* [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
@ 2014-11-14 0:49 Minchan Kim
2014-11-15 9:19 ` Sergey Senozhatsky
2014-11-18 23:23 ` Andrew Morton
0 siblings, 2 replies; 6+ messages in thread
From: Minchan Kim @ 2014-11-14 0:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Nitin Gupta, Jerome Marchand, Sergey Senozhatsky, linux-mm,
linux-kernel, Minchan Kim, Matthew Wilcox, Karam Lee,
Dave Chinner
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@intel.com>
Cc: Karam Lee <karam.lee@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Minchan Kim <minchan@kernel.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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^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
2014-11-14 0:49 [PATCH] zram: rely on the bi_end_io for zram_rw_page fails Minchan Kim
@ 2014-11-15 9:19 ` Sergey Senozhatsky
2014-11-18 23:23 ` Andrew Morton
1 sibling, 0 replies; 6+ messages in thread
From: Sergey Senozhatsky @ 2014-11-15 9:19 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, Nitin Gupta, Jerome Marchand, Sergey Senozhatsky,
linux-mm, linux-kernel, Matthew Wilcox, Karam Lee, Dave Chinner
Hi,
On (11/14/14 09:49), Minchan Kim 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 [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@intel.com>
> Cc: Karam Lee <karam.lee@lge.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Minchan Kim <minchan@kernel.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;
this unlikely() case can be turned into a likely() one:
if (err == 0)
page_endio(page, rw, 0);
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;
> }
seems like we also can drop at least one goto (jump-to-return) for
invalid request.
(not sure about `goto out_unblock', yet another up_read(&zram->init_lock)
just will make function bigger).
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
drivers/block/zram/zram_drv.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0e0650f..decca6f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -956,8 +956,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
zram = bdev->bd_disk->private_data;
if (!valid_io_request(zram, sector, PAGE_SIZE)) {
atomic64_inc(&zram->stats.invalid_io);
- err = -EINVAL;
- goto out;
+ return -EINVAL;
}
down_read(&zram->init_lock);
@@ -974,15 +973,11 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
bv.bv_offset = 0;
err = zram_bvec_rw(zram, &bv, index, offset, rw);
-
out_unlock:
up_read(&zram->init_lock);
-out:
- if (unlikely(err))
- return err;
-
- page_endio(page, rw, 0);
- return 0;
+ if (err == 0)
+ page_endio(page, rw, 0);
+ return err;
}
static const struct block_device_operations zram_devops = {
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^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
2014-11-14 0:49 [PATCH] zram: rely on the bi_end_io for zram_rw_page fails Minchan Kim
2014-11-15 9:19 ` Sergey Senozhatsky
@ 2014-11-18 23:23 ` Andrew Morton
2014-11-18 23:52 ` Minchan Kim
1 sibling, 1 reply; 6+ messages in thread
From: Andrew Morton @ 2014-11-18 23:23 UTC (permalink / raw)
To: Minchan Kim
Cc: Nitin Gupta, Jerome Marchand, Sergey Senozhatsky, linux-mm,
linux-kernel, Matthew Wilcox, Karam Lee, Dave Chinner
On Fri, 14 Nov 2014 09:49:07 +0900 Minchan Kim <minchan@kernel.org> 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 [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
>
> ...
>
> --- 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
point.
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
2014-11-18 23:23 ` Andrew Morton
@ 2014-11-18 23:52 ` Minchan Kim
2014-11-19 21:15 ` Andrew Morton
0 siblings, 1 reply; 6+ messages in thread
From: Minchan Kim @ 2014-11-18 23:52 UTC (permalink / raw)
To: Andrew Morton
Cc: Nitin Gupta, Jerome Marchand, Sergey Senozhatsky, linux-mm,
linux-kernel, Matthew Wilcox, Karam Lee, Dave Chinner
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@kernel.org> 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 [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
> >
> > ...
> >
> > --- 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
> point.
Okay. How about this?
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index decca6f161b8..1d7c90d5e0d0 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -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);
out_unlock:
up_read(&zram->init_lock);
+ /*
+ * 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);
return err;
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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--
Kind regards,
Minchan Kim
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^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
2014-11-18 23:52 ` Minchan Kim
@ 2014-11-19 21:15 ` Andrew Morton
2014-11-19 23:32 ` Minchan Kim
0 siblings, 1 reply; 6+ messages in thread
From: Andrew Morton @ 2014-11-19 21:15 UTC (permalink / raw)
To: Minchan Kim
Cc: Nitin Gupta, Jerome Marchand, Sergey Senozhatsky, linux-mm,
linux-kernel, Matthew Wilcox, Karam Lee, Dave Chinner
On Wed, 19 Nov 2014 08:52:01 +0900 Minchan Kim <minchan@kernel.org> wrote:
> > >
> > > - /*
> > > - * 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
> > point.
>
> Okay. How about this?
>
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index decca6f161b8..1d7c90d5e0d0 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -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);
> out_unlock:
> up_read(&zram->init_lock);
> + /*
> + * 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);
> return err;
I don't understand the comment :( bdev_read_page() doesn't resubmit the
IO if block_device_operations.rw_page() returns zero and it's unclear
how the bio I/O complete handler (which one?) gets involved.
It would help in the comment was more specific. Instead of using vague
terms like "rw_page fallback" and "bio I/O complete handler", use
actual function names so the reader understand exactly what code we're
referring to.
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] zram: rely on the bi_end_io for zram_rw_page fails
2014-11-19 21:15 ` Andrew Morton
@ 2014-11-19 23:32 ` Minchan Kim
0 siblings, 0 replies; 6+ messages in thread
From: Minchan Kim @ 2014-11-19 23:32 UTC (permalink / raw)
To: Andrew Morton
Cc: Nitin Gupta, Jerome Marchand, Sergey Senozhatsky, linux-mm,
linux-kernel, Matthew Wilcox, Karam Lee, Dave Chinner
Hello,
On Wed, Nov 19, 2014 at 01:15:35PM -0800, Andrew Morton wrote:
> On Wed, 19 Nov 2014 08:52:01 +0900 Minchan Kim <minchan@kernel.org> wrote:
>
> > > >
> > > > - /*
> > > > - * 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
> > > point.
> >
> > Okay. How about this?
> >
> >
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index decca6f161b8..1d7c90d5e0d0 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -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);
> > out_unlock:
> > up_read(&zram->init_lock);
> > + /*
> > + * 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);
> > return err;
>
> I don't understand the comment :( bdev_read_page() doesn't resubmit the
> IO if block_device_operations.rw_page() returns zero and it's unclear
It's not bdev_read_page but upper functions.
(ie, do_mpage_readpage, swap_readpage, __mpage_writepage, __swap_writepage)
> how the bio I/O complete handler (which one?) gets involved.
bio->bi_end_io.
>
> It would help in the comment was more specific. Instead of using vague
> terms like "rw_page fallback" and "bio I/O complete handler", use
> actual function names so the reader understand exactly what code we're
> referring to.
Indeed. I was terrible.
Hope this is better.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2014-11-14 0:49 [PATCH] zram: rely on the bi_end_io for zram_rw_page fails Minchan Kim
2014-11-15 9:19 ` Sergey Senozhatsky
2014-11-18 23:23 ` Andrew Morton
2014-11-18 23:52 ` Minchan Kim
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