Re: [PATCH] scsi: libfc: Use refcount_* APIs for reference count management

From: Deepak R Varma
Date: Wed Dec 28 2022 - 05:18:20 EST


On Tue, Dec 20, 2022 at 10:00:45AM +0530, Deepak R Varma wrote:
> The atomic_t API based object reference counter management is prone to
> counter value overflows, object use-after-free issues and to return
> puzzling values. The improved refcount_t APIs are designed to address
> these known issues with atomic_t reference counter management. This
> white paper [1] has detailed reasons for moving from atomic_t to
> refcount_t APIs. Hence replace the atomic_* based implementation by its
> refcount_* based equivalent.
> The issue is identified using atomic_as_refcounter.cocci Coccinelle
> semantic patch script.
>
> [1] https://arxiv.org/pdf/1710.06175.pdf
>
> Signed-off-by: Deepak R Varma <drv@xxxxxxxxx>

Hello,
May I please request a review and feedback on this patch proposal?

Thank you,
./drv

> ---
> Note: The proposal is compile tested only.
>
> drivers/scsi/libfc/fc_exch.c | 10 +++++-----
> include/scsi/libfc.h | 2 +-
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
> index 1d91c457527f..1c49fddb65e3 100644
> --- a/drivers/scsi/libfc/fc_exch.c
> +++ b/drivers/scsi/libfc/fc_exch.c
> @@ -246,7 +246,7 @@ static const char *fc_exch_rctl_name(unsigned int op)
> */
> static inline void fc_exch_hold(struct fc_exch *ep)
> {
> - atomic_inc(&ep->ex_refcnt);
> + refcount_inc(&ep->ex_refcnt);
> }
>
> /**
> @@ -312,7 +312,7 @@ static void fc_exch_release(struct fc_exch *ep)
> {
> struct fc_exch_mgr *mp;
>
> - if (atomic_dec_and_test(&ep->ex_refcnt)) {
> + if (refcount_dec_and_test(&ep->ex_refcnt)) {
> mp = ep->em;
> if (ep->destructor)
> ep->destructor(&ep->seq, ep->arg);
> @@ -329,7 +329,7 @@ static inline void fc_exch_timer_cancel(struct fc_exch *ep)
> {
> if (cancel_delayed_work(&ep->timeout_work)) {
> FC_EXCH_DBG(ep, "Exchange timer canceled\n");
> - atomic_dec(&ep->ex_refcnt); /* drop hold for timer */
> + refcount_dec(&ep->ex_refcnt); /* drop hold for timer */
> }
> }
>
> @@ -1897,7 +1897,7 @@ static void fc_exch_reset(struct fc_exch *ep)
> ep->state |= FC_EX_RST_CLEANUP;
> fc_exch_timer_cancel(ep);
> if (ep->esb_stat & ESB_ST_REC_QUAL)
> - atomic_dec(&ep->ex_refcnt); /* drop hold for rec_qual */
> + refcount_dec(&ep->ex_refcnt); /* drop hold for rec_qual */
> ep->esb_stat &= ~ESB_ST_REC_QUAL;
> sp = &ep->seq;
> rc = fc_exch_done_locked(ep);
> @@ -2332,7 +2332,7 @@ static void fc_exch_els_rrq(struct fc_frame *fp)
> */
> if (ep->esb_stat & ESB_ST_REC_QUAL) {
> ep->esb_stat &= ~ESB_ST_REC_QUAL;
> - atomic_dec(&ep->ex_refcnt); /* drop hold for rec qual */
> + refcount_dec(&ep->ex_refcnt); /* drop hold for rec qual */
> }
> if (ep->esb_stat & ESB_ST_COMPLETE)
> fc_exch_timer_cancel(ep);
> diff --git a/include/scsi/libfc.h b/include/scsi/libfc.h
> index 6e29e1719db1..ce65149b300c 100644
> --- a/include/scsi/libfc.h
> +++ b/include/scsi/libfc.h
> @@ -432,7 +432,7 @@ struct fc_seq {
> */
> struct fc_exch {
> spinlock_t ex_lock;
> - atomic_t ex_refcnt;
> + refcount_t ex_refcnt;
> enum fc_class class;
> struct fc_exch_mgr *em;
> struct fc_exch_pool *pool;
> --
> 2.34.1
>