On Wednesday 20 January 2010, Michal Simek wrote: > Joerg Roedel wrote: > > On Wed, Jan 20, 2010 at 10:53:50AM +0000, Russell King wrote: > >> and ops is NULL, then this code will oops; you will get a full register > >> dump and backtrace. You can use this information along with markup_oops.pl > >> to find out where the problem is. > > > > You can't rely on the oops if the code runs in process context. The > > process may have address 0 mapped which would result in a security hole. > > We had two of these bugs last year. > > That's the same problem which I had some days ago and Microblaze misses > valuable backtrace (because we don't have FP or constant frame size). You can do what x86 does and just print anything in the stack that looks like part of a kernel function. > > But I don't see any point in checking for dma_ops != NULL too. Any > > developer would mention such a bug long before init is started. > > I agree that checking adds extra cycles to every dma-api call. > > I like as wrote Russel to check if ops exists or not. If you are worried about the overhead, you could just add the BUG_ON to the map calls but not to unmap and sync, which are rather unlikely (and incorrect) to be called before a map. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
