 	return -EIO;
 }
@@ -1375,7 +1359,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 }
 
 static int zram_read_page(struct zram *zram, struct page *page, u32 index,
-			  struct bio *bio, bool partial_io)
+			  struct bio *parent)
 {
 	int ret;
 
@@ -1392,7 +1376,7 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 		zram_slot_unlock(zram, index);
 
 		ret = read_from_bdev(zram, page, zram_get_element(zram, index),
-				     bio, partial_io);
+				     parent);
 	}
 
 	/* Should NEVER happen. Return bio error if it does. */
@@ -1407,14 +1391,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
  * always expects a full page for the output.
  */
 static int zram_bvec_read_partial(struct zram *zram, struct bio_vec *bvec,
-				  u32 index, int offset, struct bio *bio)
+				  u32 index, int offset)
 {
 	struct page *page = alloc_page(GFP_NOIO);
 	int ret;
 
 	if (!page)
 		return -ENOMEM;
-	ret = zram_read_page(zram, page, index, bio, true);
+	ret = zram_read_page(zram, page, index, NULL);
 	if (likely(!ret))
 		memcpy_to_bvec(bvec, page_address(page) + offset);
 	__free_page(page);
@@ -1425,8 +1409,8 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 			  u32 index, int offset, struct bio *bio)
 {
 	if (is_partial_io(bvec))
-		return zram_bvec_read_partial(zram, bvec, index, offset, bio);
-	return zram_read_page(zram, bvec->bv_page, index, bio, false);
+		return zram_bvec_read_partial(zram, bvec, index, offset);
+	return zram_read_page(zram, bvec->bv_page, index, bio);
 }
 
 static int zram_write_page(struct zram *zram, struct page *page, u32 index)
@@ -1566,7 +1550,7 @@ static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
 	if (!page)
 		return -ENOMEM;
 
-	ret = zram_read_page(zram, page, index, bio, true);
+	ret = zram_read_page(zram, page, index, bio);
 	if (!ret) {
 		memcpy_from_bvec(page_address(page) + offset, bvec);
 		ret = zram_write_page(zram, page, index);
-- 
2.39.2

[PATCH 16/16] zram: return errors from read_from_bdev_sync

[Christoph Hellwig]

Propagate read errors to the caller instead of dropping them on
the floor, and stop returning the somewhat dangerous 1 on success
from read_from_bdev*.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/zram/zram_drv.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0a98a0ba14607a..0be1633b0f4e94 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -770,6 +770,7 @@ struct zram_work {
 	struct zram *zram;
 	unsigned long entry;
 	struct page *page;
+	int error;
 };
 
 static void zram_sync_read(struct work_struct *work)
@@ -781,7 +782,7 @@ static void zram_sync_read(struct work_struct *work)
 	bio_init(&bio, zw->zram->bdev, &bv, 1, REQ_OP_READ);
 	bio.bi_iter.bi_sector = zw->entry * (PAGE_SIZE >> 9);
 	__bio_add_page(&bio, zw->page, PAGE_SIZE, 0);
-	submit_bio_wait(&bio);
+	zw->error = submit_bio_wait(&bio);
 }
 
 /*
@@ -803,7 +804,7 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 	flush_work(&work.work);
 	destroy_work_on_stack(&work.work);
 
-	return 1;
+	return work.error;
 }
 #else
 static int read_from_bdev_sync(struct zram *zram, struct page *page,
@@ -821,7 +822,7 @@ static int read_from_bdev(struct zram *zram, struct page *page,
 	if (!parent)
 		return read_from_bdev_sync(zram, page, entry);
 	read_from_bdev_async(zram, page, entry, parent);
-	return 1;
+	return 0;
 }
 #else
 static inline void reset_bdev(struct zram *zram) {};
-- 
2.39.2

Re: [PATCH 01/16] zram: remove valid_io_request

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> All bios hande to drivers from the block layer are checked against the
> device size and for logical block alignment already, so don't duplicate
> those checks.

Has this changed "recently"? I can trace that valid_io() function back
to initial zram commit 306b0c957f3f0e7 (Staging: virtual block device
driver (ramzswap)). Was that check always redundant?

Re: [PATCH 02/16] zram: make zram_bio_discard more self-contained

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> Derive the index and offset variables inside the function, and complete
> the bio directly in preparation for cleaning up the I/O path.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 03/16] zram: implify bvec iteration in __zram_make_request

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> bio_for_each_segment synthetize bvecs that never cross page boundaries,
> so don't duplicate that work in an inner loop.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 04/16] zram: move discard handling to zram_submit_bio

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> Switch on the bio operation in zram_submit_bio and only call into
> __zram_make_request for read and write operations.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

[..]
> @@ -1996,7 +1987,19 @@ static void zram_submit_bio(struct bio *bio)
>  {
>  	struct zram *zram = bio->bi_bdev->bd_disk->private_data;
>  
> -	__zram_make_request(zram, bio);
> +	switch (bio_op(bio)) {
> +	case REQ_OP_READ:
> +	case REQ_OP_WRITE:
> +		__zram_make_request(zram, bio);
> +		break;
> +	case REQ_OP_DISCARD:
> +	case REQ_OP_WRITE_ZEROES:
> +		zram_bio_discard(zram, bio);
> +		return;

Super nitpick,  break;

> +	default:
> +		WARN_ON_ONCE(1);
> +		bio_endio(bio);
> +	}
>  }
>  
>  static void zram_slot_free_notify(struct block_device *bdev,
> -- 
> 2.39.2
> 

Re: [PATCH 05/16] zram: return early on error in zram_bvec_rw

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> @@ -1939,23 +1939,23 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
>  
>  	if (!op_is_write(op)) {
>  		ret = zram_bvec_read(zram, bvec, index, offset, bio);
> +		if (unlikely(ret < 0)) {
> +			atomic64_inc(&zram->stats.failed_writes);

This is !op_is_write() so we need to increment ->failed_reads

> +			return ret;
> +		}
>  		flush_dcache_page(bvec->bv_page);
>  	} else {
>  		ret = zram_bvec_write(zram, bvec, index, offset, bio);
> +		if (unlikely(ret < 0)) {
> +			atomic64_inc(&zram->stats.failed_reads);

and ->failed_writes here.

