Messages in this thread | | | Subject | Re: strange crashes in tcp_poll() via epoll_wait | From | Eric Dumazet <> | Date | Fri, 19 Jul 2013 17:10:05 -0700 |
| |
On Fri, 2013-07-19 at 23:50 +0000, Eric Wong wrote: > Eric Dumazet <eric.dumazet@gmail.com> wrote: > > Hi Al > > > > I tried to debug strange crashes in tcp_poll() called from > > sys_epoll_wait() -> sock_poll() > > > > The symptom is that sock->sk is NULL and we therefore dereference a NULL > > pointer. > > > > It's really rare crashes but still, it would be nice to understand where > > is the bug. Presumably latest kernels would crash in sock_poll() because > > of the sk_can_busy_loop(sock->sk) call. > > > > We do test sock->sk being NULL in sock_fasync(), but epoll should be > > safe because of existing synchronization (epmutex) ? > > It should be safe because of ep->mtx, actually, as epmutex is not taken > in sys_epoll_wait.
Hmm, it might be more complex than that for multi threaded programs :
eventpoll_release_file()
The problem might be because a thread closes a socket while an event was queued for it.
> > I took a look at this but have not found anything. I've yet to see this > this on my machines. > > When did you start noticing this?
Hard to say, but we have these crashes on a 3.3+ based kernel.
Probability of said crashes is very very low.
| |