Patch "powerpc/numa: Fix percpu allocations to be NUMA aware" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/numa: Fix percpu allocations to be NUMA aware

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-numa-fix-percpu-allocations-to-be-numa-aware.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Michael Ellerman <[email protected]>
Date: Tue, 6 Jun 2017 20:23:57 +1000
Subject: powerpc/numa: Fix percpu allocations to be NUMA aware

From: Michael Ellerman <[email protected]>

commit ba4a648f12f4cd0a8003dd229b6ca8a53348ee4b upstream.

In commit 8c272261194d ("powerpc/numa: Enable USE_PERCPU_NUMA_NODE_ID"), we switched to the generic implementation of cpu_to_node(), which uses a percpu variable to hold the NUMA node for each CPU.

Unfortunately we neglected to notice that we use cpu_to_node() in the allocation of our percpu areas, leading to a chicken and egg problem. In practice what happens is when we are setting up the percpu areas, cpu_to_node() reports that all CPUs are on node 0, so we allocate all percpu areas on node 0.

This is visible in the dmesg output, as all pcpu allocs being in group 0:

pcpu-alloc: [0] 00 01 02 03 [0] 04 05 06 07
pcpu-alloc: [0] 08 09 10 11 [0] 12 13 14 15
pcpu-alloc: [0] 16 17 18 19 [0] 20 21 22 23
pcpu-alloc: [0] 24 25 26 27 [0] 28 29 30 31
pcpu-alloc: [0] 32 33 34 35 [0] 36 37 38 39
pcpu-alloc: [0] 40 41 42 43 [0] 44 45 46 47

To fix it we need an early_cpu_to_node() which can run prior to percpu being setup. We already have the numa_cpu_lookup_table we can use, so just plumb it in. With the patch dmesg output shows two groups, 0 and 1:

pcpu-alloc: [0] 00 01 02 03 [0] 04 05 06 07
pcpu-alloc: [0] 08 09 10 11 [0] 12 13 14 15
pcpu-alloc: [0] 16 17 18 19 [0] 20 21 22 23
pcpu-alloc: [1] 24 25 26 27 [1] 28 29 30 31
pcpu-alloc: [1] 32 33 34 35 [1] 36 37 38 39
pcpu-alloc: [1] 40 41 42 43 [1] 44 45 46 47

We can also check the data_offset in the paca of various CPUs, with the fix we see:

CPU 0: data_offset = 0x0ffe8b0000
CPU 24: data_offset = 0x1ffe5b0000

And we can see from dmesg that CPU 24 has an allocation on node 1:

node 0: [mem 0x0000000000000000-0x0000000fffffffff]
node 1: [mem 0x0000001000000000-0x0000001fffffffff]

---
 arch/powerpc/include/asm/topology.h |   14 ++++++++++++++
 arch/powerpc/kernel/setup_64.c      |    4 ++--
 2 files changed, 16 insertions(+), 2 deletions(-)

@@ -44,8 +44,22 @@ extern void __init dump_numa_cpu_topolog
 extern int sysfs_add_device_to_node(struct device *dev, int nid);
 extern void sysfs_remove_device_from_node(struct device *dev, int nid);
 
+static inline int early_cpu_to_node(int cpu)
+{
+	int nid;
+
+	nid = numa_cpu_lookup_table[cpu];
+
+	/*
+	 * Fall back to node 0 if nid is unset (it should be, except bugs).
+	 * This allows callers to safely do NODE_DATA(early_cpu_to_node(cpu)).
+	 */
+	return (nid < 0) ? 0 : nid;
+}
 #else
 
+static inline int early_cpu_to_node(int cpu) { return 0; }
+
 static inline void dump_numa_cpu_topology(void) {}
 
 static inline int sysfs_add_device_to_node(struct device *dev, int nid)

@@ -595,7 +595,7 @@ void __init emergency_stack_init(void)
 
 static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align)
 {
-	return __alloc_bootmem_node(NODE_DATA(cpu_to_node(cpu)), size, align,
+	return __alloc_bootmem_node(NODE_DATA(early_cpu_to_node(cpu)), size, align,
 				    __pa(MAX_DMA_ADDRESS));
 }
 

@@ -606,7 +606,7 @@ static void __init pcpu_fc_free(void *pt
 
 static int pcpu_cpu_distance(unsigned int from, unsigned int to)
 {
-	if (cpu_to_node(from) == cpu_to_node(to))
+	if (early_cpu_to_node(from) == early_cpu_to_node(to))
 		return LOCAL_DISTANCE;
 	else
 		return REMOTE_DISTANCE;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/cxl-fix-error-path-on-bad-ioctl.patch queue-4.9/powerpc-kernel-fix-fp-and-vector-register-restoration.patch queue-4.9/powerpc-numa-fix-percpu-allocations-to-be-numa-aware.patch queue-4.9/powerpc-kernel-initialize-load_tm-on-task-creation.patch queue-4.9/cxl-avoid-double-free_irq-for-psl-slice-interrupts.patch queue-4.9/powerpc-sysdev-simple_gpio-fix-oops-in-gpio-save_regs-function.patch queue-4.9/powerpc-hotplug-mem-fix-missing-endian-conversion-of-aa_index.patch