| Message ID | 20220620222032.3839547-3-paulmck@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 5288720dd61c8706aa7159ef20697dcad0ba2567 |
| Headers | show |
| Series | Miscellaneous fixes for v5.20 | expand |
On 6/21/2022 3:50 AM, Paul E. McKenney wrote: > From: Zqiang <qiang1.zhang@intel.com> > > Currently, the rcu_node structure's ->cbovlmask field is set in call_rcu() > when a given CPU is suffering from callback overload. But if that CPU > goes offline, the outgoing CPU's callbacks is migrated to the running > CPU, which is likely to overload the running CPU. However, that CPU's > bit in its leaf rcu_node structure's ->cbovlmask field remains zero. > > Initially, this is OK because the outgoing CPU's bit remains set. > However, that bit will be cleared at the next end of a grace period, > at which time it is quite possible that the running CPU will still > be overloaded. If the running CPU invokes call_rcu(), then overload > will be checked for and the bit will be set. Except that there is no > guarantee that the running CPU will invoke call_rcu(), in which case the > next grace period will fail to take the running CPU's overload condition > into account. Plus, because the bit is not set, the end of the grace > period won't check for overload on this CPU. > > This commit therefore adds a call to check_cb_ovld_locked() in > check_cb_ovld_locked() to set the running CPU's ->cbovlmask bit Nit: s/check_cb_ovld_locked/rcutree_migrate_callbacks/ > appropriately. > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > --- Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com> Thanks Neeraj > kernel/rcu/tree.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index c19d5926886fb..f4a37f2032664 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -4491,6 +4491,7 @@ void rcutree_migrate_callbacks(int cpu) > needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp); > rcu_segcblist_disable(&rdp->cblist); > WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); > + check_cb_ovld_locked(my_rdp, my_rnp); > if (rcu_rdp_is_offloaded(my_rdp)) { > raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ > __call_rcu_nocb_wake(my_rdp, true, flags);
On Tue, Jun 21, 2022 at 11:27:28AM +0530, Neeraj Upadhyay wrote: > > > On 6/21/2022 3:50 AM, Paul E. McKenney wrote: > > From: Zqiang <qiang1.zhang@intel.com> > > > > Currently, the rcu_node structure's ->cbovlmask field is set in call_rcu() > > when a given CPU is suffering from callback overload. But if that CPU > > goes offline, the outgoing CPU's callbacks is migrated to the running > > CPU, which is likely to overload the running CPU. However, that CPU's > > bit in its leaf rcu_node structure's ->cbovlmask field remains zero. > > > > Initially, this is OK because the outgoing CPU's bit remains set. > > However, that bit will be cleared at the next end of a grace period, > > at which time it is quite possible that the running CPU will still > > be overloaded. If the running CPU invokes call_rcu(), then overload > > will be checked for and the bit will be set. Except that there is no > > guarantee that the running CPU will invoke call_rcu(), in which case the > > next grace period will fail to take the running CPU's overload condition > > into account. Plus, because the bit is not set, the end of the grace > > period won't check for overload on this CPU. > > > > This commit therefore adds a call to check_cb_ovld_locked() in > > check_cb_ovld_locked() to set the running CPU's ->cbovlmask bit > > Nit: s/check_cb_ovld_locked/rcutree_migrate_callbacks/ Good catch, fixed! > > appropriately. > > > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > > --- > > Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com> Thank you, applied. Thanx, Paul > Thanks > Neeraj > > > kernel/rcu/tree.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index c19d5926886fb..f4a37f2032664 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -4491,6 +4491,7 @@ void rcutree_migrate_callbacks(int cpu) > > needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp); > > rcu_segcblist_disable(&rdp->cblist); > > WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); > > + check_cb_ovld_locked(my_rdp, my_rnp); > > if (rcu_rdp_is_offloaded(my_rdp)) { > > raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ > > __call_rcu_nocb_wake(my_rdp, true, flags);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c19d5926886fb..f4a37f2032664 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4491,6 +4491,7 @@ void rcutree_migrate_callbacks(int cpu) needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp); rcu_segcblist_disable(&rdp->cblist); WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); + check_cb_ovld_locked(my_rdp, my_rnp); if (rcu_rdp_is_offloaded(my_rdp)) { raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ __call_rcu_nocb_wake(my_rdp, true, flags);