> +			return ret;
> +		}
>  	}

Re: [PATCH 06/16] zram: refactor highlevel read and write handling

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> +static void zram_bio_read(struct zram *zram, struct bio *bio)
>  {
> -	int ret;
> +	struct bvec_iter iter;
> +	struct bio_vec bv;
> +	unsigned long start_time;
>  
> -	if (!op_is_write(op)) {
> -		ret = zram_bvec_read(zram, bvec, index, offset, bio);
> -		if (unlikely(ret < 0)) {
> +	start_time = bio_start_io_acct(bio);
> +	bio_for_each_segment(bv, bio, iter) {
> +		u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
> +		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
> +				SECTOR_SHIFT;
> +
> +		if (zram_bvec_read(zram, &bv, index, offset, bio) < 0) {
>  			atomic64_inc(&zram->stats.failed_writes);

						->failed_reads

> -			return ret;
> -		}
> -		flush_dcache_page(bvec->bv_page);
> -	} else {
> -		ret = zram_bvec_write(zram, bvec, index, offset, bio);
> -		if (unlikely(ret < 0)) {
> -			atomic64_inc(&zram->stats.failed_reads);
> -			return ret;
> +			bio->bi_status = BLK_STS_IOERR;
> +			break;
>  		}
> -	}
> +		flush_dcache_page(bv.bv_page);
>  
> -	zram_slot_lock(zram, index);
> -	zram_accessed(zram, index);
> -	zram_slot_unlock(zram, index);
> -	return 0;
> +		zram_slot_lock(zram, index);
> +		zram_accessed(zram, index);
> +		zram_slot_unlock(zram, index);
> +	}
> +	bio_end_io_acct(bio, start_time);
> +	bio_endio(bio);
>  }
>  
> -static void __zram_make_request(struct zram *zram, struct bio *bio)
> +static void zram_bio_write(struct zram *zram, struct bio *bio)
>  {
>  	struct bvec_iter iter;
>  	struct bio_vec bv;
> @@ -1970,11 +1966,15 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
>  		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
>  				SECTOR_SHIFT;
>  
> -		if (zram_bvec_rw(zram, &bv, index, offset, bio_op(bio),
> -				bio) < 0) {
> +		if (zram_bvec_write(zram, &bv, index, offset, bio) < 0) {
> +			atomic64_inc(&zram->stats.failed_reads);

						->failed_writes

>  			bio->bi_status = BLK_STS_IOERR;
>  			break;
>  		}
> +
> +		zram_slot_lock(zram, index);
> +		zram_accessed(zram, index);
> +		zram_slot_unlock(zram, index);
>  	}
>  	bio_end_io_acct(bio, start_time);
>  	bio_endio(bio);
> @@ -1989,8 +1989,10 @@ static void zram_submit_bio(struct bio *bio)
>  
>  	switch (bio_op(bio)) {
>  	case REQ_OP_READ:
> +		zram_bio_read(zram, bio);
> +		break;
>  	case REQ_OP_WRITE:
> -		__zram_make_request(zram, bio);
> +		zram_bio_write(zram, bio);
>  		break;
>  	case REQ_OP_DISCARD:
>  	case REQ_OP_WRITE_ZEROES:
> -- 
> 2.39.2
> 

Re: [PATCH 07/16] zram: don't use highmem for the bounce buffer in zram_bvec_{read,write}

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> There is no point in allocation a highmem page when we instantly need
> to copy from it.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Makes sense to me

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

Re: [PATCH 08/16] zram: rename __zram_bvec_read to zram_read_page

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> __zram_bvec_read doesn't get passed a bvec, but always read a whole
> page.  Rename it to make the usage more clear.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 09/16] zram: directly call zram_read_page in writeback_store

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> writeback_store always reads a full page, so just call zram_read_page
> directly and bypass the boune buffer handling.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

> ---
>  drivers/block/zram/zram_drv.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 6187e41a346fd8..9d2b6ef4638903 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -54,9 +54,8 @@ static size_t huge_class_size;
>  static const struct block_device_operations zram_devops;
>  
>  static void zram_free_page(struct zram *zram, size_t index);
> -static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> -				u32 index, int offset, struct bio *bio);
> -
> +static int zram_read_page(struct zram *zram, struct page *page, u32 index,
> +			  struct bio *bio, bool partial_io);
>  
>  static int zram_slot_trylock(struct zram *zram, u32 index)
>  {
> @@ -671,10 +670,6 @@ static ssize_t writeback_store(struct device *dev,
>  	}
>  
>  	for (; nr_pages != 0; index++, nr_pages--) {
> -		struct bio_vec bvec;
> -
> -		bvec_set_page(&bvec, page, PAGE_SIZE, 0);
> -
>  		spin_lock(&zram->wb_limit_lock);
>  		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
>  			spin_unlock(&zram->wb_limit_lock);
> @@ -718,7 +713,7 @@ static ssize_t writeback_store(struct device *dev,
>  		/* Need for hugepage writeback racing */
>  		zram_set_flag(zram, index, ZRAM_IDLE);
>  		zram_slot_unlock(zram, index);
> -		if (zram_bvec_read(zram, &bvec, index, 0, NULL)) {
> +		if (zram_read_page(zram, page, index, NULL, false)) {

In theory we can call zram_read_from_zspool() here, but zram_read_page()
is fine with me.

