On 21/06/18 16:02, Ingo Molnar wrote: > > * Ingo Molnar <[email protected]> wrote: > >> >> * Mikulas Patocka <[email protected]> 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 <[email protected]> >>> >>> --- >>> 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.
I guess local_irq_enable() being called by raw_spin_unlock_irq() makes its usage in early boot code undesirable. Maybe it would be possible to use alternatives for that case? They are applied after enabling interrupts, so pushf and popf instructions could be patched away. Juergen
