zram: fix broken page writeback

BugLink: https://bugs.launchpad.net/bugs/1919492
commit 2766f1821600cc7562bae2128ad0b163f744c5d9 upstream.

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 4479011bfc432475fb4a5a7e3b75e86d5a094dfd..37d11103a706df8bd843f8bf3af901c7291825a0 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -639,8 +639,8 @@ 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;
@@ -664,7 +664,7 @@ 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;