Re: [PATCH] semaphore: use raw_spin_lock_irq instead of raw_spin_lock_irqsave

Ingo Molnar
2018-06-21T14:03:06Z

* Ingo Molnar <mingo@kernel.org> wrote:

>
> * Mikulas Patocka <mpatocka@redhat.com> wrote:
>
> > The sleeping functions down, down_interruptible, down_killable and
> > down_timeout can't be called with interrupts disabled, so we don't have to
> > save and restore interrupt flag.
> >
> > This patch avoids the costly pushf and popf instructions on the semaphore
> > path.
> >
> > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> >
> > ---
> > kernel/locking/semaphore.c | 21 ++++++++-------------
> > 1 file changed, 8 insertions(+), 13 deletions(-)
>
> I've applied this to the locking tree, I suspect we can do this on the condition
> that it doesn't explode in early boot code (which has irqs disabled) and doesn't
> generate early boot lockdep splats either.

Hm, this blew up pretty quick on a pretty regular x86-64 PC white-box, during
early bootup:

PANIC: early exception 0x08 IP 246:10 error ffffffff811537b2 cr2 0xffff88000240cff8

and I think it's due to your patch - verifying that now.

Thanks,

Ingo