[PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[Laurent Dufour]

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 against SYSTEM_BOOTING is
wrong because regular memory is registered at SYSTEM_SCHEDULING state. In
addition memory hot-plug operation can be triggered at this system state
too by the ACPI. So checking against the system state is not enough.

The consequence is that on system with interleaved node's ranges like this:
 Early memory node ranges
   node   1: [mem 0x0000000000000000-0x000000011fffffff]
   node   2: [mem 0x0000000120000000-0x000000014fffffff]
   node   1: [mem 0x0000000150000000-0x00000001ffffffff]
   node   0: [mem 0x0000000200000000-0x000000048fffffff]
   node   2: [mem 0x0000000490000000-0x00000007ffffffff]

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 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 to multiple nodes:

$ ls -l /sys/devices/system/memory/memory21/node*
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

In that case, the system is able to boot but if later one of theses memory
block is hot-unplugged and then hot-plugged, the sysfs inconsistency is
detected and triggered a BUG_ON():

------------[ cut here ]------------
kernel BUG at /Users/laurent/src/linux-ppc/mm/memory_hotplug.c:1084!
Oops: Exception in kernel mode, sig: 5 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
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 ]---

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. An extra
parameter is needed in register_mem_sect_under_node() detailing whether the
operation is due to a hot-plug operation.

Fixes: 4fbce633910e ("mm/memory_hotplug.c: make register_mem_sect_under_node() a callback of walk_memory_range()")
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Cc: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Hildenbrand <david@redhat.com>
---
 drivers/base/node.c  | 21 ++++++++++++++++-----
 include/linux/node.h |  9 ++++++---
 mm/memory_hotplug.c  |  3 ++-
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 508b80f6329b..862516c5a5ae 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;
+	enum memplug_context context;
+};
 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;
+	enum memplug_context context = ((struct rmsun_args *)args)->context;
 
 	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 (context == MEMPLUG_EARLY) {
 			page_nid = get_nid_for_pfn(pfn);
 			if (page_nid < 0)
 				continue;
@@ -832,10 +837,16 @@ void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
 			  kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
 }
 
-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,
+		      enum memplug_context context)
 {
+	struct rmsun_args args = {
+		.nid = nid,
+		.context = context,
+	};
+
 	return walk_memory_blocks(PFN_PHYS(start_pfn),
-				  PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
+				  PFN_PHYS(end_pfn - start_pfn), (void *)&args,
 				  register_mem_sect_under_node);
 }
 
diff --git a/include/linux/node.h b/include/linux/node.h
index 4866f32a02d8..8ff08520488c 100644
--- a/include/linux/node.h
+++ b/include/linux/node.h
@@ -100,10 +100,12 @@ typedef  void (*node_registration_func_t)(struct node *);
 
 #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_NUMA)
 extern int link_mem_sections(int nid, unsigned long start_pfn,
-			     unsigned long end_pfn);
+			     unsigned long end_pfn,
+			     enum memplug_context context);
 #else
 static inline int link_mem_sections(int nid, unsigned long start_pfn,
-				    unsigned long end_pfn)
+				    unsigned long end_pfn,
+				    enum memplug_context context)
 {
 	return 0;
 }
@@ -128,7 +130,8 @@ 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,
+					  MEMPLUG_EARLY);
 	}
 
 	return error;
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index fc21625e42de..912d355ca446 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),
+				MEMPLUG_HOTPLUG);
 	BUG_ON(ret);
 
 	/* create new memmap entry */
-- 
2.28.0

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[David Hildenbrand]

