On Mon, Mar 29, 2021 at 08:01:41PM +0800, Guo Ren wrote:

u32 a = 0x55aa66bb;
u16 *ptr = &a;

CPU0                       CPU1
=========             =========
xchg16(ptr, new)     while(1)
                                    WRITE_ONCE(*(ptr + 1), x);

When we use lr.w/sc.w implement xchg16, it'll cause CPU0 deadlock.

Then I think your LL/SC is broken.

That also means you really don't want to build super complex locking
primitives on top, because that live-lock will percolate through.

Step 1 would be to get your architecute fixed such that it can provide
fwd progress guarantees for LL/SC. Otherwise there's absolutely no point
in building complex systems with it.