On Fri, Sep 30, 2016 at 01:40:57PM -0400, Brent DeGraaf wrote: > Prior spinlock code solely used load-acquire and store-release > semantics to ensure ordering of the spinlock lock and the area it > protects. However, store-release semantics and ordinary stores do > not protect against accesses to the protected area being observed > prior to the access that locks the lock itself. > > While the load-acquire and store-release ordering is sufficient > when the spinlock routines themselves are strictly used, other > kernel code that references the lock values directly (e.g. lockrefs)
Isn't the problem with lockref the fact that arch_spin_value_unlocked() isn't a load-acquire, and therefore the CPU in question doesn't need to observe the contents of the critical section etc..? That is, wouldn't fixing arch_spin_value_unlocked() by making that an smp_load_acquire() fix things much better? > could observe changes to the area protected by the spinlock prior > to observance of the lock itself being in a locked state, despite > the fact that the spinlock logic itself is correct.
