__zram_bvec_write() overwrites the existing compressed object only when
it successfully compresses a new one. When zram_compress() fails, we
propagate the error, but never touch the old object, so we keep the old
data for that particular page and all reads that could hit that index
later will read stale data. This can cause problems. By example,
- Overwriting a file
over-write block 1 aaa->xxx OK
over-write block 2 bbb->yyy OK
over-write block 3 ccc->zzz error << the block still has 'ccc' data.
- Now, reading the file
read block 1 xxx OK
read block 2 yyy OK
read block 3 ccc OK << we should not return OK here. Because
"xxxyyyccc" is not correct file.
As a solution, when we fail to compress a new page (S/W or H/W compressor
error, depending on particular setup) try to store the page uncompressed
(PAGE_SIZE-ed zs_pool object). This, at least, lets us to return valid
and correct data:
read block 1 xxx - OK, compressed
read block 2 yyy - OK, compressed
read block 3 zzz - OK, uncompressed (because compressing back-end
returned an error)
Signed-off-by: Sergey Senozhatsky <[email protected]>
---
drivers/block/zram/zram_drv.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 372602c7da49..ba3e36bbb619 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -723,10 +723,12 @@ static int zram_compress(struct zram *zram, struct
zcomp_strm **zstrm,
kunmap_atomic(src);
if (unlikely(ret)) {
+ /*
+ * We failed to compress the page, try to store it
+ * uncompressed (if there is enough memory).
+ */
pr_err("Compression failed! err=%d\n", ret);
- if (entry)
- zram_entry_free(zram, entry);
- return ret;
+ comp_len = PAGE_SIZE;
}
if (unlikely(comp_len > max_zpage_size))
--
2.13.0
