On Mon, 2011-08-22 at 14:24 -0400, Josh Boyer wrote: > Hi All, > > We've gotten a report[1] that the ivtv driver is throwing a lockdep > warning when calling ivtv_gpio_init. From what I can tell, it seems > like the lock being held twice is the one allocated for ivtv->cxhdl, but > I can't immediately see where it's locked and not unlocked in the > callstack path. > > Does anyone have an idea where this could be happening? Yes, I do. Right here: http://git.linuxtv.org/media_tree.git/blob/refs/heads/staging/for_v3.2:/drivers/media/video/v4l2-ctrls.c#l1120 But it is almost certainly a false positive because of the way the mutex is initialized in the body of a helper function used by many drivers: http://git.linuxtv.org/media_tree.git/blob/refs/heads/staging/for_v3.2:/drivers/media/video/v4l2-ctrls.c#l1099 So there is no way for lockdep to distinguish between a control handler lock in the bridge driver vs. one of the subdevices under the bridge driver's control. The mutex should really be initialized in a macro or inline function. Say like in this patch: http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg26097.html http://permalink.gmane.org/gmane.linux.drivers.video-input-infrastructure/27027 See if it still applies and solves your problem. Further reading: Comments 11-13 of this ivtv bugzilla report: https://bugzilla.redhat.com/show_bug.cgi?id=662384 This post by me: http://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg33565.html Honestly I wish all mutexes and spinlocks were initalized with such descriptive names as my patch sets up for the control handler mutex. It would make the output of lockdep a lot easier to follow. Regards, Andy W. > [ 28.556610] ============================================= > [ 28.557007] [ INFO: possible recursive locking detected ] > [ 28.557007] 3.1.0-0.rc0.git19.1.fc17.x86_64 #1 > [ 28.557007] --------------------------------------------- > [ 28.557007] modprobe/684 is trying to acquire lock: > [ 28.557007] (&hdl->lock){+.+...}, at: [<ffffffffa02919ba>] > find_ref_lock+0x24/0x46 [videodev] > [ 28.557007] > [ 28.557007] but task is already holding lock: > [ 28.557007] (&hdl->lock){+.+...}, at: [<ffffffffa029380f>] > v4l2_ctrl_add_handler+0x49/0x97 [videodev] > [ 28.557007] > [ 28.557007] other info that might help us debug this: > [ 28.557007] Possible unsafe locking scenario: > [ 28.557007] > [ 28.557007] CPU0 > [ 28.557007] ---- > [ 28.557007] lock(&hdl->lock); > [ 28.557007] lock(&hdl->lock); > [ 28.557007] > [ 28.557007] *** DEADLOCK *** > [ 28.557007] > [ 28.557007] May be due to missing lock nesting notation > [ 28.557007] > [ 28.557007] 3 locks held by modprobe/684: > [ 28.557007] #0: (&__lockdep_no_validate__){......}, at: > [<ffffffff81314d0c>] __driver_attach+0x3b/0x82 > [ 28.557007] #1: (&__lockdep_no_validate__){......}, at: > [<ffffffff81314d1a>] __driver_attach+0x49/0x82 > [ 28.557007] #2: (&hdl->lock){+.+...}, at: [<ffffffffa029380f>] > v4l2_ctrl_add_handler+0x49/0x97 [videodev] > [ 28.557007] > [ 28.557007] stack backtrace: > [ 28.557007] Pid: 684, comm: modprobe Not tainted > 3.1.0-0.rc0.git19.1.fc17.x86_64 #1 > [ 28.557007] Call Trace: > [ 28.557007] [<ffffffff8108eb06>] __lock_acquire+0x917/0xcf7 > [ 28.557007] [<ffffffff81014fbe>] ? sched_clock+0x9/0xd > [ 28.557007] [<ffffffff8108dffc>] ? mark_lock+0x2d/0x220 > [ 28.557007] [<ffffffffa02919ba>] ? find_ref_lock+0x24/0x46 [videodev] > [ 28.557007] [<ffffffff8108f3dc>] lock_acquire+0xf3/0x13e > [ 28.584886] [<ffffffffa02919ba>] ? find_ref_lock+0x24/0x46 [videodev] > [ 28.585146] [<ffffffffa02919ba>] ? find_ref_lock+0x24/0x46 [videodev] > [ 28.585146] [<ffffffff814f2523>] __mutex_lock_common+0x5d/0x39a > [ 28.585146] [<ffffffffa02919ba>] ? find_ref_lock+0x24/0x46 [videodev] > [ 28.585146] [<ffffffff8108f6db>] ? mark_held_locks+0x6d/0x95 > [ 28.585146] [<ffffffff814f282f>] ? __mutex_lock_common+0x369/0x39a > [ 28.585146] [<ffffffff8108f830>] ? trace_hardirqs_on_caller+0x12d/0x164 > [ 28.585146] [<ffffffff814f296f>] mutex_lock_nested+0x40/0x45 > [ 28.585146] [<ffffffffa02919ba>] find_ref_lock+0x24/0x46 [videodev] > [ 28.585146] [<ffffffffa029367e>] handler_new_ref+0x42/0x18a [videodev] > [ 28.585146] [<ffffffffa0293833>] v4l2_ctrl_add_handler+0x6d/0x97 [videodev] > [ 28.585146] [<ffffffffa028f71b>] v4l2_device_register_subdev+0x16c/0x257 > [videodev] > [ 28.585146] [<ffffffffa02ddfe9>] ivtv_gpio_init+0x14e/0x159 [ivtv] > [ 28.585146] [<ffffffffa02ebd57>] ivtv_probe+0xdc4/0x1662 [ivtv] > [ 28.585146] [<ffffffff8108f6c3>] ? mark_held_locks+0x55/0x95 > [ 28.585146] [<ffffffff814f41df>] ? _raw_spin_unlock_irqrestore+0x4d/0x61 > [ 28.585146] [<ffffffff8126a12b>] local_pci_probe+0x44/0x75 > [ 28.585146] [<ffffffff8126acb1>] pci_device_probe+0xd0/0xff > [ 28.585146] [<ffffffff81314bef>] driver_probe_device+0x131/0x213 > [ 28.585146] [<ffffffff81314d2f>] __driver_attach+0x5e/0x82 > [ 28.585146] [<ffffffff81314cd1>] ? driver_probe_device+0x213/0x213 > [ 28.585146] [<ffffffff81313c30>] bus_for_each_dev+0x59/0x8f > [ 28.585146] [<ffffffff813147c3>] driver_attach+0x1e/0x20 > [ 28.585146] [<ffffffff813143db>] bus_add_driver+0xd4/0x22a > [ 28.585146] [<ffffffffa02ff000>] ? 0xffffffffa02fefff > [ 28.585146] [<ffffffff813151f2>] driver_register+0x98/0x105 > [ 28.618302] [<ffffffffa02ff000>] ? 0xffffffffa02fefff > [ 28.618302] [<ffffffff8126b584>] __pci_register_driver+0x66/0xd2 > [ 28.618302] [<ffffffffa02ff000>] ? 0xffffffffa02fefff > [ 28.618302] [<ffffffffa02ff078>] module_start+0x78/0x1000 [ivtv] > [ 28.618302] [<ffffffff81002099>] do_one_initcall+0x7f/0x13a > [ 28.618302] [<ffffffffa02ff000>] ? 0xffffffffa02fefff > [ 28.618302] [<ffffffff8109a864>] sys_init_module+0x114/0x267 > [ 28.618302] [<ffffffff814fafc2>] system_call_fastpath+0x16/0x1b > > josh > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=728316 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
