--- /dev/null
+From d4edc5b6c480a0917e61d93d55531d7efa6230be Mon Sep 17 00:00:00 2001
+From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
+Date: Mon, 30 Dec 2013 17:05:34 +0530
+Subject: powerpc: Fix the setup of CPU-to-Node mappings during CPU online
+
+From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
+
+commit d4edc5b6c480a0917e61d93d55531d7efa6230be upstream.
+
+On POWER platforms, the hypervisor can notify the guest kernel about dynamic
+changes in the cpu-numa associativity (VPHN topology update). Hence the
+cpu-to-node mappings that we got from the firmware during boot, may no longer
+be valid after such updates. This is handled using the arch_update_cpu_topology()
+hook in the scheduler, and the sched-domains are rebuilt according to the new
+mappings.
+
+But unfortunately, at the moment, CPU hotplug ignores these updated mappings
+and instead queries the firmware for the cpu-to-numa relationships and uses
+them during CPU online. So the kernel can end up assigning wrong NUMA nodes
+to CPUs during subsequent CPU hotplug online operations (after booting).
+
+Further, a particularly problematic scenario can result from this bug:
+On POWER platforms, the SMT mode can be switched between 1, 2, 4 (and even 8)
+threads per core. The switch to Single-Threaded (ST) mode is performed by
+offlining all except the first CPU thread in each core. Switching back to
+SMT mode involves onlining those other threads back, in each core.
+
+Now consider this scenario:
+
+1. During boot, the kernel gets the cpu-to-node mappings from the firmware
+ and assigns the CPUs to NUMA nodes appropriately, during CPU online.
+
+2. Later on, the hypervisor updates the cpu-to-node mappings dynamically and
+ communicates this update to the kernel. The kernel in turn updates its
+ cpu-to-node associations and rebuilds its sched domains. Everything is
+ fine so far.
+
+3. Now, the user switches the machine from SMT to ST mode (say, by running
+ ppc64_cpu --smt=1). This involves offlining all except 1 thread in each
+ core.
+
+4. The user then tries to switch back from ST to SMT mode (say, by running
+ ppc64_cpu --smt=4), and this involves onlining those threads back. Since
+ CPU hotplug ignores the new mappings, it queries the firmware and tries to
+ associate the newly onlined sibling threads to the old NUMA nodes. This
+ results in sibling threads within the same core getting associated with
+ different NUMA nodes, which is incorrect.
+
+ The scheduler's build-sched-domains code gets thoroughly confused with this
+ and enters an infinite loop and causes soft-lockups, as explained in detail
+ in commit 3be7db6ab (powerpc: VPHN topology change updates all siblings).
+
+So to fix this, use the numa_cpu_lookup_table to remember the updated
+cpu-to-node mappings, and use them during CPU hotplug online operations.
+Further, we also need to ensure that all threads in a core are assigned to a
+common NUMA node, irrespective of whether all those threads were online during
+the topology update. To achieve this, we take care not to use cpu_sibling_mask()
+since it is not hotplug invariant. Instead, we use cpu_first_sibling_thread()
+and set up the mappings manually using the 'threads_per_core' value for that
+particular platform. This helps us ensure that we don't hit this bug with any
+combination of CPU hotplug and SMT mode switching.
+
+Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
+Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ arch/powerpc/include/asm/topology.h | 10 ++++-
+ arch/powerpc/mm/numa.c | 70 ++++++++++++++++++++++++++++++++++--
+ 2 files changed, 76 insertions(+), 4 deletions(-)
+
+--- a/arch/powerpc/include/asm/topology.h
++++ b/arch/powerpc/include/asm/topology.h
+@@ -22,7 +22,15 @@ struct device_node;
+
+ static inline int cpu_to_node(int cpu)
+ {
+- return numa_cpu_lookup_table[cpu];
++ int nid;
++
++ nid = numa_cpu_lookup_table[cpu];
++
++ /*
++ * During early boot, the numa-cpu lookup table might not have been
++ * setup for all CPUs yet. In such cases, default to node 0.
++ */
++ return (nid < 0) ? 0 : nid;
+ }
+
+ #define parent_node(node) (node)
+--- a/arch/powerpc/mm/numa.c
++++ b/arch/powerpc/mm/numa.c
+@@ -31,6 +31,8 @@
+ #include <asm/sparsemem.h>
+ #include <asm/prom.h>
+ #include <asm/smp.h>
++#include <asm/cputhreads.h>
++#include <asm/topology.h>
+ #include <asm/firmware.h>
+ #include <asm/paca.h>
+ #include <asm/hvcall.h>
+@@ -152,9 +154,22 @@ static void __init get_node_active_regio
+ }
+ }
+
+-static void map_cpu_to_node(int cpu, int node)
++static void reset_numa_cpu_lookup_table(void)
++{
++ unsigned int cpu;
++
++ for_each_possible_cpu(cpu)
++ numa_cpu_lookup_table[cpu] = -1;
++}
++
++static void update_numa_cpu_lookup_table(unsigned int cpu, int node)
+ {
+ numa_cpu_lookup_table[cpu] = node;
++}
++
++static void map_cpu_to_node(int cpu, int node)
++{
++ update_numa_cpu_lookup_table(cpu, node);
+
+ dbg("adding cpu %d to node %d\n", cpu, node);
+
+@@ -522,11 +537,24 @@ static int of_drconf_to_nid_single(struc
+ */
+ static int numa_setup_cpu(unsigned long lcpu)
+ {
+- int nid = 0;
+- struct device_node *cpu = of_get_cpu_node(lcpu, NULL);
++ int nid;
++ struct device_node *cpu;
++
++ /*
++ * If a valid cpu-to-node mapping is already available, use it
++ * directly instead of querying the firmware, since it represents
++ * the most recent mapping notified to us by the platform (eg: VPHN).
