On Thu, 23 Apr 2020, Oliver Neukum wrote: > Am Donnerstag, den 23.04.2020, 00:10 -0500 schrieb Pete Zaitcev: > > > > I do not agree with this kind of workaround. The model we're following > > is for usb_kill_urb() to cancel the transfer. The usblp invokes it > > through usb_kill_anchored_urbs() and usblp_unlink_urbs(), as seen > > above. There can be no timer hitting anything once it returns. > > Right. It seems to me that the problem is not killing an existing > transfer but a failure to check in case of new transfers whether > the device has been disconnected. > > > 1104 is kzalloc for struct usblp. > > > > > > Freed by task 12266: > > > > save_stack+0x1b/0x80 mm/kasan/common.c:72 > > > > set_track mm/kasan/common.c:80 [inline] > > > > kasan_set_free_info mm/kasan/common.c:337 [inline] > > > > __kasan_slab_free+0x117/0x160 mm/kasan/common.c:476 > > > > slab_free_hook mm/slub.c:1444 [inline] > > > > slab_free_freelist_hook mm/slub.c:1477 [inline] > > > > slab_free mm/slub.c:3034 [inline] > > > > kfree+0xd5/0x300 mm/slub.c:3995 > > > > usblp_disconnect.cold+0x24/0x29 drivers/usb/class/usblp.c:1380 > > > > usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:436 > > > > __device_release_driver drivers/base/dd.c:1137 [inline] > > > > device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1168 > > > > bus_remove_device+0x2eb/0x5a0 drivers/base/bus.c:533 > > > > 1380 is an inlined call to usblp_cleanup, which is just > > a bunch of kfree. > > But that must never happen while while the device is open. > If that ever happens something is wrong with usblp->used. > > > The bug report is still a bug report, but I'm pretty sure the > > culprit is the emulated HCD and/or the gadget layer. Unfortunately, > > I'm not up to speed in that subsystem. Maybe Alan can look at it? > > I doubt it. Operation by a timer triggering a timeout must work. The timer is not the issue. usb_kill_anchored_urbs() waits until all the URBs have completed, and those completions happen when the timer fires. The only suspicious thing I see is that usblp_resume() calls handle_bidir() without first acquiring any mutex. But resume shouldn't race with disconnect. The only other place where read URBs get submitted is under usblp_read(), which does acquire the mutex and checks for disconnection while holding it. So I'm baffled. Alan Stern
