Re: [PATCH] mm: don't rely on system state to detect hot-plug operations

From: Laurent Dufour
Date: Wed Sep 09 2020 - 03:49:32 EST

Le 09/09/2020 à 09:40, Michal Hocko a écrit :
[reposting because the malformed cc list confused my email client]

On Tue 08-09-20 19:08:35, Laurent Dufour wrote:
In register_mem_sect_under_node() the system_state’s value is checked to
detect whether the operation the call is made during boot time or during an
hot-plug operation. Unfortunately, that check is wrong on some
architecture, and may lead to sections being registered under multiple
nodes if node's memory ranges are interleaved.

Why is this check arch specific?

I was wrong the check is not arch specific.

This can be seen on PowerPC LPAR after multiple memory hot-plug and
hot-unplug operations are done. At the next reboot the node's memory ranges
can be interleaved

What is the exact memory layout?

For instance:
[ 0.000000] Early memory node ranges
[ 0.000000] node 1: [mem 0x0000000000000000-0x000000011fffffff]
[ 0.000000] node 2: [mem 0x0000000120000000-0x000000014fffffff]
[ 0.000000] node 1: [mem 0x0000000150000000-0x00000001ffffffff]
[ 0.000000] node 0: [mem 0x0000000200000000-0x000000048fffffff]
[ 0.000000] node 2: [mem 0x0000000490000000-0x00000007ffffffff]

and since the call to link_mem_sections() is made in
topology_init() while the system is in the SYSTEM_SCHEDULING state, the
node's id is not checked, and the sections registered multiple times.

So a single memory section/memblock belongs to two numa nodes?

If the node id is not checked in register_mem_sect_under_node(), yes that the case.

that case, the system is able to boot but later hot-plug operation may lead
to this panic because the node's links are correctly broken:

Correctly broken? Could you provide more details on the inconsistency

laurent@ltczep3-lp4:~$ ls -l /sys/devices/system/memory/memory21
total 0
lrwxrwxrwx 1 root root 0 Aug 24 05:27 node1 -> ../../node/node1
lrwxrwxrwx 1 root root 0 Aug 24 05:27 node2 -> ../../node/node2
-rw-r--r-- 1 root root 65536 Aug 24 05:27 online
-r--r--r-- 1 root root 65536 Aug 24 05:27 phys_device
-r--r--r-- 1 root root 65536 Aug 24 05:27 phys_index
drwxr-xr-x 2 root root 0 Aug 24 05:27 power
-r--r--r-- 1 root root 65536 Aug 24 05:27 removable
-rw-r--r-- 1 root root 65536 Aug 24 05:27 state
lrwxrwxrwx 1 root root 0 Aug 24 05:25 subsystem -> ../../../../bus/memory
-rw-r--r-- 1 root root 65536 Aug 24 05:25 uevent
-r--r--r-- 1 root root 65536 Aug 24 05:27 valid_zones

Which physical memory range you are trying to add here and what is the
node affinity?

None is added, the root cause of the issue is happening at boot time.

------------[ cut here ]------------
kernel BUG at /Users/laurent/src/linux-ppc/mm/memory_hotplug.c:1084!
Oops: Exception in kernel mode, sig: 5 [#1]
Modules linked in: rpadlpar_io rpaphp pseries_rng rng_core vmx_crypto gf128mul binfmt_misc ip_tables x_tables xfs libcrc32c crc32c_vpmsum autofs4
CPU: 8 PID: 10256 Comm: drmgr Not tainted 5.9.0-rc1+ #25
NIP: c000000000403f34 LR: c000000000403f2c CTR: 0000000000000000
REGS: c0000004876e3660 TRAP: 0700 Not tainted (5.9.0-rc1+)
MSR: 800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 24000448 XER: 20040000
CFAR: c000000000846d20 IRQMASK: 0
GPR00: c000000000403f2c c0000004876e38f0 c0000000012f6f00 ffffffffffffffef
GPR04: 0000000000000227 c0000004805ae680 0000000000000000 00000004886f0000
GPR08: 0000000000000226 0000000000000003 0000000000000002 fffffffffffffffd
GPR12: 0000000088000484 c00000001ec96280 0000000000000000 0000000000000000
GPR16: 0000000000000000 0000000000000000 0000000000000004 0000000000000003
GPR20: c00000047814ffe0 c0000007ffff7c08 0000000000000010 c0000000013332c8
GPR24: 0000000000000000 c0000000011f6cc0 0000000000000000 0000000000000000
GPR28: ffffffffffffffef 0000000000000001 0000000150000000 0000000010000000
NIP [c000000000403f34] add_memory_resource+0x244/0x340
LR [c000000000403f2c] add_memory_resource+0x23c/0x340
Call Trace:
[c0000004876e38f0] [c000000000403f2c] add_memory_resource+0x23c/0x340 (unreliable)
[c0000004876e39c0] [c00000000040408c] __add_memory+0x5c/0xf0
[c0000004876e39f0] [c0000000000e2b94] dlpar_add_lmb+0x1b4/0x500
[c0000004876e3ad0] [c0000000000e3888] dlpar_memory+0x1f8/0xb80
[c0000004876e3b60] [c0000000000dc0d0] handle_dlpar_errorlog+0xc0/0x190
[c0000004876e3bd0] [c0000000000dc398] dlpar_store+0x198/0x4a0
[c0000004876e3c90] [c00000000072e630] kobj_attr_store+0x30/0x50
[c0000004876e3cb0] [c00000000051f954] sysfs_kf_write+0x64/0x90
[c0000004876e3cd0] [c00000000051ee40] kernfs_fop_write+0x1b0/0x290
[c0000004876e3d20] [c000000000438dd8] vfs_write+0xe8/0x290
[c0000004876e3d70] [c0000000004391ac] ksys_write+0xdc/0x130
[c0000004876e3dc0] [c000000000034e40] system_call_exception+0x160/0x270
[c0000004876e3e20] [c00000000000d740] system_call_common+0xf0/0x27c
Instruction dump:
48442e35 60000000 0b030000 3cbe0001 7fa3eb78 7bc48402 38a5fffe 7ca5fa14
78a58402 48442db1 60000000 7c7c1b78 <0b030000> 7f23cb78 4bda371d 60000000
---[ end trace 562fd6c109cd0fb2 ]---

