[stgt] [PATCH] tgtd: refresh ready fds of event loop after event deletion

[Hitoshi Mitake]

At Mon, 17 Feb 2014 17:12:18 +0900,
Hitoshi Mitake wrote:
> 
> Current main event loop (event_loop()) of tgtd has a possibility of
> segmentation fault. The problem is caused by the below sequence:
> 
> 1. Event A, B are ready so epoll_wait(2) returns.
> 2. The handler of the event A is called. In the event handler, the
>    event B is deleted with tgt_event_del()
> 3. event_loop() tries to call the handler of the event B. It causes
>    segfault because the event struct is already removed and freed.
> 
> For avoid this problem, this patch adds a new global variable
> event_need_refresh. If the value of this variable is 1, event_loop()
> calls epoll_wait(2) again for refreshing ready fd list. This patch
> also lets tgt_event_del() to turn on the flag in its tail. With this
> modification, the above segfault is avoided.
> 
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> ---
>  usr/tgtd.c |   10 ++++++++++
>  usr/tgtd.h |    2 ++
>  2 files changed, 12 insertions(+)

I found a little problem in this patch. I'll send v2 soon.

Thanks,
Hitoshi

> 
> diff --git a/usr/tgtd.c b/usr/tgtd.c
> index 09c1442..c758458 100644
> --- a/usr/tgtd.c
> +++ b/usr/tgtd.c
> @@ -215,6 +215,8 @@ static struct event_data *tgt_event_lookup(int fd)
>  	return NULL;
>  }
>  
> +int event_need_refresh;
> +
>  void tgt_event_del(int fd)
>  {
>  	struct event_data *tev;
> @@ -232,6 +234,8 @@ void tgt_event_del(int fd)
>  
>  	list_del(&tev->e_list);
>  	free(tev);
> +
> +	event_need_refresh = 1;
>  }
>  
>  int tgt_event_modify(int fd, int events)
> @@ -419,6 +423,7 @@ retry:
>  	sched_remains = tgt_exec_scheduled();
>  	timeout = sched_remains ? 0 : -1;
>  
> +refresh:
>  	nevent = epoll_wait(ep_fd, events, ARRAY_SIZE(events), timeout);
>  	if (nevent < 0) {
>  		if (errno != EINTR) {
> @@ -429,6 +434,11 @@ retry:
>  		for (i = 0; i < nevent; i++) {
>  			tev = (struct event_data *) events[i].data.ptr;
>  			tev->handler(tev->fd, events[i].events, tev->data);
> +
> +			if (event_need_refresh) {
> +				event_need_refresh = 0;
> +				goto refresh;
> +			}
>  		}
>  	}
>  
> diff --git a/usr/tgtd.h b/usr/tgtd.h
> index a708f13..91dd7b4 100644
> --- a/usr/tgtd.h
> +++ b/usr/tgtd.h
> @@ -406,4 +406,6 @@ struct service_action *
>  find_service_action(struct service_action *service_action,
>  		    uint32_t action);
>  
> +extern int event_need_refresh;
> +
>  #endif
> -- 
> 1.7.10.4
> 
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