++ */
++ if ((nid = numa_cpu_lookup_table[lcpu]) >= 0) {
++ map_cpu_to_node(lcpu, nid);
++ return nid;
++ }
++
++ cpu = of_get_cpu_node(lcpu, NULL);
+
+ if (!cpu) {
+ WARN_ON(1);
++ nid = 0;
+ goto out;
+ }
+
+@@ -1068,6 +1096,7 @@ void __init do_init_bootmem(void)
+ */
+ setup_node_to_cpumask_map();
+
++ reset_numa_cpu_lookup_table();
+ register_cpu_notifier(&ppc64_numa_nb);
+ cpu_numa_callback(&ppc64_numa_nb, CPU_UP_PREPARE,
+ (void *)(unsigned long)boot_cpuid);
+@@ -1446,6 +1475,33 @@ static int update_cpu_topology(void *dat
+ return 0;
+ }
+
++static int update_lookup_table(void *data)
++{
++ struct topology_update_data *update;
++
++ if (!data)
++ return -EINVAL;
++
++ /*
++ * Upon topology update, the numa-cpu lookup table needs to be updated
++ * for all threads in the core, including offline CPUs, to ensure that
++ * future hotplug operations respect the cpu-to-node associativity
++ * properly.
++ */
++ for (update = data; update; update = update->next) {
++ int nid, base, j;
++
++ nid = update->new_nid;
++ base = cpu_first_thread_sibling(update->cpu);
++
++ for (j = 0; j < threads_per_core; j++) {
++ update_numa_cpu_lookup_table(base + j, nid);
++ }
++ }
++
++ return 0;
++}
++
+ /*
+ * 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.
+@@ -1514,6 +1570,14 @@ int arch_update_cpu_topology(void)
+
+ 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],
++ cpumask_of(raw_smp_processor_id()));
++
+ for (ud = &updates[0]; ud; ud = ud->next) {
+ unregister_cpu_under_node(ud->cpu, ud->old_nid);
+ register_cpu_under_node(ud->cpu, ud->new_nid);
--- /dev/null
+From 91b973f90c1220d71923e7efe1e61f5329806380 Mon Sep 17 00:00:00 2001
+From: Paul Mackerras <paulus@samba.org>
+Date: Sat, 18 Jan 2014 21:14:47 +1100
+Subject: powerpc: Make sure "cache" directory is removed when offlining cpu
+
+From: Paul Mackerras <paulus@samba.org>
+
+commit 91b973f90c1220d71923e7efe1e61f5329806380 upstream.
+
+The code in remove_cache_dir() is supposed to remove the "cache"
+subdirectory from the sysfs directory for a CPU when that CPU is
+being offlined. It tries to do this by calling kobject_put() on
+the kobject for the subdirectory. However, the subdirectory only
+gets removed once the last reference goes away, and the reference
+being put here may well not be the last reference. That means
+that the "cache" subdirectory may still exist when the offlining
+operation has finished. If the same CPU subsequently gets onlined,
+the code tries to add a new "cache" subdirectory. If the old
+subdirectory has not yet been removed, we get a WARN_ON in the
+sysfs code, with stack trace, and an error message printed on the
+console. Further, we ultimately end up with an online cpu with no
+"cache" subdirectory.
+
+This fixes it by doing an explicit kobject_del() at the point where
+we want the subdirectory to go away. kobject_del() removes the sysfs
+directory even though the object still exists in memory. The object
+will get freed at some point in the future. A subsequent onlining
+operation can create a new sysfs directory, even if the old object
+still exists in memory, without causing any problems.
+
+Signed-off-by: Paul Mackerras <paulus@samba.org>
+Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ arch/powerpc/kernel/cacheinfo.c | 3 +++
+ 1 file changed, 3 insertions(+)
+
+--- a/arch/powerpc/kernel/cacheinfo.c
++++ b/arch/powerpc/kernel/cacheinfo.c
+@@ -794,6 +794,9 @@ static void remove_cache_dir(struct cach
+ {
+ remove_index_dirs(cache_dir);
+
++ /* Remove cache dir from sysfs */
++ kobject_del(cache_dir->kobj);
++
+ kobject_put(cache_dir->kobj);
+
+ kfree(cache_dir);
projects / thirdparty / kernel / stable-queue.git / commitdiff
