>-----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. -- 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
