Re: [Xen-devel] [PATCH v3 1/5] xen/spinlocks: in debug builds store cpu holding the lock

[Juergen Gross <jgross@xxxxxxxx>]

On 03.09.19 16:11, Jan Beulich wrote:
> On 29.08.2019 12:18, Juergen Gross wrote:
> > --- a/xen/include/xen/spinlock.h
> > +++ b/xen/include/xen/spinlock.h
> > @@ -6,14 +6,21 @@
> >   #include <asm/types.h>
> >   
> >   #ifndef NDEBUG
> > -struct lock_debug {
> > -    s16 irq_safe; /* +1: IRQ-safe; 0: not IRQ-safe; -1: don't know yet */
> > +union lock_debug {
> > +    uint16_t val;
> > +#define LOCK_DEBUG_INITVAL 0xffff
> > +    struct {
> > +        uint16_t cpu:12;
> I'm afraid I have one more request: The literal 12 in struct spinlock is
> sitting right next to the SPINLOCK_NO_CPU definition, making it pretty
> unlikely that both author and reviewer of a change wouldn't notice one
> getting changed without adjustment to the other. The literal 12 here,
> though, is sufficiently remote to that other place, so there needs to be
> a connection established. Best I can think of right away is to have a
> #define for the 12, move SPINLOCK_NO_CPU's definition next to it, and
> use the new constant in both places.
Can do.

> > +        uint16_t pad:2;
> While at it, would you mind making this an unnamed field?
NP. I guess the "2" should then be replaced to depend on the added
#define above.


Juergen


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