On 11.09.20 15:48, 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 against SYSTEM_BOOTING is
> wrong because regular memory is registered at SYSTEM_SCHEDULING state. In
> addition memory hot-plug operation can be triggered at this system state
> too by the ACPI. So checking against the system state is not enough.
> 
> The consequence is that on system with interleaved node's ranges like this:
>  Early memory node ranges
>    node   1: [mem 0x0000000000000000-0x000000011fffffff]
>    node   2: [mem 0x0000000120000000-0x000000014fffffff]
>    node   1: [mem 0x0000000150000000-0x00000001ffffffff]
>    node   0: [mem 0x0000000200000000-0x000000048fffffff]
>    node   2: [mem 0x0000000490000000-0x00000007ffffffff]
> 
> 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 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 to multiple nodes:
> 
> $ ls -l /sys/devices/system/memory/memory21/node*
> 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
> 
> In that case, the system is able to boot but if later one of theses memory
> block is hot-unplugged and then hot-plugged, the sysfs inconsistency is
> detected and triggered a BUG_ON():
> 
> ------------[ cut here ]------------
> kernel BUG at /Users/laurent/src/linux-ppc/mm/memory_hotplug.c:1084!
> Oops: Exception in kernel mode, sig: 5 [#1]
> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> 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 ]---
> 
> 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. An extra
> parameter is needed in register_mem_sect_under_node() detailing whether the
> operation is due to a hot-plug operation.
> 
> Fixes: 4fbce633910e ("mm/memory_hotplug.c: make register_mem_sect_under_node() a callback of walk_memory_range()")
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> Cc: stable@vger.kernel.org
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Hildenbrand <david@redhat.com>
> ---
>  drivers/base/node.c  | 21 ++++++++++++++++-----
>  include/linux/node.h |  9 ++++++---
>  mm/memory_hotplug.c  |  3 ++-
>  3 files changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 508b80f6329b..862516c5a5ae 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;
> +	enum memplug_context context;
> +};
>  static int register_mem_sect_under_node(struct memory_block *mem_blk,
> -					 void *arg)
> +					void *args)
>  {

Instead of handling this in register_mem_sect_under_node(), I
think it would be better two have two separate
register_mem_sect_under_node() implementations.

static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
						void *arg)
{
	const int nid = *(int *)arg;
	int ret;

	/* Hotplugged memory has no holes and belongs to a single node. */
	mem_blk->nid = nid;
	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
				       &mem_blk->dev.kobj,
				       kobject_name(&mem_blk->dev.kobj));
	if (ret)
		returnr et;
	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
					&node_devices[nid]->dev.kobj,
					kobject_name(&node_devices[nid]->dev.kobj));

}

Cleaner, right? :) No unnecessary checks.

One could argue if link_mem_section_hotplug() would be better than passing around the context.

-- 
Thanks,

David / dhildenb

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[Laurent Dufour]

