On Thu, Feb 28, 2013 at 3:25 AM, Oleg Nesterov [off-list ref] wrote:

On 02/27, Michel Lespinasse wrote:

quoted

+void lg_rwlock_local_read_lock(struct lgrwlock *lgrw)
+{
+       preempt_disable();
+
+       if (__this_cpu_read(*lgrw->local_refcnt) ||
+           arch_spin_trylock(this_cpu_ptr(lgrw->lglock->lock))) {
+               __this_cpu_inc(*lgrw->local_refcnt);

Please look at __this_cpu_generic_to_op(). You need this_cpu_inc()
to avoid the race with irs. The same for _read_unlock.

Hmmm, I was thinking that this was safe because while interrupts might
modify local_refcnt to acquire a nested read lock, they are expected
to release that lock as well which would set local_refcnt back to its
original value ???

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.