On Thu, Aug 23 2018 at 6:12pm -0400,
Damien Le Moal <Damien.LeMoal@xxxxxxx> wrote:
> John,
>
> On 2018/08/23 10:37, John Pittman wrote:
> > The API surrounding refcount_t should be used in place of atomic_t
> > when variables are being used as reference counters. This API can
> > prevent issues such as counter overflows and use-after-free
> > conditions. Within the dm zoned metadata stack, the atomic_t API
> > is used for mblk->ref and zone->refcount. Change these to use
> > refcount_t, avoiding the issues mentioned.
> >
> > Signed-off-by: John Pittman <jpittman@xxxxxxxxxx>
> > ---
> > drivers/md/dm-zoned-metadata.c | 25 +++++++++++++------------
> > drivers/md/dm-zoned.h | 2 +-
> > 2 files changed, 14 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
> > index 969954915566..92e635749414 100644
> > --- a/drivers/md/dm-zoned-metadata.c
> > +++ b/drivers/md/dm-zoned-metadata.c
> > @@ -99,7 +99,7 @@ struct dmz_mblock {
> > struct rb_node node;
> > struct list_head link;
> > sector_t no;
> > - atomic_t ref;
> > + refcount_t ref;
>
> While reviewing your patch, I realized that this ref is always manipulated under
> the zmd->mblk_lock spinlock. So there is no need for it to be an atomic or a
> refcount. An unsigned int would do as well and be faster. My fault.
>
> I will send a patch to go on top of yours to fix that.
Hi Damien,
Given what you've said I'm not seeing the point in the intermediate
refcount_t conversion.
I'd rather you just send a patch that switches atomic_t to int.
Thanks,
Mike
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