>  			zram_slot_lock(zram, index);
>  			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
>  			zram_clear_flag(zram, index, ZRAM_IDLE);
> @@ -729,9 +724,8 @@ static ssize_t writeback_store(struct device *dev,
>  		bio_init(&bio, zram->bdev, &bio_vec, 1,
>  			 REQ_OP_WRITE | REQ_SYNC);
>  		bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
> -
> -		bio_add_page(&bio, bvec.bv_page, bvec.bv_len,
> -				bvec.bv_offset);
> +		bio_add_page(&bio, page, PAGE_SIZE, 0);
> +	
>  		/*
>  		 * XXX: A single page IO would be inefficient for write
>  		 * but it would be not bad as starter.
> -- 
> 2.39.2
> 

Re: [PATCH 10/16] zram: refactor zram_bdev_read

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> Split the partial read into a separate helper.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 11/16] zram: don't pass a bvec to __zram_bvec_write

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> __zram_bvec_write only extracts the page from __zram_bvec_write and
> always expects a full page of input.  Pass the page directly instead
> of the bvec and rename the function to zram_write_bvec.

					^^^ zram_write_page()

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

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

Re: [PATCH 12/16] zram: refactor zram_bdev_write

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> -static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
> -				u32 index, int offset, struct bio *bio)
> +/*
> + * This is a partial IO.  Read the full page before to writing the changes.

A super nit: 		double spaces and "before writing"?

Re: [PATCH 14/16] zram: don't return errors from read_from_bdev_async

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> bio_alloc will never return a NULL bio when it is allowed to sleep,
> and adding a single page to bio with a single vector also can't
> fail, so switch to the asserting __bio_add_page variant and drop the
> error returns.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 13/16] zram: pass a page to read_from_bdev

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> read_from_bdev always reads a whole page, so pass a page to it instead
> of the bvec and remove the now pointless zram_bvec_read_from_bdev
> wrapper.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 16/16] zram: return errors from read_from_bdev_sync

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> Propagate read errors to the caller instead of dropping them on
> the floor, and stop returning the somewhat dangerous 1 on success
> from read_from_bdev*.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: [PATCH 01/16] zram: remove valid_io_request

[Christoph Hellwig]

On Thu, Apr 06, 2023 at 10:44:49AM +0900, Sergey Senozhatsky wrote:
> On (23/04/04 17:05), Christoph Hellwig wrote:
> > All bios hande to drivers from the block layer are checked against the
> > device size and for logical block alignment already, so don't duplicate
> > those checks.
> 
> Has this changed "recently"? I can trace that valid_io() function back
> to initial zram commit 306b0c957f3f0e7 (Staging: virtual block device
> driver (ramzswap)). Was that check always redundant?

It was always redundant.

Re: [PATCH 03/16] zram: implify bvec iteration in __zram_make_request

[Christoph Hellwig]

self nit:  there is a s missing in simplify in the Subject.

Re: [PATCH 12/16] zram: refactor zram_bdev_write

[Christoph Hellwig]

On Thu, Apr 06, 2023 at 02:15:05PM +0900, Sergey Senozhatsky wrote:
> > -static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
> > -				u32 index, int offset, struct bio *bio)
> > +/*
> > + * This is a partial IO.  Read the full page before to writing the changes.
> 
> A super nit: 		double spaces and "before writing"?

double space afrer . is the usual style more monospace fonts such
as code.  The to is indeed superflous and a leftover from the previous
comment.

Re: [PATCH 01/16] zram: remove valid_io_request

[Sergey Senozhatsky]

On (23/04/05 22:39), Christoph Hellwig wrote:
> On Thu, Apr 06, 2023 at 10:44:49AM +0900, Sergey Senozhatsky wrote:
> > On (23/04/04 17:05), Christoph Hellwig wrote:
> > > All bios hande to drivers from the block layer are checked against the
> > > device size and for logical block alignment already, so don't duplicate
> > > those checks.
> > 
> > Has this changed "recently"? I can trace that valid_io() function back
> > to initial zram commit 306b0c957f3f0e7 (Staging: virtual block device
> > driver (ramzswap)). Was that check always redundant?
> 
> It was always redundant.

OK, thanks.

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

Re: [PATCH 12/16] zram: refactor zram_bdev_write

[Sergey Senozhatsky]

On (23/04/05 22:45), Christoph Hellwig wrote:
> On Thu, Apr 06, 2023 at 02:15:05PM +0900, Sergey Senozhatsky wrote:
> > > -static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
> > > -				u32 index, int offset, struct bio *bio)
> > > +/*
> > > + * This is a partial IO.  Read the full page before to writing the changes.
> > 
> > A super nit: 		double spaces and "before writing"?
> 
> double space afrer . is the usual style more monospace fonts such
> as code.  

OK, yeah I've noticed that in the commit messages as well.

