rp2: Support calling pendsv_suspend/resume from core 1.

Previously, this was subject to races incrementing/decrementing
the counter variable pendsv_lock.

Technically, all that's needed here would be to make pendsv_lock an atomic
counter.

This implementation fulfils a stronger guarantee: it also provides mutual
exclusion for the core which calls pendsv_suspend(). This is because the
current use of pendsv_suspend/resume in MicroPython is to ensure exclusive
access to softtimer data structures, and this does require mutual
exclusion.

The conceptually cleaner implementation would split the mutual exclusion
part out into a softtimer-specific spinlock, but this increases the
complexity and doesn't seem like it makes for a better implementation in
the long run.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

0 files changed, 0 insertions, 0 deletions