zram: clarify writeback_store() comment

mainline inclusion
from mainline-v6.2-rc1
commit 9fda785d
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7TWVA
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fda785dbd14cfc7d874d00d2b007cb143aa48d0

-------------------------------------------

Re-phrase writeback BIO error comment.

Link: https://lkml.kernel.org/r/20221109115047.2921851-7-senozhatsky@chromium.orgReported-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NSergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: NMinchan Kim <minchan@kernel.org>
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJinjiang Tu <tujinjiang@huawei.com>

drivers/block/zram/zram_drv.c

@@ -751,8 +751,12 @@ static ssize_t writeback_store(struct device *dev,
 			zram_clear_flag(zram, index, ZRAM_IDLE);
 			zram_slot_unlock(zram, index);
 			/*
-			 * Return last IO error unless every IO were
-			 * not suceeded.
+			 * BIO errors are not fatal, we continue and simply
+			 * attempt to writeback the remaining objects (pages).
+			 * At the same time we need to signal user-space that
+			 * some writes (at least one, but also could be all of
+			 * them) were not successful and we do so by returning
+			 * the most recent BIO error.
 			 */
 			ret = err;
 			continue;