+ zram-fix-broken-page-writeback.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: zram: fix broken page writeback
has been added to the -mm tree.  Its filename is
     zram-fix-broken-page-writeback.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/zram-fix-broken-page-writeback.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/zram-fix-broken-page-writeback.patch

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------------------------------------------------------
From: Minchan Kim <minchan@kernel.org>
Subject: 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.

Link: https://lkml.kernel.org/r/20210312173949.2197662-2-minchan@kernel.org
Fixes: 0d8359620d9b("zram: support page writeback")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Amos Bianchi <amosbianchi@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: John Dias <joaodias@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/block/zram/zram_drv.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/block/zram/zram_drv.c~zram-fix-broken-page-writeback
+++ a/drivers/block/zram/zram_drv.c
@@ -638,8 +638,8 @@ static ssize_t writeback_store(struct de
 		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 de
 		goto release_init_lock;
 	}
 
-	while (nr_pages--) {
+	for (; nr_pages != 0; index++, nr_pages--) {
 		struct bio_vec bvec;
 
 		bvec.bv_page = page;
_

Patches currently in -mm which might be from minchan@kernel.org are

zram-fix-return-value-on-writeback_store.patch
zram-fix-broken-page-writeback.patch
mm-remove-lru_add_drain_all-in-alloc_contig_range.patch
mm-page_alloc-dump-migrate-failed-pages.patch
mm-vmstat-add-cma-statistics.patch
mm-cma-support-sysfs.patch