On Wed, Aug 12, 2015 at 04:38:21PM +0200, Frederic Weisbecker wrote: > On Tue, Aug 11, 2015 at 11:33:12AM -0700, Paul E. McKenney wrote: > > On Tue, Aug 11, 2015 at 10:49:36AM -0700, Andy Lutomirski wrote: > > > Some arches may need: > > > > > > i_am_lame_and_forgot_my_previous_context() > > > > > > x86 will soon (4.3 or 4.4, depending on how my syscall cleanup goes) > > > no longer need that. > > > > > > Paul says that some arches need something that goes straight from IRQ > > > to user mode (?) -- sigh. > > > > Straight from IRQ to process-level kernel mode. I ran into this in > > late 2011, and clearly should have documented exactly what code was > > doing this. Something about invoking system calls from within the > > kernel on some architectures. > > > > Hey, if no architectures do this anymore, I could simplify RCU a bit! ;-) > > That issue has always been a bit foggy to me :-) > > We never really stated what exactly the issue was. Just performing syscalls > from kernel mode shouldn't fiddle with the dynticks count. > > IIUC, the issue was that some IRQs triggered and never returned. But we > certainly can't remove the safety code without clearly identifying the > issue... This was not a theoretical problem -- there were real failures. But yes, the safety code is there and seems to work OK, so I do need confirmation of a change before removing it. I do recall someone arguing that the half-interrupts should go away, but I never did hear that they really did go away. Adding linux-arch in the hope that someone can say for sure. Thanx, Paul -- 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
