zram: identify asynchronous IO's return value

For upcoming asynchronous IO like writeback, zram_rw_page should be
aware of that whether requested IO was completed or submitted
successfully, otherwise error.

For the goal, zram_bvec_rw has three return values.

-errno: returns error number
     0: IO request is done synchronously
     1: IO request is issued successfully.

Link: http://lkml.kernel.org/r/1498459987-24562-7-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Juneho Choi <juno.choi@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 8 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index fcdbbb1e7745..8975f75f113d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -772,7 +772,7 @@ out:
 
 static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
 {
-        int ret;
+        int ret = 0;
         unsigned long alloced_pages;
         unsigned long handle = 0;
         unsigned int comp_len = 0;
@@ -877,7 +877,7 @@ out:
 
         /* Update stats */
         atomic64_inc(&zram->stats.pages_stored);
-        return 0;
+        return ret;
 }
 
 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
@@ -959,6 +959,11 @@ static void zram_bio_discard(struct zram *zram, u32 index,
         }
 }
 
+/*
+ * Returns errno if it has some problem. Otherwise return 0 or 1.
+ * Returns 0 if IO request was done synchronously
+ * Returns 1 if IO request was successfully submitted.
+ */
 static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
                         int offset, bool is_write)
 {
@@ -980,7 +985,7 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 
         generic_end_io_acct(rw_acct, &zram->disk->part0, start_time);
 
-        if (unlikely(ret)) {
+        if (unlikely(ret < 0)) {
                 if (!is_write)
                         atomic64_inc(&zram->stats.failed_reads);
                 else
@@ -1073,7 +1078,7 @@ static void zram_slot_free_notify(struct block_device *bdev,
 static int zram_rw_page(struct block_device *bdev, sector_t sector,
                        struct page *page, bool is_write)
 {
-        int offset, err = -EIO;
+        int offset, ret;
         u32 index;
         struct zram *zram;
         struct bio_vec bv;
@@ -1082,7 +1087,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 
         if (!valid_io_request(zram, sector, PAGE_SIZE)) {
                 atomic64_inc(&zram->stats.invalid_io);
-                err = -EINVAL;
+                ret = -EINVAL;
                 goto out;
         }
 
@@ -1093,7 +1098,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
         bv.bv_len = PAGE_SIZE;
         bv.bv_offset = 0;
 
-        err = zram_bvec_rw(zram, &bv, index, offset, is_write);
+        ret = zram_bvec_rw(zram, &bv, index, offset, is_write);
 out:
         /*
          * If I/O fails, just return error(ie, non-zero) without
@@ -1103,9 +1108,20 @@ out:
          * bio->bi_end_io does things to handle the error
          * (e.g., SetPageError, set_page_dirty and extra works).
          */
-        if (err == 0)
+        if (unlikely(ret < 0))
+                return ret;
+
+        switch (ret) {
+        case 0:
                 page_endio(page, is_write, 0);
-        return err;
+                break;
+        case 1:
+                ret = 0;
+                break;
+        default:
+                WARN_ON(1);
+        }
+        return ret;
 }
 
 static void zram_reset_device(struct zram *zram)