On (10/25/14 17:26), Weijie Yang wrote:
> Date: Sat, 25 Oct 2014 17:26:31 +0800
> From: Weijie Yang <weijie.yang@xxxxxxxxxxx>
> To: 'Minchan Kim' <minchan@xxxxxxxxxx>
> Cc: 'Andrew Morton' <akpm@xxxxxxxxxxxxxxxxxxxx>, 'Dan Streetman'
> <ddstreet@xxxxxxxx>, 'Sergey Senozhatsky' <sergey.senozhatsky@xxxxxxxxx>,
> 'Nitin Gupta' <ngupta@xxxxxxxxxx>, 'Linux-MM' <linux-mm@xxxxxxxxx>,
> 'linux-kernel' <linux-kernel@xxxxxxxxxxxxxxx>, 'Weijie Yang'
> <weijie.yang.kh@xxxxxxxxx>
> Subject: [PATCH 2/2] zram: avoid NULL pointer access when reading
> mem_used_total
> X-Mailer: Microsoft Office Outlook 12.0
>
> There is a rare NULL pointer bug in mem_used_total_show() in concurrent
> situation, like this:
> zram is not initialized, process A is a mem_used_total reader which runs
> periodicity, while process B try to init zram.
>
> process A process B
> access meta, get a NULL value
> init zram, done
> init_done() is true
> access meta->mem_pool, get a NULL pointer BUG
>
> This patch fixes this issue.
>
> Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
-ss
> ---
> drivers/block/zram/zram_drv.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 64dd79a..2ffd7d8 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struct device *dev,
> {
> u64 val = 0;
> struct zram *zram = dev_to_zram(dev);
> - struct zram_meta *meta = zram->meta;
>
> down_read(&zram->init_lock);
> - if (init_done(zram))
> + if (init_done(zram)) {
> + struct zram_meta *meta = zram->meta;
> val = zs_get_total_pages(meta->mem_pool);
> + }
> up_read(&zram->init_lock);
>
> return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
> --
> 1.7.0.4
>
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href