Le 14/09/2020 à 09:57, David Hildenbrand a écrit :
> On 11.09.20 15:48, 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 against SYSTEM_BOOTING is
>> wrong because regular memory is registered at SYSTEM_SCHEDULING state. In
>> addition memory hot-plug operation can be triggered at this system state
>> too by the ACPI. So checking against the system state is not enough.
>>
>> The consequence is that on system with interleaved node's ranges like this:
>>   Early memory node ranges
>>     node   1: [mem 0x0000000000000000-0x000000011fffffff]
>>     node   2: [mem 0x0000000120000000-0x000000014fffffff]
>>     node   1: [mem 0x0000000150000000-0x00000001ffffffff]
>>     node   0: [mem 0x0000000200000000-0x000000048fffffff]
>>     node   2: [mem 0x0000000490000000-0x00000007ffffffff]
>>
>> 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 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 to multiple nodes:
>>
>> $ ls -l /sys/devices/system/memory/memory21/node*
>> 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
>>
>> In that case, the system is able to boot but if later one of theses memory
>> block is hot-unplugged and then hot-plugged, the sysfs inconsistency is
>> detected and triggered a BUG_ON():
>>
>> ------------[ cut here ]------------
>> kernel BUG at /Users/laurent/src/linux-ppc/mm/memory_hotplug.c:1084!
>> Oops: Exception in kernel mode, sig: 5 [#1]
>> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
>> 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 ]---
>>
>> 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. An extra
>> parameter is needed in register_mem_sect_under_node() detailing whether the
>> operation is due to a hot-plug operation.
>>
>> Fixes: 4fbce633910e ("mm/memory_hotplug.c: make register_mem_sect_under_node() a callback of walk_memory_range()")
>> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>> Cc: stable@vger.kernel.org
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> ---
>>   drivers/base/node.c  | 21 ++++++++++++++++-----
>>   include/linux/node.h |  9 ++++++---
>>   mm/memory_hotplug.c  |  3 ++-
>>   3 files changed, 24 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/base/node.c b/drivers/base/node.c
>> index 508b80f6329b..862516c5a5ae 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;
>> +	enum memplug_context context;
>> +};
>>   static int register_mem_sect_under_node(struct memory_block *mem_blk,
>> -					 void *arg)
>> +					void *args)
>>   {
> 
> Instead of handling this in register_mem_sect_under_node(), I
> think it would be better two have two separate
> register_mem_sect_under_node() implementations.
> 
> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
> 						void *arg)
> {
> 	const int nid = *(int *)arg;
> 	int ret;
> 
> 	/* Hotplugged memory has no holes and belongs to a single node. */
> 	mem_blk->nid = nid;
> 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> 				       &mem_blk->dev.kobj,
> 				       kobject_name(&mem_blk->dev.kobj));
> 	if (ret)
> 		returnr et;
> 	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> 					&node_devices[nid]->dev.kobj,
> 					kobject_name(&node_devices[nid]->dev.kobj));
> 
> }
> 
> Cleaner, right? :) No unnecessary checks.

Cela me laisse perplexe. Dans un sens, cela simplifie le patch, mais cela 
revient à dupliquer le code pour ne supprimer qu'une seule vérification.

I'm fine with the both options, Ijust want to be sure that all agree on the 
direction before changing my series in that way.

> 
> One could argue if link_mem_section_hotplug() would be better than passing around the context.
>

I do ;)

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[Oscar Salvador]

On Mon, Sep 14, 2020 at 09:57:46AM +0200, David Hildenbrand wrote:
> >  /* register memory section under specified node if it spans that node */
> > +struct rmsun_args {
> > +	int nid;
> > +	enum memplug_context context;
> > +};

Uhmf, that is a not so descriptive name.

> Instead of handling this in register_mem_sect_under_node(), I
> think it would be better two have two separate
> register_mem_sect_under_node() implementations.
> 
> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
> 						void *arg)
> {
> 	const int nid = *(int *)arg;
> 	int ret;
> 
> 	/* Hotplugged memory has no holes and belongs to a single node. */
> 	mem_blk->nid = nid;
> 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> 				       &mem_blk->dev.kobj,
> 				       kobject_name(&mem_blk->dev.kobj));
> 	if (ret)
> 		returnr et;
> 	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> 					&node_devices[nid]->dev.kobj,
> 					kobject_name(&node_devices[nid]->dev.kobj));
> 
> }
> 
> Cleaner, right? :) No unnecessary checks.

I tend to agree here, I like more a simplistic version for hotplug.

> One could argue if link_mem_section_hotplug() would be better than passing around the context.

I am not sure if I would duplicate the code there.
We could just pass the pointer of the function we want to call to
link_mem_sections? either register_mem_sect_under_node_hotplug or
register_mem_sect_under_node_early?
Would not that be clean and clear enough?