The BUG_ON on failure is absolutely horrendous. There must be a better
way to handle a failure like that. The failure means that
sysfs_create_link_nowarn has failed. Please describe why that is the

This patch addresses the root cause by not relying on the system_state
value to detect whether the call is due to a hot-plug operation or not. An
additional parameter is added to link_mem_sections() to tell the context of
the call and this parameter is propagated to register_mem_sect_under_node()
throuugh the walk_memory_blocks()'s call.

This looks like a hack to me and it deserves a better explanation. The
existing code is a hack on its own and it is inconsistent with other
boot time detection. We are using (system_state < SYSTEM_RUNNING) at other
places IIRC. Would it help to use the same here as well? Maybe we want to
wrap that inside a helper (early_memory_init()) and use it at all

I agree, this looks like a hack to check for the system_state value.
I'll follow the David's proposal and introduce an enum detailing when the node id check has to be done or not.
The option of the wrapper seems good to me to, but it doesn't highlight why the early processing is differing from the hot plug one. By using an enum explicitly saying that the node id check is not done seems better to me.

Fixes: 4fbce633910e ("mm/memory_hotplug.c: make register_mem_sect_under_node() a callback of walk_memory_range()")
Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
drivers/base/node.c | 20 +++++++++++++++-----
include/linux/node.h | 6 +++---
mm/memory_hotplug.c | 3 ++-
3 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 508b80f6329b..27f828eeb531 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -762,14 +762,19 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
/* register memory section under specified node if it spans that node */
+struct rmsun_args {
+ int nid;
+ bool hotadd;
static int register_mem_sect_under_node(struct memory_block *mem_blk,
- void *arg)
+ void *args)
unsigned long memory_block_pfns = memory_block_size_bytes() / PAGE_SIZE;
unsigned long start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
unsigned long end_pfn = start_pfn + memory_block_pfns - 1;
- int ret, nid = *(int *)arg;
+ int ret, nid = ((struct rmsun_args *)args)->nid;
unsigned long pfn;
+ bool hotadd = ((struct rmsun_args *)args)->hotadd;
for (pfn = start_pfn; pfn <= end_pfn; pfn++) {
int page_nid;
@@ -789,7 +794,7 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
* case, during hotplug we know that all pages in the memory
* block belong to the same node.
- if (system_state == SYSTEM_BOOTING) {
+ if (!hotadd) {
page_nid = get_nid_for_pfn(pfn);
if (page_nid < 0)
@@ -832,10 +837,15 @@ void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
-int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
+int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
+ bool hotadd)
+ struct rmsun_args args;
+ args.nid = nid;
+ args.hotadd = hotadd;
return walk_memory_blocks(PFN_PHYS(start_pfn),
- PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
+ PFN_PHYS(end_pfn - start_pfn), (void *)&args,
diff --git a/include/linux/node.h b/include/linux/node.h
index 4866f32a02d8..6df9a4548650 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -100,10 +100,10 @@ typedef void (*node_registration_func_t)(struct node *);
extern int link_mem_sections(int nid, unsigned long start_pfn,
- unsigned long end_pfn);
+ unsigned long end_pfn, bool hotadd);
static inline int link_mem_sections(int nid, unsigned long start_pfn,
- unsigned long end_pfn)
+ unsigned long end_pfn, bool hotadd)
return 0;
@@ -128,7 +128,7 @@ static inline int register_one_node(int nid)
if (error)
return error;
/* link memory sections under this node */
- error = link_mem_sections(nid, start_pfn, end_pfn);
+ error = link_mem_sections(nid, start_pfn, end_pfn, false);
return error;
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index e9d5ab5d3ca0..28028db8364a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1080,7 +1080,8 @@ int __ref add_memory_resource(int nid, struct resource *res)
/* link memory sections under this node.*/
- ret = link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1));
+ ret = link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
+ true);
/* create new memmap entry */