Re: [PATCH 15/16] zram: fix synchronous reads

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> Currently nothing waits for the synchronous reads before accessing
> the data.  Switch them to an on-stack bio and submit_bio_wait to
> make sure the I/O has actually completed when the work item has been
> flushed.  This also removes the call to page_endio that would unlock
> a page that has never been locked.
> 
> Drop the partial_io/sync flag, as chaining only makes sense for the
> asynchronous reads of the entire page.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

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

Re: zram I/O path cleanups and fixups

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> 
> I don't actually have a large PAGE_SIZE system to test that path on.

Likewise. Don't have a large PAGE_SIZE system, so tested on a 4k x86_64.

Re: zram I/O path cleanups and fixups

[Sergey Senozhatsky]

On (23/04/06 15:43), Sergey Senozhatsky wrote:
> On (23/04/04 17:05), Christoph Hellwig wrote:
> > 
> > I don't actually have a large PAGE_SIZE system to test that path on.
> 
> Likewise. Don't have a large PAGE_SIZE system, so tested on a 4k x86_64.

Hold on... Something isn't right with the writeback test. It doesn't
look like reads of ZRAM_WB pages work.

Re: zram I/O path cleanups and fixups

[Sergey Senozhatsky]

On (23/04/06 15:46), Sergey Senozhatsky wrote:
> On (23/04/06 15:43), Sergey Senozhatsky wrote:
> > On (23/04/04 17:05), Christoph Hellwig wrote:
> > > 
> > > I don't actually have a large PAGE_SIZE system to test that path on.
> > 
> > Likewise. Don't have a large PAGE_SIZE system, so tested on a 4k x86_64.
> 
> Hold on... Something isn't right with the writeback test. It doesn't
> look like reads of ZRAM_WB pages work.

False alarm, sorry for the noise!

Re: zram I/O path cleanups and fixups

[Sergey Senozhatsky]

On (23/04/04 17:05), Christoph Hellwig wrote:
> Hi all,
> 
> this series cleans up the zram I/O path, and fixes the handling of
> synchronous I/O to the underlying device in the writeback_store
> function or for > 4K PAGE_SIZE systems.
> 
> The fixes are at the end, as I could not fully reason about them being
> safe before untangling the callchain.
> 
> This survives xfstests on two zram devices on x86, but I don't actually
> have a large PAGE_SIZE system to test that path on.

Christoph, if you'll do v2 please Cc Andrew on it.

[PATCH 15/16] zram: fix synchronous reads

[Christoph Hellwig]

Currently nothing waits for the synchronous reads before accessing
the data.  Switch them to an on-stack bio and submit_bio_wait to
make sure the I/O has actually completed when the work item has been
flushed.  This also removes the call to page_endio that would unlock
a page that has never been locked.

Drop the partial_io/sync flag, as chaining only makes sense for the
asynchronous reads of the entire page.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 64 +++++++++++++----------------------
 1 file changed, 24 insertions(+), 40 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index ec6df834189b7a..5259b647010afe 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -55,7 +55,7 @@ static const struct block_device_operations zram_devops;
 
 static void zram_free_page(struct zram *zram, size_t index);
 static int zram_read_page(struct zram *zram, struct page *page, u32 index,
-			  struct bio *bio, bool partial_io);
+			  struct bio *parent);
 
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
@@ -575,31 +575,15 @@ static void free_block_bdev(struct zram *zram, unsigned long blk_idx)
 	atomic64_dec(&zram->stats.bd_count);
 }
 
-static void zram_page_end_io(struct bio *bio)
-{
-	struct page *page = bio_first_page_all(bio);
-
-	page_endio(page, op_is_write(bio_op(bio)),
-			blk_status_to_errno(bio->bi_status));
-	bio_put(bio);
-}
-
 static void read_from_bdev_async(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent)
 {
 	struct bio *bio;
 
-	bio = bio_alloc(zram->bdev, 1, parent ? parent->bi_opf : REQ_OP_READ,
-			GFP_NOIO);
-
+	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);
-
-	if (!parent)
-		bio->bi_end_io = zram_page_end_io;
-	else
-		bio_chain(bio, parent);
-
+	bio_chain(bio, parent);
 	submit_bio(bio);
 }
 
@@ -704,7 +688,7 @@ static ssize_t writeback_store(struct device *dev,
 		/* Need for hugepage writeback racing */
 		zram_set_flag(zram, index, ZRAM_IDLE);
 		zram_slot_unlock(zram, index);
-		if (zram_read_page(zram, page, index, NULL, false)) {
+		if (zram_read_page(zram, page, index, NULL)) {
 			zram_slot_lock(zram, index);
 			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
 			zram_clear_flag(zram, index, ZRAM_IDLE);
@@ -780,23 +764,24 @@ static ssize_t writeback_store(struct device *dev,
 	return ret;
 }
 
+#if PAGE_SIZE != 4096
 struct zram_work {
 	struct work_struct work;
 	struct zram *zram;
 	unsigned long entry;
-	struct bio *bio;
 	struct page *page;
 };
 
-#if PAGE_SIZE != 4096
 static void zram_sync_read(struct work_struct *work)
 {
 	struct zram_work *zw = container_of(work, struct zram_work, work);
-	struct zram *zram = zw->zram;
-	unsigned long entry = zw->entry;
-	struct bio *bio = zw->bio;
+	struct bio_bvec bv;
+	struct bio bio;
 
