On 12/8/2016 4:25 PM, John Stultz wrote: > On Thu, Dec 8, 2016 at 4:17 PM, John Youn <John.Youn@xxxxxxxxxxxx> wrote: >> On 12/8/2016 3:12 PM, John Stultz wrote: >>> Hey John, >>> In my testing I've come across another issue in the dwc2 driver. >>> >>> Basically when plugging in various cables in different orders, I'm >>> occasionally seeing the following BUG splat: >>> >>> [ 86.215403] BUG: scheduling while atomic: kworker/u16:2/53/0x00000002 >>> [ 86.219164] usb 1-1: USB disconnect, device number 9 >>> [ 86.226845] Preemption disabled at:[ 86.230218] >>> [<ffffff8008673558>] dwc2_conn_id_status_change+0x120/0x250 >>> [ 86.236894] CPU: 0 PID: 53 Comm: kworker/u16:2 Tainted: G W >>> 4.9.0-rc8-00051-gd5a7979-dirty #1702 >>> [ 86.246836] Hardware name: HiKey Development Board (DT) >>> [ 86.252100] Workqueue: dwc2 dwc2_conn_id_status_change >>> [ 86.257279] Call trace: >>> [ 86.259771] [<ffffff8008087c28>] dump_backtrace+0x0/0x1a0 >>> [ 86.265210] [<ffffff8008087ddc>] show_stack+0x14/0x20 >>> [ 86.270308] [<ffffff80084343f0>] dump_stack+0x90/0xb0 >>> [ 86.275401] [<ffffff80080d8d94>] __schedule_bug+0x6c/0xb8 >>> [ 86.280841] [<ffffff8008a07220>] __schedule+0x4f8/0x5b0 >>> [ 86.286099] [<ffffff8008a073e8>] schedule+0x38/0xa0 >>> [ 86.291017] [<ffffff8008a0a6cc>] schedule_hrtimeout_range_clock+0x8c/0xf0 >>> [ 86.297846] [<ffffff8008a0a740>] schedule_hrtimeout_range+0x10/0x18 >>> [ 86.304150] [<ffffff8008a0a4a0>] usleep_range+0x50/0x58 >>> [ 86.309418] [<ffffff800866d8dc>] dwc2_wait_for_mode.isra.4+0x54/0xd0 >>> [ 86.315815] [<ffffff800866f058>] dwc2_core_reset+0xe0/0x168 >>> [ 86.321431] [<ffffff800867e364>] dwc2_hsotg_core_init_disconnected+0x2c/0x310 >>> [ 86.328602] [<ffffff8008673568>] dwc2_conn_id_status_change+0x130/0x250 >>> [ 86.335254] [<ffffff80080ccd48>] process_one_work+0x118/0x370 >>> [ 86.341035] [<ffffff80080ccfe8>] worker_thread+0x48/0x498 >>> [ 86.346473] [<ffffff80080d2eb0>] kthread+0xd0/0xe8 >>> [ 86.351299] [<ffffff8008082e80>] ret_from_fork+0x10/0x50 >>> >>> >>> This seems to be caused by the dwc2_wait_for_mode() calling >>> usleep_range() while the hstog->lock spinlock is held, since we take >>> that before calling dwc2_hsotg_core_init_disconnected(). >>> >>> I'm sort of surprised this hasn't been noticed before, since it seems >>> dwc2_hsotg_core_init_disconnected() is called from a number of places >>> with the spinlock held. >> >> I think it was uncovered by your peculiar ID pin behvaior :) But it >> could happen normally too, so that's good. >> >> dwc2_hsotg_core_init_disconnected() is only called as a B-device, so >> it shouldn't call dwc2_wait_for_mode() from within >> dwc2_core_reset(). The ID-pin must be going to A-device before we >> finish initialization of B-device, so we shouldn't depend on it being >> consistent after we call this. >> >> It should be enough to force dwc2_core_reset() to run atomically > > Sorry, force it to run atomically? As in add an extra argument for > this case, or are you thinking something different? Yes, and drop the wait entirely. > >> whenever we call it from dwc2_hsotg_core_init_disconnected(). If the >> ID pin changes before it finishes it will be handled afterwards. > > So I've been running with a patch that drops the lock around the > core_reset() call, and that seems to be working. Worth sending out for > consideration, or is it just obviously wrong? > That should work too but we know we don't need to wait whenver we call from dwc2_hsotg_core_init_disconnected(). Regards, John -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
