On Fri, 07 Aug 2020 21:23:38 +0200
Peter Zijlstra <[email protected]> wrote:
> Much of the complexity in irqenter_{enter,exit}() is due to #PF being
> the sole exception that can schedule from kernel context.
>
> One additional wrinkle with #PF is that it is non-maskable, it can
> happen _anywhere_. Due to this, and the wonders of tracing, we can get
> the 'normal' NMI nesting vs TRACE_IRQFLAGS:
>
> local_irq_disable()
> raw_local_irq_disable();
> trace_hardirqs_off();
>
> local_irq_enable();
Do you mean to have that ';' there? That is, it the below is called
from local_irq_enable(), right? A ';' means that local_irq_enable()
is completed.
> trace_hardirqs_on();
> <#PF>
> trace_hardirqs_off()
> ...
> if (!regs_irqs_disabled(regs)
regs has it disabled, so this is false, right?
> trace_hardirqs_on();
> </#PF>
I missed the '/' in the above. At first I thought this was another page
fault :-/
> // WHOOPS -- lockdep thinks IRQs are disabled again!
> raw_local_irqs_enable();
>
> Rework irqenter_{enter,exit}() to save/restore the software state.
>
> Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
> ---
> include/linux/entry-common.h | 1
> kernel/entry/common.c | 52
> ++++++++++++++++++++-----------------------
> 2 files changed, 26 insertions(+), 27 deletions(-)
>
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -310,6 +310,7 @@ void irqentry_exit_to_user_mode(struct p
> #ifndef irqentry_state
> typedef struct irqentry_state {
> bool exit_rcu;
> + bool irqs_enabled;
Instead of passing a structure around, should we look at converting
"irqentry_state" into a flags field?
-- Steve
> } irqentry_state_t;
> #endif
>
