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zram: fix return value on writeback_store

PATCH Applied Minchan Kim 1 participant 2 messages Mar 12, 2021

Subsystems (3)
Stable branch Block layer zram
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Minchan Kim

author maintainer
#0 lore raw

PATCH 1/2 zram: fix return value on writeback_store

writeback_store's return value is overwritten by submit_bio_wait's return value. Thus, writeback_store will return zero since there was no IO error. In the end, write syscall from userspace will see the zero as return value, which could make the process stall to keep trying the write until it will succeed.

Cc Sergey Senozhatsky <[email protected]>
Cc Colin Ian King <[email protected]>
Cc [email protected]
Fixes 3b82a051c101("drivers/block/zram/zram_drv.c: fix error return codes not being returned in writeback_store")
Signed-off-by Minchan Kim <[email protected]>
---
 drivers/block/zram/zram_drv.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
drivers/block/zram/zram_drv.c +8 -3
index a711a2e2a794..63bbefdffc81 100644
@@ -627,7 +627,7 @@ static ssize_t writeback_store(struct device *dev,
 	struct bio_vec bio_vec;
 	struct page *page;
 	ssize_t ret = len;
-	int mode;
+	int mode, err;
 	unsigned long blk_idx = 0;
 
 	if (sysfs_streq(buf, "idle"))

@@ -728,12 +728,17 @@ static ssize_t writeback_store(struct device *dev,
 		 * XXX: A single page IO would be inefficient for write
 		 * but it would be not bad as starter.
 		 */
-		ret = submit_bio_wait(&bio);
-		if (ret) {
+		err = submit_bio_wait(&bio);
+		if (err) {
 			zram_slot_lock(zram, index);
 			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
 			zram_clear_flag(zram, index, ZRAM_IDLE);
 			zram_slot_unlock(zram, index);
+			/*
+			 * Return last IO error unless every IO were
+			 * not suceeded.
+			 */
+			ret = err;
 			continue;
 		}
Signature · 1 line
2.31.0.rc2.261.g7f71774620-goog
author maintainer
#1 lore raw

PATCH 2/2 zram: fix broken page writeback

commit 0d8359620d9b ("zram: support page writeback") introduced two problems. It overwrites writeback_store's return value as kstrtol's return value, which makes return value zero so user could see zero as return value of write syscall even though it wrote data successfully.

It also breaks index value in the loop in that it doesn't increase the index any longer. It means it can write only first starting block index so user couldn't write all idle pages in the zram so lose memory saving chance.

This patch fixes those issues.

Cc Sergey Senozhatsky <[email protected]>
Cc [email protected]
Reported-by Amos Bianchi <[email protected]>
Fixes 0d8359620d9b("zram: support page writeback")
Signed-off-by Minchan Kim <[email protected]>
---
 drivers/block/zram/zram_drv.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
drivers/block/zram/zram_drv.c +3 -3
index 63bbefdffc81..cf8deecc39ef 100644
@@ -638,8 +638,8 @@ static ssize_t writeback_store(struct device *dev,
 		if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
 			return -EINVAL;
 
-		ret = kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index);
-		if (ret || index >= nr_pages)
+		if (kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index) ||
+				index >= nr_pages)
 			return -EINVAL;
 
 		nr_pages = 1;

@@ -663,7 +663,7 @@ static ssize_t writeback_store(struct device *dev,
 		goto release_init_lock;
 	}
 
-	while (nr_pages--) {
+	for (; nr_pages != 0; index++, nr_pages--) {
 		struct bio_vec bvec;
 
 		bvec.bv_page = page;
Signature · 1 line
2.31.0.rc2.261.g7f71774620-goog