netdev - Re: [PATCH net] sctp: disable BH in sctp_for_each

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Date:   Sat, 10 Jun 2017 12:56:24 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net, Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] sctp: disable BH in sctp_for_each_endpoint

On Sat, Jun 10, 2017 at 02:48:14PM +0800, Xin Long wrote:
> Now sctp holds read_lock when foreach sctp_ep_hashtable without disabling
> BH. If CPU schedules to another thread A at this moment, the thread A may
> be trying to hold the write_lock with disabling BH.
> 
> As BH is disabled and CPU cannot schedule back to the thread holding the
> read_lock, while the thread A keeps waiting for the read_lock. A dead
> lock would be triggered by this.
> 
> This patch is to fix this dead lock by calling read_lock_bh instead to
> disable BH when holding the read_lock in sctp_for_each_endpoint.
> 
> Fixes: 626d16f50f39 ("sctp: export some apis or variables for sctp_diag and reuse some for proc")
> Reported-by: Xiumei Mu <xmu@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Similar is done for proc interface already (sctp_eps_seq_show).

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

> ---
>  net/sctp/socket.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index f16c8d9..30aa0a5 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -4622,13 +4622,13 @@ int sctp_for_each_endpoint(int (*cb)(struct sctp_endpoint *, void *),
>  
>  	for (head = sctp_ep_hashtable; hash < sctp_ep_hashsize;
>  	     hash++, head++) {
> -		read_lock(&head->lock);
> +		read_lock_bh(&head->lock);
>  		sctp_for_each_hentry(epb, &head->chain) {
>  			err = cb(sctp_ep(epb), p);
>  			if (err)
>  				break;
>  		}
> -		read_unlock(&head->lock);
> +		read_unlock_bh(&head->lock);
>  	}
>  
>  	return err;
> -- 
> 2.1.0
> 
> --
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