On Fri, Apr 24, 2015 at 12:25 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Fri, Apr 24, 2015 at 5:00 AM, Brian Gerst <brge...@gmail.com> wrote: >> >> So actually this isn't a preemption issue, as the NULL SS is coming >> from an interrupt from userspace (timer tick, etc.). > > It *is* a preemption issue, in the sense that the interrupt that > clears SS also then returns to user space using an "iret" that will > properly restore it. > > So the only case we need to worry about is the preemption case, where > the interrupt has caused a task switch (typically because it woke > something up or it was the timer interrupt and the timeslice of the > previous task is up), and we switch to another context that returns to > user space using "sysret" instead.
To clarify, I was thinking of the CONFIG_PREEMPT case. A nested interrupt wouldn't change SS, and IST interrupts can't schedule. -- Brian Gerst -- 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/
