On Sat, Jan 19, 2013 at 10:55:29PM +0100, Markus Grabner wrote: > Am Freitag, 18. Januar 2013, 16:57:31 schrieb Greg Kroah-Hartman: > > On Fri, Jan 18, 2013 at 10:52:14PM +0100, Markus Grabner wrote: > > > The function "line6_send_raw_message_async" now has an additional argument > > > "bool copy", which indicates whether the supplied buffer should be copied > > > into a dynamically allocated block of memory. The copy flag is also > > > stored in the "message" struct such that the temporary memory can be > > > freed when appropriate without intervention of the caller. > > > > Why do this? Why not either always copy it, or always not? > Some messages are sent to the device which have no parameters, they are > declared at global scope as constant byte arrays and therefore must be copied > into a dynamically allocated block of memory in order to be sent over the USB > interface. On the other hand, there are messages which do have parameters and > which are composed in dynamically allocated memory and can therefore directly > be sent without copying. Then if you always copy the memory, and "own" it after the call, you should be fine, right? > > What is this fixing? > Two users reported to me independently that the driver doesn't work for them. > I couldn't reproduce the problem since it seems to be triggered by subtle > timing issues in the system, but after some further investigations, the > kfree() of the message buffer immediately after submitting the message for > asynchronous transmission was clearly identified as the reason for the driver > not working. The patch puts the kfree() at the right place and (hopefully) > prevents incorrect use of the new buffer copy feature. The patch is tested by > me and the users who initially reported the bug, and they confirmed that the > issue is fixed for them. > > If anybody has a better idea how to fix this, please go ahead! The patch might > also become obsolete in the future due to refactoring. But currently there is > a bug which prevents some people from using the driver at all, and this should > be fixed soon IMO. I agree, it should be fixed, but having the code always do the copy and manage the memory, and not have the crazy "flag" option, should solve the bug for everyone. thanks, greg k-h _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
