linux-kernel - [PATCH] zram: rely on the bi_end_io for zram_rw

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Date:	Fri, 14 Nov 2014 09:49:07 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Minchan Kim <minchan@...nel.org>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Karam Lee <karam.lee@....com>,
	Dave Chinner <david@...morbit.com>
Subject: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails

When I tested zram, I found processes got segfaulted.
The reason was zram_rw_page doesn't make the page dirty
again when swap write failed, and even it doesn't return
error by [1].

If error by zram internal happens, zram_rw_page should return
non-zero without calling page_endio.
It causes resubmit the IO with bio so that it ends up calling
bio->bi_end_io.

The reason is zram could be used for a block device for FS and
swap, which they uses different bio complete callback, which
works differently. So, we should rely on the bio I/O complete
handler rather than zram_bvec_rw itself in case of I/O fail.

This patch fixes the segfault issue as well one [1]'s
mentioned

[1] zram: make rw_page opeartion return 0

Cc: Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc: Karam Lee <karam.lee@....com>
Cc: Dave Chinner <david@...morbit.com>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 drivers/block/zram/zram_drv.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 4b4f4dbc3cfd..0e0650feab2a 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -978,12 +978,10 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 out_unlock:
 	up_read(&zram->init_lock);
 out:
-	page_endio(page, rw, err);
+	if (unlikely(err))
+		return err;
 
-	/*
-	 * Return 0 prevents I/O fallback trial caused by rw_page fail
-	 * and upper layer can handle this IO error via page error.
-	 */
+	page_endio(page, rw, 0);
 	return 0;
 }
 
-- 
2.0.0

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