-- 
Oscar Salvador
SUSE L3

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[David Hildenbrand]

>> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
>> 						void *arg)
>> {
>> 	const int nid = *(int *)arg;
>> 	int ret;
>>
>> 	/* Hotplugged memory has no holes and belongs to a single node. */
>> 	mem_blk->nid = nid;
>> 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>> 				       &mem_blk->dev.kobj,
>> 				       kobject_name(&mem_blk->dev.kobj));
>> 	if (ret)
>> 		returnr et;
>> 	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>> 					&node_devices[nid]->dev.kobj,
>> 					kobject_name(&node_devices[nid]->dev.kobj));
>>
>> }
>>
>> Cleaner, right? :) No unnecessary checks.
> 
> I tend to agree here, I like more a simplistic version for hotplug.
> 

... and while we're at it, we should rename register_mem_sect_under_node
to something like "register_memory_block_under_node" - "section" is a
legacy leftover here.

We could factor out both sysfs_create_link_nowarn() calls into something
like "do_register_memory_block_under_node" or similar, to minimize code
duplication.

>> One could argue if link_mem_section_hotplug() would be better than passing around the context.
> 
> I am not sure if I would duplicate the code there.
> We could just pass the pointer of the function we want to call to
> link_mem_sections? either register_mem_sect_under_node_hotplug or
> register_mem_sect_under_node_early?
> Would not that be clean and clear enough?

I don't particularly like passing around function pointers where it can
be avoided (e.g., here exporting 3 functions now instead 1). Makes the
interface harder to get IMHO. But I don't really care about that
interface, easy to change later on.

-- 
Thanks,

David / dhildenb

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[Laurent Dufour]

Le 14/09/2020 à 10:31, David Hildenbrand a écrit :
>>> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
>>> 						void *arg)
>>> {
>>> 	const int nid = *(int *)arg;
>>> 	int ret;
>>>
>>> 	/* Hotplugged memory has no holes and belongs to a single node. */
>>> 	mem_blk->nid = nid;
>>> 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>>> 				       &mem_blk->dev.kobj,
>>> 				       kobject_name(&mem_blk->dev.kobj));
>>> 	if (ret)
>>> 		returnr et;
>>> 	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>>> 					&node_devices[nid]->dev.kobj,
>>> 					kobject_name(&node_devices[nid]->dev.kobj));
>>>
>>> }
>>>
>>> Cleaner, right? :) No unnecessary checks.
>>
>> I tend to agree here, I like more a simplistic version for hotplug.
>>
> 
> ... and while we're at it, we should rename register_mem_sect_under_node
> to something like "register_memory_block_under_node" - "section" is a
> legacy leftover here.
> 
> We could factor out both sysfs_create_link_nowarn() calls into something
> like "do_register_memory_block_under_node" or similar, to minimize code
> duplication.
> 
>>> One could argue if link_mem_section_hotplug() would be better than passing around the context.
>>
>> I am not sure if I would duplicate the code there.
>> We could just pass the pointer of the function we want to call to
>> link_mem_sections? either register_mem_sect_under_node_hotplug or
>> register_mem_sect_under_node_early?
>> Would not that be clean and clear enough?
> 
> I don't particularly like passing around function pointers where it can
> be avoided (e.g., here exporting 3 functions now instead 1). Makes the
> interface harder to get IMHO. But I don't really care about that
> interface, easy to change later on.
>

This would lead to the following.

Do everyone agree?

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 508b80f6329b..444808a7c9b6 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -761,9 +761,32 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
  	return pfn_to_nid(pfn);
  }

+static int do_register_memory_block_under_node(int nid,
+					       struct memory_block *mem_blk)
+{
+	int ret;
+
+	/*
+	 * If this memory block spans multiple nodes, we only indicate
+	 * the last processed node.
+	 */
+	mem_blk->nid = nid;
+
+	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
+				       &mem_blk->dev.kobj,
+				       kobject_name(&mem_blk->dev.kobj));
+	if (ret)
+		return ret;
+
+	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
+				&node_devices[nid]->dev.kobj,
+				kobject_name(&node_devices[nid]->dev.kobj));
+
+}
+
  /* register memory section under specified node if it spans that node */
-static int register_mem_sect_under_node(struct memory_block *mem_blk,
-					 void *arg)
+static int register_mem_block_under_node_early(struct memory_block *mem_blk,
+					       void *arg)
  {
  	unsigned long memory_block_pfns = memory_block_size_bytes() / PAGE_SIZE;
  	unsigned long start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
@@ -785,38 +808,35 @@ static int register_mem_sect_under_node(struct 
memory_block *mem_blk,
  		}

