Hi Haijun, * haijun liu <liuhaijun.er@xxxxxxxxx> [2010-11-01 09:22:14 +0800]: > Hi Gustavo, > > >> >> >> During test session with another vendor's bt stack, found that in > >> >> >> l2cap_chan_del() using del_timer() caused l2cap_monitor_timeout() > >> >> >> be called after the sock was freed, so it raised a system crash. > >> >> >> So I just replaced del_timer() with del_timer_sync() to solve it. > >> >> > > >> >> > NAK on this. If you read the del_timer_sync() documentation you can > >> >> > see that you can't call del_timer_sync() on interrupt context. The > >> >> > possible solution here is to check in the beginning of > >> >> > l2cap_monitor_timeout() if your sock is still valid. > >> >> > > >> >> > >> >> You are right, I only considered close() interface, so missed the interrupt > >> >> context. > >> >> > >> >> It's very difficult to check sock valid or not in timeout procedure, since it's > >> >> an interrupt context, and only can get context from parameter pre-stored, > >> >> except global variables. > >> > > >> > I think you can check for sk == null there. > >> > > >> > >> It's a pre-stored parameter, it will not change by itself. > > > > I looked a bit into this and a good solution seems to be to hold a > > reference to the sock when we call a mod_timer() and then put the > > reference when we call del_timer() and the timer is inactive or when > > l2cap_monitor_timeout(). Look net/sctp/ for examples. > > > > Same situation still is there, in this case, l2cap_monitor_timeout() > how to know the reference has been released by del_timer()? > > If we refer to net/sctp, use timer_pending() to detect it, unless we can > ensure del_timer() always be called in interrupt context and same > level compare to timer interrupt, otherwise it's not an atomic operation > for this case. No, the socket lock take care of that, so there will be no race condition here. One related thing that we should fix is a locking problem in l2cap_monitor_timeout() and l2cap_retrans_timeout() already reported by Mat Martineau. (I just can't find his e-mail about that). So I think you should go ahead and this problem using ref counting and then we can also fix the problem reported by Mat. -- Gustavo F. Padovan ProFUSION embedded systems - http://profusion.mobi -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