-	read_from_bdev_async(zram, zw->page, entry, bio);
+	bio_init(&bio, zw->zram->bdev, &bv, 1, REQ_OP_READ);
+	bio.bi_iter.bi_sector = zw->entry * (PAGE_SIZE >> 9);
+	__bio_add_page(&bio, zw->page, PAGE_SIZE, 0);
+	submit_bio_wait(&bio);
 }
 
 /*
@@ -805,14 +790,13 @@ static void zram_sync_read(struct work_struct *work)
  * use a worker thread context.
  */
 static int read_from_bdev_sync(struct zram *zram, struct page *page,
-				unsigned long entry, struct bio *bio)
+				unsigned long entry)
 {
 	struct zram_work work;
 
 	work.page = page;
 	work.zram = zram;
 	work.entry = entry;
-	work.bio = bio;
 
 	INIT_WORK_ONSTACK(&work.work, zram_sync_read);
 	queue_work(system_unbound_wq, &work.work);
@@ -823,7 +807,7 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 }
 #else
 static int read_from_bdev_sync(struct zram *zram, struct page *page,
-				unsigned long entry, struct bio *bio)
+				unsigned long entry)
 {
 	WARN_ON(1);
 	return -EIO;
@@ -831,18 +815,18 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 #endif
 
 static int read_from_bdev(struct zram *zram, struct page *page,
-			unsigned long entry, struct bio *parent, bool sync)
+			unsigned long entry, struct bio *parent)
 {
 	atomic64_inc(&zram->stats.bd_reads);
-	if (sync)
-		return read_from_bdev_sync(zram, page, entry, parent);
+	if (!parent)
+		return read_from_bdev_sync(zram, page, entry);
 	read_from_bdev_async(zram, page, entry, parent);
 	return 1;
 }
 #else
 static inline void reset_bdev(struct zram *zram) {};
 static int read_from_bdev(struct zram *zram, struct page *page,
-			unsigned long entry, struct bio *parent, bool sync)
+			unsigned long entry, struct bio *parent)
 {
 	return -EIO;
 }
@@ -1375,7 +1359,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 }
 
 static int zram_read_page(struct zram *zram, struct page *page, u32 index,
-			  struct bio *bio, bool partial_io)
+			  struct bio *parent)
 {
 	int ret;
 
@@ -1392,7 +1376,7 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 		zram_slot_unlock(zram, index);
 
 		ret = read_from_bdev(zram, page, zram_get_element(zram, index),
-				     bio, partial_io);
+				     parent);
 	}
 
 	/* Should NEVER happen. Return bio error if it does. */
@@ -1407,14 +1391,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
  * always expects a full page for the output.
  */
 static int zram_bvec_read_partial(struct zram *zram, struct bio_vec *bvec,
-				  u32 index, int offset, struct bio *bio)
+				  u32 index, int offset)
 {
 	struct page *page = alloc_page(GFP_NOIO);
 	int ret;
 
 	if (!page)
 		return -ENOMEM;
-	ret = zram_read_page(zram, page, index, bio, true);
+	ret = zram_read_page(zram, page, index, NULL);
 	if (likely(!ret))
 		memcpy_to_bvec(bvec, page_address(page) + offset);
 	__free_page(page);
@@ -1425,8 +1409,8 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 			  u32 index, int offset, struct bio *bio)
 {
 	if (is_partial_io(bvec))
-		return zram_bvec_read_partial(zram, bvec, index, offset, bio);
-	return zram_read_page(zram, bvec->bv_page, index, bio, false);
+		return zram_bvec_read_partial(zram, bvec, index, offset);
+	return zram_read_page(zram, bvec->bv_page, index, bio);
 }
 
 static int zram_write_page(struct zram *zram, struct page *page, u32 index)
@@ -1566,7 +1550,7 @@ static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
 	if (!page)
 		return -ENOMEM;
 
-	ret = zram_read_page(zram, page, index, bio, true);
+	ret = zram_read_page(zram, page, index, bio);
 	if (!ret) {
 		memcpy_from_bvec(page_address(page) + offset, bvec);
 		ret = zram_write_page(zram, page, index);
-- 
2.39.2

Re: [PATCH 15/16] zram: fix synchronous reads

[Minchan Kim]

On Thu, Apr 06, 2023 at 04:41:01PM +0200, Christoph Hellwig wrote:
> Currently nothing waits for the synchronous reads before accessing
> the data.  Switch them to an on-stack bio and submit_bio_wait to
> make sure the I/O has actually completed when the work item has been
> flushed.  This also removes the call to page_endio that would unlock
> a page that has never been locked.
> 
> Drop the partial_io/sync flag, as chaining only makes sense for the
> asynchronous reads of the entire page.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>

So this fixes zram_rw_page + CONFIG_ZRAM_WRITEBACK feature on
ppc some arch where PAGE_SIZE is not 4K.

IIRC, we didn't have any report since the writeback feature was
introduced. Then, we may skip having the fix into stable?

Re: [PATCH 15/16] zram: fix synchronous reads

[Andrew Morton]

On Thu, 6 Apr 2023 15:05:22 -0700 Minchan Kim <minchan@kernel.org> wrote:

> On Thu, Apr 06, 2023 at 04:41:01PM +0200, Christoph Hellwig wrote:
> > Currently nothing waits for the synchronous reads before accessing
> > the data.  Switch them to an on-stack bio and submit_bio_wait to
> > make sure the I/O has actually completed when the work item has been
> > flushed.  This also removes the call to page_endio that would unlock
> > a page that has never been locked.
> > 
> > Drop the partial_io/sync flag, as chaining only makes sense for the
> > asynchronous reads of the entire page.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Acked-by: Minchan Kim <minchan@kernel.org>
> 
> So this fixes zram_rw_page + CONFIG_ZRAM_WRITEBACK feature on
> ppc some arch where PAGE_SIZE is not 4K.
> 
> IIRC, we didn't have any report since the writeback feature was
> introduced. Then, we may skip having the fix into stable?