  		/*
-		 * We need to check if page belongs to nid only for the boot
-		 * case, during hotplug we know that all pages in the memory
-		 * block belong to the same node.
+		 * We need to check if page belongs to nid only at the boot
+		 * case because node's ranges can be interleaved.
  		 */
-		if (system_state == SYSTEM_BOOTING) {
-			page_nid = get_nid_for_pfn(pfn);
-			if (page_nid < 0)
-				continue;
-			if (page_nid != nid)
-				continue;
-		}
-
-		/*
-		 * If this memory block spans multiple nodes, we only indicate
-		 * the last processed node.
-		 */
-		mem_blk->nid = nid;
+		page_nid = get_nid_for_pfn(pfn);
+		if (page_nid < 0)
+			continue;
+		if (page_nid != nid)
+			continue;

-		ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
-					&mem_blk->dev.kobj,
-					kobject_name(&mem_blk->dev.kobj));
+		ret = do_register_memory_block_under_node(nid, mem_blk);
  		if (ret)
  			return ret;
-
-		return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
-				&node_devices[nid]->dev.kobj,
-				kobject_name(&node_devices[nid]->dev.kobj));
  	}
  	/* mem section does not span the specified node */
  	return 0;
  }

+/*
+ * During hotplug we know that all pages in the memory block belong to the same
+ * node.
+ */
+static int register_mem_block_under_node_hotplug(struct memory_block *mem_blk,
+						 void *arg)
+{
+	int nid = *(int *)arg;
+
+	return do_register_memory_block_under_node(nid, mem_blk);
+}
+
  /*
   * Unregister a memory block device under the node it spans. Memory blocks
   * with multiple nodes cannot be offlined and therefore also never be removed.
@@ -832,11 +852,19 @@ void unregister_memory_block_under_nodes(struct 
memory_block *mem_blk)
  			  kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
  }

-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,
+		      enum memplug_context context)
  {
+	walk_memory_blocks_func_t func;
+
+	if (context == MEMPLUG_HOTPLUG)
+		func = register_mem_block_under_node_hotplug;
+	else
+		func = register_mem_block_under_node_early;
+
  	return walk_memory_blocks(PFN_PHYS(start_pfn),
  				  PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
-				  register_mem_sect_under_node);
+				  func);
  }

  #ifdef CONFIG_HUGETLBFS

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[David Hildenbrand]

