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Date:   Mon, 19 Jul 2021 09:51:36 -0500
From:   Dimitri Sivanich <sivanich@hpe.com>
To:     Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc:     Dimitri Sivanich <dimitri.sivanich@hpe.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, yuanxzhang@fudan.edu.cn,
        Xin Tan <tanxin.ctf@gmail.com>
Subject: Re: [PATCH] misc: sgi-gru: Convert from atomic_t to refcount_t on
 gru_thread_state->ts_refcnt
Message-ID: <20210719145136.GA4844@hpe.com>
References: <1626517043-42696-1-git-send-email-xiyuyang19@fudan.edu.cn>
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Acked-by: Dimitri Sivanich <sivanich@hpe.com>

On Sat, Jul 17, 2021 at 06:17:22PM +0800, Xiyu Yang wrote:
> refcount_t type and corresponding API can protect refcounters from
> accidental underflow and overflow and further use-after-free situations.
> 
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  drivers/misc/sgi-gru/grumain.c   | 6 +++---
>  drivers/misc/sgi-gru/grutables.h | 3 ++-
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/sgi-gru/grumain.c b/drivers/misc/sgi-gru/grumain.c
> index 40ac59dd018c..9afda47efbf2 100644
> --- a/drivers/misc/sgi-gru/grumain.c
> +++ b/drivers/misc/sgi-gru/grumain.c
> @@ -282,7 +282,7 @@ static void gru_unload_mm_tracker(struct gru_state *gru,
>   */
>  void gts_drop(struct gru_thread_state *gts)
>  {
> -	if (gts && atomic_dec_return(&gts->ts_refcnt) == 0) {
> +	if (gts && refcount_dec_and_test(&gts->ts_refcnt)) {
>  		if (gts->ts_gms)
>  			gru_drop_mmu_notifier(gts->ts_gms);
>  		kfree(gts);
> @@ -323,7 +323,7 @@ struct gru_thread_state *gru_alloc_gts(struct vm_area_struct *vma,
>  
>  	STAT(gts_alloc);
>  	memset(gts, 0, sizeof(struct gru_thread_state)); /* zero out header */
> -	atomic_set(&gts->ts_refcnt, 1);
> +	refcount_set(&gts->ts_refcnt, 1);
>  	mutex_init(&gts->ts_ctxlock);
>  	gts->ts_cbr_au_count = cbr_au_count;
>  	gts->ts_dsr_au_count = dsr_au_count;
> @@ -888,7 +888,7 @@ struct gru_state *gru_assign_gru_context(struct gru_thread_state *gts)
>  		gts->ts_gru = gru;
>  		gts->ts_blade = gru->gs_blade_id;
>  		gts->ts_ctxnum = gru_assign_context_number(gru);
> -		atomic_inc(&gts->ts_refcnt);
> +		refcount_inc(&gts->ts_refcnt);
>  		gru->gs_gts[gts->ts_ctxnum] = gts;
>  		spin_unlock(&gru->gs_lock);
>  
> diff --git a/drivers/misc/sgi-gru/grutables.h b/drivers/misc/sgi-gru/grutables.h
> index 5ce8f3081e96..e4c067c61251 100644
> --- a/drivers/misc/sgi-gru/grutables.h
> +++ b/drivers/misc/sgi-gru/grutables.h
> @@ -129,6 +129,7 @@
>   *
>   */
>  
> +#include <linux/refcount.h>
>  #include <linux/rmap.h>
>  #include <linux/interrupt.h>
>  #include <linux/mutex.h>
> @@ -358,7 +359,7 @@ struct gru_thread_state {
>  						     enabled */
>  	int			ts_ctxnum;	/* context number where the
>  						   context is loaded */
> -	atomic_t		ts_refcnt;	/* reference count GTS */
> +	refcount_t		ts_refcnt;	/* reference count GTS */
>  	unsigned char		ts_dsr_au_count;/* Number of DSR resources
>  						   required for contest */
>  	unsigned char		ts_cbr_au_count;/* Number of CBR resources
> -- 
> 2.7.4