Someone may develop such a use case in the future.  And backporting
this fix will be difficult, unless people backport all the other
patches, which is also difficult.

What are the user-visible effects of this bug?  It sounds like it will
give userspace access to unintialized kernel memory, which isn't good.

Re: [PATCH 15/16] zram: fix synchronous reads

[Minchan Kim]

On Thu, Apr 06, 2023 at 03:58:10PM -0700, Andrew Morton wrote:
> On Thu, 6 Apr 2023 15:05:22 -0700 Minchan Kim <minchan@kernel.org> wrote:
> 
> > On Thu, Apr 06, 2023 at 04:41:01PM +0200, Christoph Hellwig wrote:
> > > Currently nothing waits for the synchronous reads before accessing
> > > the data.  Switch them to an on-stack bio and submit_bio_wait to
> > > make sure the I/O has actually completed when the work item has been
> > > flushed.  This also removes the call to page_endio that would unlock
> > > a page that has never been locked.
> > > 
> > > Drop the partial_io/sync flag, as chaining only makes sense for the
> > > asynchronous reads of the entire page.
> > > 
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> > Acked-by: Minchan Kim <minchan@kernel.org>
> > 
> > So this fixes zram_rw_page + CONFIG_ZRAM_WRITEBACK feature on
> > ppc some arch where PAGE_SIZE is not 4K.
> > 
> > IIRC, we didn't have any report since the writeback feature was
> > introduced. Then, we may skip having the fix into stable?
> 
> Someone may develop such a use case in the future.  And backporting
> this fix will be difficult, unless people backport all the other
> patches, which is also difficult.

I think the simple fix is just bail out for partial IO case from
rw_page path so that bio comes next to serve the rw_page failure.
In the case, zram will always do chained bio so we are fine with
asynchronous IO.

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index b8549c61ff2c..23fa0e03cdc1 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1264,6 +1264,8 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
                struct bio_vec bvec;

                zram_slot_unlock(zram, index);
+               if (partial_io)
+                       return -EAGAIN;

                bvec.bv_page = page;
                bvec.bv_len = PAGE_SIZE;

> 
> What are the user-visible effects of this bug?  It sounds like it will
> give userspace access to unintialized kernel memory, which isn't good.

It's true.

Without better suggestion or objections, I could cook the stable patch.

Re: [PATCH 15/16] zram: fix synchronous reads

[Andrew Morton]

On Thu, 6 Apr 2023 17:23:51 -0700 Minchan Kim <minchan@kernel.org> wrote:

> > Someone may develop such a use case in the future.  And backporting
> > this fix will be difficult, unless people backport all the other
> > patches, which is also difficult.
> 
> I think the simple fix is just bail out for partial IO case from
> rw_page path so that bio comes next to serve the rw_page failure.
> In the case, zram will always do chained bio so we are fine with
> asynchronous IO.
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b8549c61ff2c..23fa0e03cdc1 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1264,6 +1264,8 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
>                 struct bio_vec bvec;
> 
>                 zram_slot_unlock(zram, index);
> +               if (partial_io)
> +                       return -EAGAIN;
> 
>                 bvec.bv_page = page;
>                 bvec.bv_len = PAGE_SIZE;
> 
> > 
> > What are the user-visible effects of this bug?  It sounds like it will
> > give userspace access to unintialized kernel memory, which isn't good.
> 
> It's true.
> 
> Without better suggestion or objections, I could cook the stable patch.

Sounds good to me.  Please don't forget to describe the user-visible
effects and the situation under which they will be observed, etc.

Then I can redo Chritoph's patches on top, so we end up with this
series as-is going forward.

Re: [PATCH 15/16] zram: fix synchronous reads

[Christoph Hellwig]

On Thu, Apr 06, 2023 at 03:05:22PM -0700, Minchan Kim wrote:
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Acked-by: Minchan Kim <minchan@kernel.org>
> 
> So this fixes zram_rw_page + CONFIG_ZRAM_WRITEBACK feature on
> ppc some arch where PAGE_SIZE is not 4K.

Well, zram_rw_page is gone.  But either way I think CONFIG_ZRAM_WRITEBACK
has been broken on > 4k PAGE_SIZE basically since the code was added.

> IIRC, we didn't have any report since the writeback feature was
> introduced. Then, we may skip having the fix into stable?

If you want a stable fix I'd just disable CONFIG_ZRAM_WRITEBACK
for non-4k PAGE_SIZEs there.

Re: [PATCH 15/16] zram: fix synchronous reads

[Christoph Hellwig]

On Thu, Apr 06, 2023 at 05:23:51PM -0700, Minchan Kim wrote:
> rw_page path so that bio comes next to serve the rw_page failure.
> In the case, zram will always do chained bio so we are fine with
> asynchronous IO.
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index b8549c61ff2c..23fa0e03cdc1 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1264,6 +1264,8 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
>                 struct bio_vec bvec;
> 
>                 zram_slot_unlock(zram, index);
> +               if (partial_io)
> +                       return -EAGAIN;
> 
>                 bvec.bv_page = page;
>                 bvec.bv_len = PAGE_SIZE;

What tree is this supposed to apply to?  6.2 already has the
zram_bvec_read_from_bdev helper.


