On Wed, Jun 17, 2015 at 3:13 AM, Richard Weinberger <richard.weinber...@gmail.com> wrote: > On Wed, Jun 17, 2015 at 11:48 AM, Ingo Molnar <mi...@kernel.org> wrote: >> >> * Andy Lutomirski <l...@kernel.org> wrote: >> >>> This is incomplete, but it's finally good enough that I think it's >>> time to get other opinions on it. It is a complete rewrite of the >>> slow path code that handles exits to user mode. >> >> Modulo the small comments I made about the debug checks interface plus naming >> details the structure and intention of this series gives me warm fuzzy >> feelings. >> >>> The exit-to-usermode code is copied in several places and is written in a >>> nasty >>> combination of asm and C. It's not at all clear what it's supposed to do, >>> and >>> the way it's structured makes it very hard to work with. For example, it's >>> not >>> even clear why syscall exit hooks are called only once per syscall right >>> now. >>> (It seems to be a side effect of the way that rdi and rdx are handled in >>> the asm >>> loop, and it seems reliable, but it's still pointlessly complicated.) The >>> existing code also makes context tracking overly complicated and hard to >>> understand. Finally, it's nearly impossible for anyone to change what >>> happens >>> on exit to usermode, since the existing code is so fragile. >> >> Amen. >> >>> I tried to clean it up incrementally, but I decided it was too hard. >>> Instead, >>> this series just replaces the code. It seems to work. >> >> Any known bugs beyond UML build breakage? >> >>> Context tracking in particular works very differently now. The low-level >>> entry >>> code checks that we're in CONTEXT_USER and switches to CONTEXT_KERNEL. The >>> exit >>> code does the reverse. There is no need to track what CONTEXT_XYZ state we >>> came >>> from, because we already know. Similarly, SCHEDULE_USER is gone, since we >>> can >>> reschedule if needed by simply calling schedule() from C code. >>> >>> The main things that are missing are that I haven't done the 32-bit parts >>> (anyone want to help?) and therefore I haven't deleted the old C code. I >>> also >>> think this may break UML for trivial reasons. >>> >>> Because I haven't converted the 32-bit code yet, all of the now-unnecessary >>> unnecessary calls to exception_enter are still present in traps.c. >>> >>> IRQ context tracking is still duplicated. We should probably clean it up by >>> changing the core code to supply something like >>> irq_enter_we_are_already_in_context_kernel. >>> >>> Thoughts? >> >> So assuming you fix the UML build I'm inclined to go for it, even in this >> incomplete form, to increase testing coverage. > > Andy, can you please share the build breakage you're facing? > I'll happily help you fixing it. >
The do_signal declaration in arch/um/include/shared/kern_util.h conflicts with the one I added to arch/x86/include/asm/signal.h. The latter shouldn't really be included in UML, I think, but I didn't see how to fix it. Just renaming one of the functions would resolve the conflict. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
