| Message ID | 20220620224503.3841196-2-paulmck@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 24a57affd242566fef2935f04f062350b8275187 |
| Headers | show |
| Series | Callback-offload (nocb) updates for v5.20 | expand |
On 6/21/2022 4:14 AM, Paul E. McKenney wrote: > From: Zqiang <qiang1.zhang@intel.com> > > In case of failure to spawn either rcuog or rcuo[p] kthreads for a given > rdp, rcu_nocb_rdp_deoffload() needs to be called with the hotplug > lock and the barrier_mutex held. However cpus write lock is already held > while calling rcutree_prepare_cpu(). It's not possible to call > rcu_nocb_rdp_deoffload() from there with just locking the barrier_mutex > or this would result in a locking inversion against > rcu_nocb_cpu_deoffload() which holds both locks in the reverse order. > > Simply solve this with inverting the locking order inside > rcu_nocb_cpu_[de]offload(). This will be a pre-requisite to toggle NOCB > states toward cpusets anyway. > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> > Cc: Boqun Feng <boqun.feng@gmail.com> > Cc: Uladzislau Rezki <uladzislau.rezki@sony.com> > Cc: Joel Fernandes <joel@joelfernandes.org> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > --- Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com> Thanks Neeraj > kernel/rcu/tree_nocb.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index dac74952e1d1b..f2f2cab6285a1 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1055,8 +1055,8 @@ int rcu_nocb_cpu_deoffload(int cpu) > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > int ret = 0; > > - mutex_lock(&rcu_state.barrier_mutex); > cpus_read_lock(); > + mutex_lock(&rcu_state.barrier_mutex); > if (rcu_rdp_is_offloaded(rdp)) { > if (cpu_online(cpu)) { > ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp); > @@ -1067,8 +1067,8 @@ int rcu_nocb_cpu_deoffload(int cpu) > ret = -EINVAL; > } > } > - cpus_read_unlock(); > mutex_unlock(&rcu_state.barrier_mutex); > + cpus_read_unlock(); > > return ret; > } > @@ -1134,8 +1134,8 @@ int rcu_nocb_cpu_offload(int cpu) > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > int ret = 0; > > - mutex_lock(&rcu_state.barrier_mutex); > cpus_read_lock(); > + mutex_lock(&rcu_state.barrier_mutex); > if (!rcu_rdp_is_offloaded(rdp)) { > if (cpu_online(cpu)) { > ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp); > @@ -1146,8 +1146,8 @@ int rcu_nocb_cpu_offload(int cpu) > ret = -EINVAL; > } > } > - cpus_read_unlock(); > mutex_unlock(&rcu_state.barrier_mutex); > + cpus_read_unlock(); > > return ret; > }
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index dac74952e1d1b..f2f2cab6285a1 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1055,8 +1055,8 @@ int rcu_nocb_cpu_deoffload(int cpu) struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); int ret = 0; - mutex_lock(&rcu_state.barrier_mutex); cpus_read_lock(); + mutex_lock(&rcu_state.barrier_mutex); if (rcu_rdp_is_offloaded(rdp)) { if (cpu_online(cpu)) { ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp); @@ -1067,8 +1067,8 @@ int rcu_nocb_cpu_deoffload(int cpu) ret = -EINVAL; } } - cpus_read_unlock(); mutex_unlock(&rcu_state.barrier_mutex); + cpus_read_unlock(); return ret; } @@ -1134,8 +1134,8 @@ int rcu_nocb_cpu_offload(int cpu) struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); int ret = 0; - mutex_lock(&rcu_state.barrier_mutex); cpus_read_lock(); + mutex_lock(&rcu_state.barrier_mutex); if (!rcu_rdp_is_offloaded(rdp)) { if (cpu_online(cpu)) { ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp); @@ -1146,8 +1146,8 @@ int rcu_nocb_cpu_offload(int cpu) ret = -EINVAL; } } - cpus_read_unlock(); mutex_unlock(&rcu_state.barrier_mutex); + cpus_read_unlock(); return ret; }