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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> +        uint16_t pad:2;

While at it, would you mind making this an unnamed field?

Jan

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