powerpc: Only obtain cpu_hotplug_lock if called by rtasd
Calling arch_update_cpu_topology from a CPU hotplug state machine callback
hits a deadlock because the function tries to get a read lock on
cpu_hotplug_lock while the state machine still holds a write lock on it.
Since all callers of arch_update_cpu_topology except rtasd already hold
cpu_hotplug_lock, this patch changes the function to use
stop_machine_cpuslocked and creates a separate function for rtasd which
still tries to obtain the lock.
Michael Bringmann investigated the bug and provided a detailed analysis
of the deadlock on this previous RFC for an alternate solution:
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: John Allen <jallen@linux.vnet.ibm.com>
Cc: Michael Bringmann <mwb@linux.vnet.ibm.com>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1497996510-4032-1-git-send-email-bauerman@linux.vnet.ibm.com
Link: https://patchwork.ozlabs.org/patch/771293/
diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 8b3b46b..a2d36b7 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -43,6 +43,7 @@
extern int sysfs_add_device_to_node(struct device *dev, int nid);
extern void sysfs_remove_device_from_node(struct device *dev, int nid);
+extern int numa_update_cpu_topology(bool cpus_locked);
#else
@@ -57,6 +58,11 @@
int nid)
{
}
+
+static inline int numa_update_cpu_topology(bool cpus_locked)
+{
+ return 0;
+}
#endif /* CONFIG_NUMA */
#if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c
index 3650732..0f0b1b2 100644
--- a/arch/powerpc/kernel/rtasd.c
+++ b/arch/powerpc/kernel/rtasd.c
@@ -283,7 +283,7 @@
* the RTAS event.
*/
pseries_devicetree_update(-prrn_update_scope);
- arch_update_cpu_topology();
+ numa_update_cpu_topology(false);
}
static DECLARE_WORK(prrn_work, prrn_work_fn);
diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 371792e..b95c584 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1311,8 +1311,10 @@
/*
* Update the node maps and sysfs entries for each cpu whose home node
* has changed. Returns 1 when the topology has changed, and 0 otherwise.
+ *
+ * cpus_locked says whether we already hold cpu_hotplug_lock.
*/
-int arch_update_cpu_topology(void)
+int numa_update_cpu_topology(bool cpus_locked)
{
unsigned int cpu, sibling, changed = 0;
struct topology_update_data *updates, *ud;
@@ -1400,15 +1402,23 @@
if (!cpumask_weight(&updated_cpus))
goto out;
- stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
+ if (cpus_locked)
+ stop_machine_cpuslocked(update_cpu_topology, &updates[0],
+ &updated_cpus);
+ else
+ stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
/*
* Update the numa-cpu lookup table with the new mappings, even for
* offline CPUs. It is best to perform this update from the stop-
* machine context.
*/
- stop_machine(update_lookup_table, &updates[0],
+ if (cpus_locked)
+ stop_machine_cpuslocked(update_lookup_table, &updates[0],
cpumask_of(raw_smp_processor_id()));
+ else
+ stop_machine(update_lookup_table, &updates[0],
+ cpumask_of(raw_smp_processor_id()));
for (ud = &updates[0]; ud; ud = ud->next) {
unregister_cpu_under_node(ud->cpu, ud->old_nid);
@@ -1426,6 +1436,12 @@
return changed;
}
+int arch_update_cpu_topology(void)
+{
+ lockdep_assert_cpus_held();
+ return numa_update_cpu_topology(true);
+}
+
static void topology_work_fn(struct work_struct *work)
{
rebuild_sched_domains();