[Cluster-devel] [PATCH 02/17] DLM: Eliminate CF_WRITE_PENDING flag

[Steven Whitehouse]

Hi,


On 09/08/17 06:49, tsutomu.owa at toshiba.co.jp wrote:
> From: Bob Peterson <rpeterso at redhat.com>
>
> Before this patch the CF_WRITE_PENDING flag was used to indicate
> when writes to the socket were pending. This caused race conditions
> whereby one process set the bit and another cleared it. Instead,
> we just check to see if there's anything there to be sent. This
> makes the code more intuitive and bullet-proof.
>
> Signed-off-by: Bob Peterson <rpeterso at redhat.com>
> Reviewed-by: Tadashi Miyauchi <miyauchi at toshiba-tops.co.jp>
>
> ---
>   fs/dlm/lowcomms.c | 21 ++++++++-------------
>   1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
> index 41bf93a..a9b2483 100644
> --- a/fs/dlm/lowcomms.c
> +++ b/fs/dlm/lowcomms.c
> @@ -106,7 +106,6 @@ struct connection {
>   	struct mutex sock_mutex;
>   	unsigned long flags;
>   #define CF_READ_PENDING 1
> -#define CF_WRITE_PENDING 2
>   #define CF_INIT_PENDING 4
>   #define CF_IS_OTHERCON 5
>   #define CF_CLOSE 6
> @@ -426,8 +425,7 @@ static void lowcomms_write_space(struct sock *sk)
>   		clear_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags);
>   	}
>   
> -	if (!test_and_set_bit(CF_WRITE_PENDING, &con->flags))
> -		queue_work(send_workqueue, &con->swork);
> +	queue_work(send_workqueue, &con->swork);
>   }
>   
>   static inline void lowcomms_connect_sock(struct connection *con)
> @@ -578,7 +576,6 @@ static void make_sockaddr(struct sockaddr_storage *saddr, uint16_t port,
>   static void close_connection(struct connection *con, bool and_other,
>   			     bool tx, bool rx)
>   {
> -	clear_bit(CF_WRITE_PENDING, &con->flags);
>   	if (tx && cancel_work_sync(&con->swork))
>   		log_print("canceled swork for node %d", con->nodeid);
>   	if (rx && cancel_work_sync(&con->rwork))
> @@ -1077,7 +1074,6 @@ static void sctp_connect_to_sock(struct connection *con)
>   	if (result == 0)
>   		goto out;
>   
> -
>   bind_err:
>   	con->sock = NULL;
>   	sock_release(sock);
> @@ -1102,7 +1098,6 @@ static void sctp_connect_to_sock(struct connection *con)
>   
>   out:
>   	mutex_unlock(&con->sock_mutex);
> -	set_bit(CF_WRITE_PENDING, &con->flags);
>   }
>   
>   /* Connect a new socket to its peer */
> @@ -1196,7 +1191,6 @@ static void tcp_connect_to_sock(struct connection *con)
>   	}
>   out:
>   	mutex_unlock(&con->sock_mutex);
> -	set_bit(CF_WRITE_PENDING, &con->flags);
>   	return;
>   }
>   
> @@ -1452,9 +1446,7 @@ void dlm_lowcomms_commit_buffer(void *mh)
>   	e->len = e->end - e->offset;
>   	spin_unlock(&con->writequeue_lock);
>   
> -	if (!test_and_set_bit(CF_WRITE_PENDING, &con->flags)) {
> -		queue_work(send_workqueue, &con->swork);
> -	}
> +	queue_work(send_workqueue, &con->swork);
>   	return;
>   
>   out:
> @@ -1524,12 +1516,15 @@ static void send_to_sock(struct connection *con)
>   send_error:
>   	mutex_unlock(&con->sock_mutex);
>   	close_connection(con, false, false, true);
> -	lowcomms_connect_sock(con);
> +	/* Requeue the send work. When the work daemon runs again, it will try
> +	   a new connection, then call this function again. */
> +	queue_work(send_workqueue, &con->swork);
>   	return;
>   
>   out_connect:
>   	mutex_unlock(&con->sock_mutex);
> -	lowcomms_connect_sock(con);
> +	cond_resched();
> +	queue_work(send_workqueue, &con->swork);
I think it would make more sense to call cond_resched() after the  
queue_work() since we want the queued work to run soon after it has been  
queued I think,

Steve.

>   }
>   
>   static void clean_one_writequeue(struct connection *con)
> @@ -1591,7 +1586,7 @@ static void process_send_sockets(struct work_struct *work)
>   
>   	if (con->sock == NULL) /* not mutex protected so check it inside too */
>   		con->connect_action(con);
> -	if (test_and_clear_bit(CF_WRITE_PENDING, &con->flags))
> +	if (!list_empty(&con->writequeue))
>   		send_to_sock(con);
>   }
>