On Tue, Jan 29, 2013 at 09:11:08AM +0200, Pekka Enberg wrote:
> On Tue, Jan 29, 2013 at 1:21 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > How about this?
> > ------------------------- >8 -------------------------------
> >
> > From 9f8756ae0b0f2819f93cb94dcd38da372843aa12 Mon Sep 17 00:00:00 2001
> > From: Minchan Kim <minchan@xxxxxxxxxx>
> > Date: Mon, 21 Jan 2013 13:58:52 +0900
> > Subject: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial read/write
> >
> > Now zram allocates new page with GFP_KERNEL in zram I/O path
> > if IO is partial. Unfortunately, It may cause deadlock with
> > reclaim path like below.
> >
> > write_page from fs
> > fs_lock
> > allocation(GFP_KERNEL)
> > reclaim
> > pageout
> > write_page from fs
> > fs_lock <-- deadlock
> >
> > This patch fixes it by using GFP_ATOMIC and GFP_NOIO.
> > In read path, we called kmap_atomic so that we need GFP_ATOMIC
> > while we need GFP_NOIO in write path.
>
> The patch description makes sense now. Thanks!
>
> On Tue, Jan 29, 2013 at 1:21 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> > some modification related to buffer allocation in case of partial IO.
> > But it needs more churn and prevent merge this patch into stable
> > if we should send this to stable so I'd like to keep it as simple
> > as possbile. GFP_IO usage could be separate patch after we merge it.
>
> I don't see why something like below couldn't be merged for stable.
> Going for GFP_ATOMIC might seem like the simplest thing to go for but
> usually bites you in the end.
Looks good to me. I will resend it.
Thanks, Pekka.
>
> Pekka
>
> ------------------------- >8 -------------------------------
>
> >From 936a12b423c58542628d6fd683e859f752eb3d41 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@xxxxxxxxxx>
> Date: Mon, 21 Jan 2013 13:58:52 +0900
> Subject: [PATCH] zram: Fix deadlock bug in partial read/write
>
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cause deadlock with
> reclaim path like below.
>
> write_page from fs
> fs_lock
> allocation(GFP_KERNEL)
> reclaim
> pageout
> write_page from fs
> fs_lock <-- deadlock
>
> This patch fixes it by using GFP_NOIO. In read path, we
> reorganize code flow so that kmap_atomic is called after the
> GFP_NOIO allocation.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Jerome Marchand <jmarchan@xxxxxxxxxx>
> Acked-by: Nitin Gupta <ngupta@xxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> [ penberg@xxxxxxxxxx: don't use GFP_ATOMIC ]
> Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxx>
> ---
> drivers/staging/zram/zram_drv.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index f2a73bd..071e058 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -228,11 +228,12 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> return 0;
> }
>
> - user_mem = kmap_atomic(page);
> if (is_partial_io(bvec))
> /* Use a temporary buffer to decompress the page */
> - uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> - else
> + uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> +
> + user_mem = kmap_atomic(page);
> + if (!is_partial_io(bvec))
> uncmem = user_mem;
>
> if (!uncmem) {
> @@ -279,7 +280,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> * This is a partial IO. We need to read the full page
> * before to write the changes.
> */
> - uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> if (!uncmem) {
> pr_info("Error allocating temp memory!\n");
> ret = -ENOMEM;
> --
> 1.7.11.7
>
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--
Kind regards,
Minchan Kim
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