> It is also not clear to me if disabling pre-emption for the user-space > (albeit for a very tiny time-window) is incorrect and if their side-effects > are known. If otherwise, I think we should choose to operate in pre-empt > safe mode and avoid all costs associated when done without it.
I never really gave much consideration to returning to user mode with preemption disabled. It would not really have occurred to me that was even possible. I can't say it seems to me like it could ever be a very good idea. I find it hard even to start listing the cans of worms that might be opened by that. Perhaps the powerpc maintainers have a clearer picture of it than I do. What does it mean when there is something that prevents it from returning to user mode? i.e., TIF_SIGPENDING or TIF_NEED_RESCHED, or whatever. It could do a lot in the kernel before it gets back to user mode. What if in there somewhere it blocks voluntarily? Similarly, what does it mean if you get to user mode but the single-stepped instruction is a load/store that gets a page fault? What if it blocks in the page fault handler? For that matter, what about a page fault for the kernel-mode case? Perhaps I'm imagining gremlins where there aren't any, but I just cannot really get my head around this "disable preemption while running some unknown instruction that normally runs with preemption enabled" thing--let alone "disable preemption while returning to user mode". Thanks, Roland _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
