Date: Mon, 5 Sep 2016 09:53:03 +0200 From: Hans Petter Selasky <hps@selasky.org> To: Andriy Voskoboinyk <avos@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Hans Petter Selasky <hps@freebsd.org> Cc: "freebsd-wireless@freebsd.org" <freebsd-wireless@freebsd.org>, "freebsd-usb@freebsd.org" <freebsd-usb@freebsd.org> Subject: Re: Deadlock between device_detach() and usbd_do_request_flags() Message-ID: <4cf378ff-63e1-7cdc-6120-9578fceec20d@selasky.org> In-Reply-To: <op.ynaawb2n4dikkl@localhost> References: <op.ynaawb2n4dikkl@localhost>
next in thread | previous in thread | raw e-mail | index | archive | help
On 09/04/16 23:20, Andriy Voskoboinyk wrote: > There is a rare, but reproducible deadlock for wlan(4) drivers: > > Thread 1: > * uhub_explore_handle_re_enumerate() (obtains enum_sx lock) > * usbd_set_config_index() > * usb_unconfigure() > * usb_detach_device() > * usb_detach_device_sub() > * <device_detach()> > typically <device_stop()> is executed here (prevents > another possible deadlock?) > * ieee80211_ifdetach() > * ieee80211_vap_destroy() > * <ic->ic_vap_delete> > * ieee80211_vap_detach() > here it calls ieee80211_stop() and waits for <any> -> INIT state > transition > > Thread 2 (started from thread 1): > * ieee80211_newstate_cb() > * vap->iv_newstate() > here: if the driver will try to call usbd_do_request_flags() > (typically via <drv_write_reg> / <drv_read_reg>) it will hang > (because enum_sx lock is already held by thread 1). > > > Another way: execute some periodical task that will try to access > some registers (urtwn_temp_calib(), rum_ratectl_task(), > run_ratectl_cb()) while thread 1 is running - deadlock is > here too, since <device_detach> will wait for them indefinitely > (via ieee80211_draintask()) > > Right now the most obvious (and, probably, wrong) way is to just > detect & release all locks (usbd_enum_unlock()) for > ieee80211_ifdetach() / ieee80211_draintask() and re-acquire them > later (not tested yet). > Hi, I think the right solution is to let usbd_do_request_flags() use its own SX lock for synchronization, instead of re-using the enumeration SX lock. What do you think about that? --HPS
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4cf378ff-63e1-7cdc-6120-9578fceec20d>