On Tue, Feb 16, 2010 at 07:37:49PM +0100, samu.p.onkalo@xxxxxxxxx wrote: > > > >-----Original Message----- > >From: ext Dmitry Torokhov [mailto:dmitry.torokhov@xxxxxxxxx] > >Sent: 16 February, 2010 19:51 > >To: Onkalo Samu.P (Nokia-D/Tampere) > >Cc: linux-input@xxxxxxxxxxxxxxx > >Subject: Re: [PATCH] input: polldev can cause crash in case of polling > >disabled > > > >Hi Samu, > > > >On Tue, Feb 16, 2010 at 04:44:41PM +0200, Samu Onkalo wrote: > >> If polling is set to disabled value and polled input device > >> is opened and closed several times, address to workqueue will probably > >> change at some point. Since nothing is queued (due to polled disabled > >> state), content of the work struct contains pointer to the old and > >non-existent > >> workqueue. > > > >This I do not quite understand. The work struct as far as I can see does > >not reference workqueue at all. There is a list entry but if we do not > >poll the device that entry should be always detached from any lists. We > >properly initialize WQ entry when we create the device and it shoudl > >remain valid until the device is destroyed. > > 'data' entry contains a pointer to per-cpu-workqueue which in turn contains > the workqueue pointer. This 'data' entry is not ok in case of failure. I can > Collect more data about this. > > > > >> When the device is closed again, cancel_delayed_work_sync > >> goes crazy due to pointer to nonexisting workqueue. > >> > > > >What kind of failure do you see? Is there a stack trace or something? > > Kernel panic while in workqueue handling (paging fault with some crappy address). > > > > >> In case on disabled polling, init work struct to initial value to > >> clean up the old values. > >> > > > >Also, why would not we see the same issue with enabled polling? The > >workqueue is being created and destroyed in this case as well. > > > Queue_delayed_work updates the work struct. Workqueue itself is ok. > > I think that the sequence goes about this way (no other polled devices open): > 1. Polled device is opened with polling enabled > 2. It first creates workqueue and then queue the first polling. Kernels > Workqueue functions updates current workqueue information to the work-struct > 3. polled device is closed > 4. workqueue is destroyed > > 5. polling interval is set to 0 > 6. device is reopened > 7. New workqueue is created > 8. polled device is closed without queueing a work > 9. work struct for polled device contains pointer to the old (created in 2.) wq > 10. cancel_workqueue... can access unallocated memory causing crash. > Ah, I see. In this case I think it should be fixed in workqueue code by clearing work data so it does not point to the [potentially] non-existing workqueue when we cancel or complete work. Oleg, do you agree? -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
