On Wed, Oct 30, 2019 at 11:12:00AM +0100, Miroslav Benes wrote: > On Tue, 29 Oct 2019, Heiko Carstens wrote: > > > On Tue, Oct 29, 2019 at 03:39:01PM +0100, Miroslav Benes wrote: > > > - I tried to use the existing infrastructure as much as possible with > > > one exception. I kept unwind_next_frame_reliable() next to the > > > ordinary unwind_next_frame(). I did not come up with a nice solution > > > how to integrate it. The reliable unwinding is executed on a task > > > stack only, which leads to a nice simplification. My integration > > > attempts only obfuscated the existing unwind_next_frame() which is > > > already not easy to read. Ideas are definitely welcome. > > > > Ah, now I see. So patch 2 seems to be leftover(?). Could you just send > > how the result would look like? > > > > I'd really like to have only one function, since some of the sanity > > checks you added also make sense for what we already have - so code > > would diverge from the beginning. > > Ok, that is understandable. I tried a bit harder and the outcome does not > look as bad as my previous attempts (read, I gave up too early). > > I deliberately split unwind_reliable/!unwind_reliable case in "No > back-chain, look for a pt_regs structure" branch, because the purpose is > different there. In !unwind_reliable case we can continue on a different > stack (if I understood the code correctly when I analyzed it in the past. > I haven't found a good documentation unfortunately :(). While in > unwind_realiable case we just check if there are pt_regs in the right > place on a task stack and stop. If there are not, error out. > > It applies on top of the patch set. Only compile tested though. If it > looks ok-ish to you, I'll work on it. Yes, that looks much better. Note, from a coding style perspective the 80 characters per line limit is _not_ enforced on s390 kernel code; so that might be a possibility to make the code a bit more readable. Also it _might_ make sense to split the function into two or more functions (without duplicating code). Not sure if that would really increase readability though. FWIW, I just applied your first patch, since it makes sense anyway.