But either way partial_io can be true when called from zram_bvec_write,
where we can't just -EAGAIN as ->submit_bio is not allowed to return
that except for REQ_NOWAIT bios, and even then it needs to be handle
them when submitted without REQ_NOWAIT.

Re: [PATCH 15/16] zram: fix synchronous reads

[kernel test robot]

Hi Christoph,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe-block/for-next]
[also build test ERROR on linus/master v6.3-rc5 next-20230406]
[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/Christoph-Hellwig/zram-make-zram_bio_discard-more-self-contained/20230406-234133
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/20230406144102.149231-16-hch%40lst.de
patch subject: [PATCH 15/16] zram: fix synchronous reads
config: hexagon-randconfig-r024-20230405 (https://download.01.org/0day-ci/archive/20230407/202304071443.4xWaXjV6-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project 2c57868e2e877f73c339796c3374ae660bb77f0d)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/e4596d7c2cf157f5b3d566cb2cc0769c9232a728
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Christoph-Hellwig/zram-make-zram_bio_discard-more-self-contained/20230406-234133
        git checkout e4596d7c2cf157f5b3d566cb2cc0769c9232a728
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash drivers/block/zram/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304071443.4xWaXjV6-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from drivers/block/zram/zram_drv.c:20:
   In file included from include/linux/bio.h:10:
   In file included from include/linux/blk_types.h:10:
   In file included from include/linux/bvec.h:10:
   In file included from include/linux/highmem.h:12:
   In file included from include/linux/hardirq.h:11:
   In file included from ./arch/hexagon/include/generated/asm/hardirq.h:1:
   In file included from include/asm-generic/hardirq.h:17:
   In file included from include/linux/irq.h:20:
   In file included from include/linux/io.h:13:
   In file included from arch/hexagon/include/asm/io.h:334:
   include/asm-generic/io.h:547:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __raw_readb(PCI_IOBASE + addr);
                             ~~~~~~~~~~ ^
   include/asm-generic/io.h:560:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/little_endian.h:37:51: note: expanded from macro '__le16_to_cpu'
   #define __le16_to_cpu(x) ((__force __u16)(__le16)(x))
                                                     ^
   In file included from drivers/block/zram/zram_drv.c:20:
   In file included from include/linux/bio.h:10:
   In file included from include/linux/blk_types.h:10:
   In file included from include/linux/bvec.h:10:
   In file included from include/linux/highmem.h:12:
   In file included from include/linux/hardirq.h:11:
   In file included from ./arch/hexagon/include/generated/asm/hardirq.h:1:
   In file included from include/asm-generic/hardirq.h:17:
   In file included from include/linux/irq.h:20:
   In file included from include/linux/io.h:13:
   In file included from arch/hexagon/include/asm/io.h:334:
   include/asm-generic/io.h:573:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/little_endian.h:35:51: note: expanded from macro '__le32_to_cpu'
   #define __le32_to_cpu(x) ((__force __u32)(__le32)(x))
                                                     ^
   In file included from drivers/block/zram/zram_drv.c:20:
   In file included from include/linux/bio.h:10:
   In file included from include/linux/blk_types.h:10:
   In file included from include/linux/bvec.h:10:
   In file included from include/linux/highmem.h:12:
   In file included from include/linux/hardirq.h:11:
   In file included from ./arch/hexagon/include/generated/asm/hardirq.h:1:
   In file included from include/asm-generic/hardirq.h:17:
   In file included from include/linux/irq.h:20:
   In file included from include/linux/io.h:13:
   In file included from arch/hexagon/include/asm/io.h:334:
   include/asm-generic/io.h:584:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writeb(value, PCI_IOBASE + addr);
                               ~~~~~~~~~~ ^
   include/asm-generic/io.h:594:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:604:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
>> drivers/block/zram/zram_drv.c:778:18: error: variable has incomplete type 'struct bio_bvec'
           struct bio_bvec bv;
                           ^
   drivers/block/zram/zram_drv.c:778:9: note: forward declaration of 'struct bio_bvec'
           struct bio_bvec bv;
                  ^
   6 warnings and 1 error generated.


vim +778 drivers/block/zram/zram_drv.c

   774	
   775	static void zram_sync_read(struct work_struct *work)
   776	{
   777		struct zram_work *zw = container_of(work, struct zram_work, work);
 > 778		struct bio_bvec bv;
   779		struct bio bio;
   780	
   781		bio_init(&bio, zw->zram->bdev, &bv, 1, REQ_OP_READ);
   782		bio.bi_iter.bi_sector = zw->entry * (PAGE_SIZE >> 9);
   783		__bio_add_page(&bio, zw->page, PAGE_SIZE, 0);
   784		submit_bio_wait(&bio);
   785	}
   786	

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

Re: [PATCH 15/16] zram: fix synchronous reads

[Christoph Hellwig]

Meh, turns out this doesn't even compile for PAGE_SIZE > 4096.

Below is the fix, which also removes the #if and instead relies
on compiler dead code elimination.  I wonder if zram should (maybe
optionally) also offer a 512 byte block size, so that we could
also test the smaller than page size I/O path even on x86.

