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

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Date:   Wed, 28 Dec 2022 15:48:01 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Hannes Reinecke <hare@...e.de>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH] scsi: libfc: Use refcount_* APIs for reference count
 management

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@...lo.com>

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
>