On Mon, Jan 13, 2014 at 03:55:27PM -0800, Andrew Morton wrote:
> On Mon, 13 Jan 2014 20:18:56 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> > Dan and Sergey reported that there is a racy between reset and
> > flushing of pending work so that it could make oops by freeing
> > zram->meta in reset while zram_slot_free can access zram->meta
> > if new request is adding during the race window.
> >
> > This patch moves flush after taking init_lock so it prevents
> > new request so that it closes the race.
> >
> > ..
> >
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -553,14 +553,14 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> > size_t index;
> > struct zram_meta *meta;
> >
> > - flush_work(&zram->free_work);
> > -
> > down_write(&zram->init_lock);
> > if (!zram->init_done) {
> > up_write(&zram->init_lock);
> > return;
> > }
> >
> > + flush_work(&zram->free_work);
> > +
> > meta = zram->meta;
> > zram->init_done = 0;
>
> This makes zram.lock nest inside zram.init_lock, which afaict is new
> behaviour.
Originally, it was nested so it's not new. :)
Look at zram_make_request which hold init_lock and then zram_bvec_rw
hold zram->lock.
>
> That all seems OK and logical - has it been well tested with lockdep?
Yeb.
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--
Kind regards,
Minchan Kim
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