Re: [PATCH 4/4] locking/lockdep: Test all incompatible scenario at once in check_irq_usage()

Peter Zijlstra
2019-04-09T13:03:56Z

On Tue, Apr 02, 2019 at 06:02:44PM +0200, Frederic Weisbecker wrote:
> @@ -1988,45 +1961,151 @@ static int exclusive_bit(int new_bit)
> return state | (dir ^ LOCK_USAGE_DIR_MASK);
> }
>
> +static unsigned long exclusive_dir_mask(unsigned long mask)

Would you mind terribly if I call that: invert_dir_mask() ?

> +{
> + unsigned long excl;
> +
> + /* Invert dir */
> + excl = (mask & LOCKF_ENABLED_IRQ_ALL) >> LOCK_USAGE_DIR_MASK;
> + excl |= (mask & LOCKF_USED_IN_IRQ_ALL) << LOCK_USAGE_DIR_MASK;
> +
> + return excl;
> +}
> +
> +static unsigned long exclusive_mask(unsigned long mask)
> +{
> + unsigned long excl = exclusive_dir_mask(mask);
> +
> + /* Strip read */
> + excl |= (excl & LOCKF_IRQ_READ) >> LOCK_USAGE_READ_MASK;
> + excl &= ~LOCKF_IRQ_READ;
> +
> + return excl;
> +}

And I might write a comment to go with those functions; they're too
clever by half. I'm sure I'll have forgotten how they work in a few
months time.

Very well done :-)

> +/*
> + * Find the first pair of bit match between an original
> + * usage mask and an exclusive usage mask.
> + */
> +static int find_exclusive_match(unsigned long mask,
> + unsigned long excl_mask,
> + enum lock_usage_bit *bit,
> + enum lock_usage_bit *excl_bit)
> +{
> + int fs, nr = 0;
> +
> + while ((fs = ffs(mask))) {
> + int excl;
> +
> + nr += fs;
> + excl = exclusive_bit(nr - 1);
> + if (excl_mask & lock_flag(excl)) {
> + *bit = nr - 1;
> + *excl_bit = excl;
> + return 0;
> + }
> + mask >>= fs - 1;
> + /*
> + * Prevent from shifts of sizeof(long) which can
> + * give unpredictable results.
> + */
> + mask >>= 1;
> + }
> + return -1;

Should we write that like:

for_each_set_bit(bit, &mask, LOCK_USED) {
int excl = exclusive_bit(bit);
if (excl_mask & lock_flag(excl)) {
*bitp = bit;
*excl_bitp = excl;
return 0;
}
}
return -1;

Or something along those lines?

> +}
> +