Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
From: Minchan Kim
Date: Tue Nov 18 2014 - 18:51:37 EST
On Tue, Nov 18, 2014 at 03:23:36PM -0800, Andrew Morton wrote:
> On Fri, 14 Nov 2014 09:49:07 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > 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 .
> > 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 's
> > mentioned
> > ...
> > --- 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;
> Losing the comment makes me sad. The code is somewhat odd-looking. We
> should add some words explaining why we're not reporting errors at this
Okay. How about this?
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index decca6f161b8..1d7c90d5e0d0 100644
@@ -975,6 +975,12 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
err = zram_bvec_rw(zram, &bv, index, offset, rw);
+ * If I/O fails, just return error without calling page_endio.
+ * It causes resubmit the I/O with bio request by rw_page fallback
+ * and bio I/O complete handler does things to handle the error
+ * (e.g., set_page_dirty of swap_writepage fail).
if (err == 0)
page_endio(page, rw, 0);
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