[PATCH v2] zram: fix incorrectly stat with failed_reads

[Chao Yu]

Since we allocate a temporary buffer in zram_bvec_read to handle partial page
operations in this commit 924bd88d703e53d30f393fac6117f8f1bc79aab6 (Staging:
zram: allow partial page operations), our ->failed_reads value may be incorrect
as we do not increase its value when failed to allocate the temporary buffer.

Let's fix this issue and correct the annotation of failed_reads.

 v2: clean codes of failed_{reads,writes} stat pointed out by Minchan Kim, and
this cleanup also fix incorrectly stat when fail in zram_decompress_page.

Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 10 +++++++---
 drivers/block/zram/zram_drv.h |  2 +-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index dfa4024..d00831c 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -378,7 +378,6 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 	/* Should NEVER happen. Return bio error if it does. */
 	if (unlikely(ret)) {
 		pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
-		atomic64_inc(&zram->stats.failed_reads);
 		return ret;
 	}
 
@@ -547,8 +546,6 @@ out:
 		zcomp_strm_release(zram->comp, zstrm);
 	if (is_partial_io(bvec))
 		kfree(uncmem);
-	if (ret)
-		atomic64_inc(&zram->stats.failed_writes);
 	return ret;
 }
 
@@ -566,6 +563,13 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
 		ret = zram_bvec_write(zram, bvec, index, offset);
 	}
 
+	if (unlikely(ret)) {
+		if (rw == READ)
+			atomic64_inc(&zram->stats.failed_reads);
+		else
+			atomic64_inc(&zram->stats.failed_writes);
+	}
+
 	return ret;
 }
 
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 5b0afde..e0f725c 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -84,7 +84,7 @@ struct zram_stats {
 	atomic64_t compr_data_size;	/* compressed size of pages stored */
 	atomic64_t num_reads;	/* failed + successful */
 	atomic64_t num_writes;	/* --do-- */
-	atomic64_t failed_reads;	/* should NEVER! happen */
+	atomic64_t failed_reads;	/* can happen when memory is too low */
 	atomic64_t failed_writes;	/* can happen when memory is too low */
 	atomic64_t invalid_io;	/* non-page-aligned I/O requests */
 	atomic64_t notify_free;	/* no. of swap slot free notifications */
-- 
2.0.1.474.g72c7794


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