* Mathieu Desnoyers wrote:
> Just to let you know that I pushed two updates into urcu: one fixes a
> grace period hang caused by a missing wakeup in the synchronize_rcu
> QSBR code. This appears to hit us due to the more fine-grained wakeup
> code brought by Paolo. The wakeup was really missing from the
> synchronize_rcu code (so Paolo's code just triggered an existing
> problem). I thought it would be good to let you know the effect: grace
> periods are delayed forever. This problem never appeared in a release
> (I caught it before).
Good catch. Why not use rcu_thread_offline/online in synchronize_rcu,
instead of touching rcu_reader.ctr directly? I had this in my QEMU
branch but hadn't posted yet because it was meant as a cleanup only.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
was_online = rcu_reader.ctr;
/* All threads should read qparity before accessing data structure
was_online = rcu_reader.ctr;
/* All threads should read qparity before accessing data structure
- * where new ptr points to.
- */
- /* Write new ptr before changing the qparity */
- cmm_smp_mb();
-
- /*
+ * where new ptr points to. In the "then" case, rcu_thread_offline
+ * includes a memory barrier.
+ *
* Mark the writer thread offline to make sure we don't wait for
* our own quiescent state. This allows using synchronize_rcu()
* in threads registered as readers.
*/
* Mark the writer thread offline to make sure we don't wait for
* our own quiescent state. This allows using synchronize_rcu()
* in threads registered as readers.
*/
- if (was_online) {
- CMM_STORE_SHARED(rcu_reader.ctr, 0);
- cmm_smp_mb(); /* write rcu_reader.ctr before read futex */
- wake_up_gp();
- }
+ if (was_online)
+ rcu_thread_offline();
+ else
+ cmm_smp_mb();
mutex_lock(&rcu_gp_lock);
mutex_lock(&rcu_gp_lock);
* freed.
*/
if (was_online)
* freed.
*/
if (was_online)
- _CMM_STORE_SHARED(rcu_reader.ctr,
- CMM_LOAD_SHARED(rcu_gp_ctr));
- cmm_smp_mb();
+ rcu_thread_online();
+ else
+ cmm_smp_mb();
}
#else /* !(CAA_BITS_PER_LONG < 64) */
void synchronize_rcu(void)
}
#else /* !(CAA_BITS_PER_LONG < 64) */
void synchronize_rcu(void)
* our own quiescent state. This allows using synchronize_rcu()
* in threads registered as readers.
*/
* our own quiescent state. This allows using synchronize_rcu()
* in threads registered as readers.
*/
- cmm_smp_mb();
- if (was_online) {
- CMM_STORE_SHARED(rcu_reader.ctr, 0);
- cmm_smp_mb(); /* write rcu_reader.ctr before read futex */
- wake_up_gp();
- }
+ if (was_online)
+ rcu_thread_offline();
+ else
+ cmm_smp_mb();
mutex_lock(&rcu_gp_lock);
if (cds_list_empty(®istry))
mutex_lock(&rcu_gp_lock);
if (cds_list_empty(®istry))
mutex_unlock(&rcu_gp_lock);
if (was_online)
mutex_unlock(&rcu_gp_lock);
if (was_online)
- _CMM_STORE_SHARED(rcu_reader.ctr,
- CMM_LOAD_SHARED(rcu_gp_ctr));
- cmm_smp_mb();
+ rcu_thread_online();
+ else
+ cmm_smp_mb();
}
#endif /* !(CAA_BITS_PER_LONG < 64) */
}
#endif /* !(CAA_BITS_PER_LONG < 64) */