[PATCH net] sctp: disable BH in sctp_for_each_endpoint

[PATCH net] sctp: disable BH in sctp_for_each_endpoint

[Xin Long]

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@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.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

Re: [PATCH net] sctp: disable BH in sctp_for_each_endpoint

[Marcelo Ricardo Leitner]

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@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Similar is done for proc interface already (sctp_eps_seq_show).

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.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
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [PATCH net] sctp: disable BH in sctp_for_each_endpoint

[David Miller]

From: Xin Long <lucien.xin@gmail.com>
Date: Sat, 10 Jun 2017 14:48:14 +0800

> 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@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Applied and queued up for -stable, thanks.