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.

Link: https://lkml.kernel.org/r/20210312173949.2197662-1-minchan@kernel.org
Fixes: 3b82a051c101("drivers/block/zram/zram_drv.c: fix error return codes not being returned in writeback_store")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Colin Ian King <colin.king@canonical.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>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a711a2e2a7946bc466913c38585b867b62151748..63bbefdffc818b40cbfd1c4a1335d3b1967782de 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -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;
                }