---
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3af04684c11ebb..c989907301d06e 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -764,7 +764,6 @@ static ssize_t writeback_store(struct device *dev,
 	return ret;
 }
 
-#if PAGE_SIZE != 4096
 struct zram_work {
 	struct work_struct work;
 	struct zram *zram;
@@ -776,7 +775,7 @@ struct zram_work {
 static void zram_sync_read(struct work_struct *work)
 {
 	struct zram_work *zw = container_of(work, struct zram_work, work);
-	struct bio_bvec bv;
+	struct bio_vec bv;
 	struct bio bio;
 
 	bio_init(&bio, zw->zram->bdev, &bv, 1, REQ_OP_READ);
@@ -795,6 +794,9 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 {
 	struct zram_work work;
 
+	if (WARN_ON_ONCE(PAGE_SIZE != 4096))
+		return -EIO;
+
 	work.page = page;
 	work.zram = zram;
 	work.entry = entry;
@@ -806,14 +808,6 @@ static int read_from_bdev_sync(struct zram *zram, struct page *page,
 
 	return work.error;
 }
-#else
-static int read_from_bdev_sync(struct zram *zram, struct page *page,
-				unsigned long entry)
-{
-	WARN_ON(1);
-	return -EIO;
-}
-#endif
 
 static int read_from_bdev(struct zram *zram, struct page *page,
 			unsigned long entry, struct bio *parent)

Re: [PATCH 15/16] zram: fix synchronous reads

[Minchan Kim]

On Fri, Apr 07, 2023 at 06:37:43AM +0200, Christoph Hellwig wrote:
> On Thu, Apr 06, 2023 at 05:23:51PM -0700, Minchan Kim wrote:
> > rw_page path so that bio comes next to serve the rw_page failure.
> > In the case, zram will always do chained bio so we are fine with
> > asynchronous IO.
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index b8549c61ff2c..23fa0e03cdc1 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -1264,6 +1264,8 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
> >                 struct bio_vec bvec;
> > 
> >                 zram_slot_unlock(zram, index);
> > +               if (partial_io)
> > +                       return -EAGAIN;
> > 
> >                 bvec.bv_page = page;
> >                 bvec.bv_len = PAGE_SIZE;
> 
> What tree is this supposed to apply to?  6.2 already has the
> zram_bvec_read_from_bdev helper.

It was for prior to 6.1 where doesn't have (94541bc3fbde4, zram: always
expose rw_page). Since 6.1, with returning -EOPNOTSUPP on the rw_page,
it will defer the request to be handled via submit_bio so every IO to
read data from backing device will have parent bio and chained.

> 
> 
> But either way partial_io can be true when called from zram_bvec_write,
> where we can't just -EAGAIN as ->submit_bio is not allowed to return
> that except for REQ_NOWAIT bios, and even then it needs to be handle
> them when submitted without REQ_NOWAIT.

The case returning -EAGAIN is only rw_page path not the submit_bio path
so the request will be deferred to submit_bio path. However, yeah,
I see it's still broken since read_from_bdev_sync never wait the read
complettion again.

Then, as you suggested, just disable the feature for non-4K would be
the simple option.

I see only this way to achieve it and not sure it will cover all the
cases. If you have better idea, let me know.

Thank you!

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 0386b7da02aa..ae7662430789 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -58,6 +58,12 @@ config ZRAM_DEF_COMP
 config ZRAM_WRITEBACK
        bool "Write back incompressible or idle page to backing device"
        depends on ZRAM
+       depends on !PAGE_SIZE_8KB
+       depends on !PAGE_SIZE_16KB
+       depends on !PAGE_SIZE_32KB
+       depends on !PAGE_SIZE_64KB
+       depends on !PAGE_SIZE_256KB
+       depends on !PAGE_SIZE_1MB
        help
         With incompressible page, there is no memory saving to keep it
         in memory. Instead, write it out to backing device.

Re: [PATCH 15/16] zram: fix synchronous reads

[kernel test robot]

Hi Christoph,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe-block/for-next]
[also build test ERROR on linus/master v6.3-rc5 next-20230406]
[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/Christoph-Hellwig/zram-make-zram_bio_discard-more-self-contained/20230406-234133
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/20230406144102.149231-16-hch%40lst.de
patch subject: [PATCH 15/16] zram: fix synchronous reads
config: ia64-allyesconfig (https://download.01.org/0day-ci/archive/20230408/202304081219.Y5WyFKHp-lkp@intel.com/config)
compiler: ia64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/e4596d7c2cf157f5b3d566cb2cc0769c9232a728
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Christoph-Hellwig/zram-make-zram_bio_discard-more-self-contained/20230406-234133
        git checkout e4596d7c2cf157f5b3d566cb2cc0769c9232a728
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=ia64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=ia64 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304081219.Y5WyFKHp-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/block/zram/zram_drv.c: In function 'zram_sync_read':
>> drivers/block/zram/zram_drv.c:778:25: error: storage size of 'bv' isn't known
     778 |         struct bio_bvec bv;
         |                         ^~
   drivers/block/zram/zram_drv.c:778:25: warning: unused variable 'bv' [-Wunused-variable]


vim +778 drivers/block/zram/zram_drv.c

   774	
   775	static void zram_sync_read(struct work_struct *work)
   776	{
   777		struct zram_work *zw = container_of(work, struct zram_work, work);
 > 778		struct bio_bvec bv;
   779		struct bio bio;
   780	
   781		bio_init(&bio, zw->zram->bdev, &bv, 1, REQ_OP_READ);
   782		bio.bi_iter.bi_sector = zw->entry * (PAGE_SIZE >> 9);
   783		__bio_add_page(&bio, zw->page, PAGE_SIZE, 0);
   784		submit_bio_wait(&bio);
   785	}
   786	

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