On Wed, 26 Feb 2014 14:13:22 +0900
Hitoshi Mitake <mitake.hitoshi@xxxxxxxxxxxxx> 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.
>
> For example, we can produce segfault of tgtd under heavy load. Below
> is a backtrace obtained from the core file:
> (gdb) bt
> #0 0x0000000000000000 in ?? ()
> #1 0x0000000000411419 in event_loop () at tgtd.c:414
> #2 0x0000000000411b65 in main (argc=<value optimized out>, argv=<value optimized out>) at tgtd.c:591
>
> To be honest, I still don't find an event handler which calls
> tgt_event_del() for other fds. But with this modification, the above
> segfault is avoided. The change seems to be effective.
As you pointed out off-line, making a connection closed via tgtadm
might be the case. Anyway, I think that the handler API should allow
removing other handlers from a handler. Merged, thanks a lot!
> +int event_need_refresh;
> +
static?
> void tgt_event_del(int fd)
> {
> struct event_data *tev;
> @@ -229,6 +231,8 @@ 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)
> @@ -426,6 +430,11 @@ 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 retry;
> + }
> }
> }
>
> --
> 1.7.10.4
>
> --
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