netdev - Re: [PATCH net 3/3] net/smc: Resolve the race between SMC-R link access and clear

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Date:   Tue, 11 Jan 2022 09:40:05 +0100
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Wen Gu <guwen@...ux.alibaba.com>, davem@...emloft.net,
        kuba@...nel.org
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 3/3] net/smc: Resolve the race between SMC-R link
 access and clear

On 10/01/2022 10:26, Wen Gu wrote:
> @@ -1226,15 +1245,23 @@ void smcr_link_clear(struct smc_link *lnk, bool log)
>  	smc_wr_free_link(lnk);
>  	smc_ib_destroy_queue_pair(lnk);
>  	smc_ib_dealloc_protection_domain(lnk);
> -	smc_wr_free_link_mem(lnk);
> -	smc_lgr_put(lnk->lgr); /* lgr_hold in smcr_link_init() */
>  	smc_ibdev_cnt_dec(lnk);
>  	put_device(&lnk->smcibdev->ibdev->dev);
>  	smcibdev = lnk->smcibdev;
> -	memset(lnk, 0, sizeof(struct smc_link));
> -	lnk->state = SMC_LNK_UNUSED;
>  	if (!atomic_dec_return(&smcibdev->lnk_cnt))
>  		wake_up(&smcibdev->lnks_deleted);

Same here, waiter should not be woken up until the link memory is actually freed.

> +	smcr_link_put(lnk); /* theoretically last link_put */
> +}
> +
> +void smcr_link_hold(struct smc_link *lnk)
> +{
> +	refcount_inc(&lnk->refcnt);
> +}
> +
> +void smcr_link_put(struct smc_link *lnk)
> +{
> +	if (refcount_dec_and_test(&lnk->refcnt))
> +		__smcr_link_clear(lnk);
>  }