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Subject[PATCH v3] powerpc/pseries: Fix cpu_hotplug_lock acquisition in resize_hpt()
From: "Gautham R. Shenoy" <>

The calls to arch_add_memory()/arch_remove_memory() are always made
with the read-side cpu_hotplug_lock acquired via
memory_hotplug_begin(). On pSeries,
arch_add_memory()/arch_remove_memory() eventually call resize_hpt()
which in turn calls stop_machine() which acquires the read-side
cpu_hotplug_lock again, thereby resulting in the recursive acquisition
of this lock.

Lockdep complains as follows in these code-paths.

swapper/0/1 is trying to acquire lock:
(____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: stop_machine+0x2c/0x60

but task is already holding lock:
(____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: mem_hotplug_begin+0x20/0x50

other info that might help us debug this:
Possible unsafe locking scenario:


*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by swapper/0/1:
#0: (____ptrval____) (&dev->mutex){....}, at: __driver_attach+0x12c/0x1b0
#1: (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: mem_hotplug_begin+0x20/0x50
#2: (____ptrval____) (mem_hotplug_lock.rw_sem){++++}, at: percpu_down_write+0x54/0x1a0

stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc5-58373-gbc99402235f3-dirty #166
Call Trace:
[c0000000feb03150] [c000000000e32bd4] dump_stack+0xe8/0x164 (unreliable)
[c0000000feb031a0] [c00000000020d6c0] __lock_acquire+0x1110/0x1c70
[c0000000feb03320] [c00000000020f080] lock_acquire+0x240/0x290
[c0000000feb033e0] [c00000000017f554] cpus_read_lock+0x64/0xf0
[c0000000feb03420] [c00000000029ebac] stop_machine+0x2c/0x60
[c0000000feb03460] [c0000000000d7f7c] pseries_lpar_resize_hpt+0x19c/0x2c0
[c0000000feb03500] [c0000000000788d0] resize_hpt_for_hotplug+0x70/0xd0
[c0000000feb03570] [c000000000e5d278] arch_add_memory+0x58/0xfc
[c0000000feb03610] [c0000000003553a8] devm_memremap_pages+0x5e8/0x8f0
[c0000000feb036c0] [c0000000009c2394] pmem_attach_disk+0x764/0x830
[c0000000feb037d0] [c0000000009a7c38] nvdimm_bus_probe+0x118/0x240
[c0000000feb03860] [c000000000968500] really_probe+0x230/0x4b0
[c0000000feb038f0] [c000000000968aec] driver_probe_device+0x16c/0x1e0
[c0000000feb03970] [c000000000968ca8] __driver_attach+0x148/0x1b0
[c0000000feb039f0] [c0000000009650b0] bus_for_each_dev+0x90/0x130
[c0000000feb03a50] [c000000000967dd4] driver_attach+0x34/0x50
[c0000000feb03a70] [c000000000967068] bus_add_driver+0x1a8/0x360
[c0000000feb03b00] [c00000000096a498] driver_register+0x108/0x170
[c0000000feb03b70] [c0000000009a7400] __nd_driver_register+0xd0/0xf0
[c0000000feb03bd0] [c00000000128aa90] nd_pmem_driver_init+0x34/0x48
[c0000000feb03bf0] [c000000000010a10] do_one_initcall+0x1e0/0x45c
[c0000000feb03cd0] [c00000000122462c] kernel_init_freeable+0x540/0x64c
[c0000000feb03db0] [c00000000001110c] kernel_init+0x2c/0x160
[c0000000feb03e20] [c00000000000bed4] ret_from_kernel_thread+0x5c/0x68

Fix this issue by
1) Requiring all the calls to pseries_lpar_resize_hpt() be made
with cpu_hotplug_lock held.

2) In pseries_lpar_resize_hpt() invoke stop_machine_cpuslocked()
as a consequence of 1)

3) To satisfy 1), in hpt_order_set(), call mmu_hash_ops.resize_hpt()
with cpu_hotplug_lock held.

Reported-by: Aneesh Kumar K.V <>
Signed-off-by: Gautham R. Shenoy <>
v2 -> v3 : Updated the comment for pseries_lpar_resize_hpt()
Updated the commit-log with the full backtrace.
v1 -> v2 : Rebased against powerpc/next instead of linux/master

arch/powerpc/mm/book3s64/hash_utils.c | 9 ++++++++-
arch/powerpc/platforms/pseries/lpar.c | 8 ++++++--
2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 919a861..d07fcafd 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -38,6 +38,7 @@
#include <linux/libfdt.h>
#include <linux/pkeys.h>
#include <linux/hugetlb.h>
+#include <linux/cpu.h>

#include <asm/debugfs.h>
#include <asm/processor.h>
@@ -1928,10 +1929,16 @@ static int hpt_order_get(void *data, u64 *val)

static int hpt_order_set(void *data, u64 val)
+ int ret;
if (!mmu_hash_ops.resize_hpt)
return -ENODEV;

- return mmu_hash_ops.resize_hpt(val);
+ cpus_read_lock();
+ ret = mmu_hash_ops.resize_hpt(val);
+ cpus_read_unlock();
+ return ret;

DEFINE_DEBUGFS_ATTRIBUTE(fops_hpt_order, hpt_order_get, hpt_order_set, "%llu\n");
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 1034ef1..557d592 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -859,7 +859,10 @@ static int pseries_lpar_resize_hpt_commit(void *data)
return 0;

-/* Must be called in user context */
+ * Must be called in process context. The caller must hold the
+ * cpus_lock.
+ */
static int pseries_lpar_resize_hpt(unsigned long shift)
struct hpt_resize_state state = {
@@ -913,7 +916,8 @@ static int pseries_lpar_resize_hpt(unsigned long shift)

t1 = ktime_get();

- rc = stop_machine(pseries_lpar_resize_hpt_commit, &state, NULL);
+ rc = stop_machine_cpuslocked(pseries_lpar_resize_hpt_commit,
+ &state, NULL);

t2 = ktime_get();

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