linux-kernel - Re: [PATCH net 1/3] net/smc: Resolve the race between link group access and termination

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Message-ID: <8b720956-c8fe-0fe2-b019-70518d5c60c8@linux.ibm.com>
Date:   Tue, 11 Jan 2022 09:23:08 +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 1/3] net/smc: Resolve the race between link group
 access and termination

On 10/01/2022 10:26, Wen Gu wrote:
> We encountered some crashes caused by the race between the access
> and the termination of link groups.
> 

>  
> +/* won't be freed until no one accesses to lgr anymore */
> +static void __smc_lgr_free(struct smc_link_group *lgr)
> +{
> +	smc_lgr_free_bufs(lgr);
> +	if (!lgr->is_smcd)
> +		smc_wr_free_lgr_mem(lgr);
> +	kfree(lgr);
> +}
> +
>  /* remove a link group */
>  static void smc_lgr_free(struct smc_link_group *lgr)
>  {
> @@ -1298,7 +1326,6 @@ static void smc_lgr_free(struct smc_link_group *lgr)
>  		smc_llc_lgr_clear(lgr);
>  	}
>  
> -	smc_lgr_free_bufs(lgr);
>  	destroy_workqueue(lgr->tx_wq);
>  	if (lgr->is_smcd) {
>  		smc_ism_put_vlan(lgr->smcd, lgr->vlan_id);
> @@ -1306,11 +1333,21 @@ static void smc_lgr_free(struct smc_link_group *lgr)
>  		if (!atomic_dec_return(&lgr->smcd->lgr_cnt))
>  			wake_up(&lgr->smcd->lgrs_deleted);
>  	} else {
> -		smc_wr_free_lgr_mem(lgr);
>  		if (!atomic_dec_return(&lgr_cnt))
>  			wake_up(&lgrs_deleted);

These waiters (seaparate ones for smcd and smcr) are used to wait for all lgrs 
to be deleted when a module unload or reboot was triggered, so it must only be 
woken up when the lgr is actually freed.