On 14.09.20 11:16, Laurent Dufour wrote:
> Le 14/09/2020 à 10:31, David Hildenbrand a écrit :
>>>> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
>>>> 						void *arg)
>>>> {
>>>> 	const int nid = *(int *)arg;
>>>> 	int ret;
>>>>
>>>> 	/* Hotplugged memory has no holes and belongs to a single node. */
>>>> 	mem_blk->nid = nid;
>>>> 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>>>> 				       &mem_blk->dev.kobj,
>>>> 				       kobject_name(&mem_blk->dev.kobj));
>>>> 	if (ret)
>>>> 		returnr et;
>>>> 	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>>>> 					&node_devices[nid]->dev.kobj,
>>>> 					kobject_name(&node_devices[nid]->dev.kobj));
>>>>
>>>> }
>>>>
>>>> Cleaner, right? :) No unnecessary checks.
>>>
>>> I tend to agree here, I like more a simplistic version for hotplug.
>>>
>>
>> ... and while we're at it, we should rename register_mem_sect_under_node
>> to something like "register_memory_block_under_node" - "section" is a
>> legacy leftover here.
>>
>> We could factor out both sysfs_create_link_nowarn() calls into something
>> like "do_register_memory_block_under_node" or similar, to minimize code
>> duplication.
>>
>>>> One could argue if link_mem_section_hotplug() would be better than passing around the context.
>>>
>>> I am not sure if I would duplicate the code there.
>>> We could just pass the pointer of the function we want to call to
>>> link_mem_sections? either register_mem_sect_under_node_hotplug or
>>> register_mem_sect_under_node_early?
>>> Would not that be clean and clear enough?
>>
>> I don't particularly like passing around function pointers where it can
>> be avoided (e.g., here exporting 3 functions now instead 1). Makes the
>> interface harder to get IMHO. But I don't really care about that
>> interface, easy to change later on.
>>
> 
> This would lead to the following.
> 
> Do everyone agree?
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 508b80f6329b..444808a7c9b6 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -761,9 +761,32 @@ static int __ref get_nid_for_pfn(unsigned long pfn)
>   	return pfn_to_nid(pfn);
>   }
> 
> +static int do_register_memory_block_under_node(int nid,
> +					       struct memory_block *mem_blk)
> +{
> +	int ret;
> +
> +	/*
> +	 * If this memory block spans multiple nodes, we only indicate
> +	 * the last processed node.
> +	 */
> +	mem_blk->nid = nid;
> +
> +	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> +				       &mem_blk->dev.kobj,
> +				       kobject_name(&mem_blk->dev.kobj));
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> +				&node_devices[nid]->dev.kobj,
> +				kobject_name(&node_devices[nid]->dev.kobj));
> +
> +}
> +
>   /* register memory section under specified node if it spans that node */
> -static int register_mem_sect_under_node(struct memory_block *mem_blk,
> -					 void *arg)
> +static int register_mem_block_under_node_early(struct memory_block *mem_blk,
> +					       void *arg)
>   {
>   	unsigned long memory_block_pfns = memory_block_size_bytes() / PAGE_SIZE;
>   	unsigned long start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
> @@ -785,38 +808,35 @@ static int register_mem_sect_under_node(struct 
> memory_block *mem_blk,
>   		}
> 
>   		/*
> -		 * We need to check if page belongs to nid only for the boot
> -		 * case, during hotplug we know that all pages in the memory
> -		 * block belong to the same node.
> +		 * We need to check if page belongs to nid only at the boot
> +		 * case because node's ranges can be interleaved.
>   		 */
> -		if (system_state == SYSTEM_BOOTING) {
> -			page_nid = get_nid_for_pfn(pfn);
> -			if (page_nid < 0)
> -				continue;
> -			if (page_nid != nid)
> -				continue;
> -		}
> -
> -		/*
> -		 * If this memory block spans multiple nodes, we only indicate
> -		 * the last processed node.
> -		 */
> -		mem_blk->nid = nid;
> +		page_nid = get_nid_for_pfn(pfn);
> +		if (page_nid < 0)
> +			continue;
> +		if (page_nid != nid)
> +			continue;
> 
> -		ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> -					&mem_blk->dev.kobj,
> -					kobject_name(&mem_blk->dev.kobj));
> +		ret = do_register_memory_block_under_node(nid, mem_blk);
>   		if (ret)
>   			return ret;

You have to do an unconditional

return ret;

here AFAIKS. For me this looks much better.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[Laurent Dufour]

Le 14/09/2020 à 10:19, Oscar Salvador a écrit :
> On Mon, Sep 14, 2020 at 09:57:46AM +0200, David Hildenbrand wrote:
>>>   /* register memory section under specified node if it spans that node */
>>> +struct rmsun_args {
>>> +	int nid;
>>> +	enum memplug_context context;
>>> +};
> 
> Uhmf, that is a not so descriptive name.

I do agree, but didn't have a better idea.
Anyway this will disappear since the choosen direction is to have 2 callbacks.

> 
>> Instead of handling this in register_mem_sect_under_node(), I
>> think it would be better two have two separate
>> register_mem_sect_under_node() implementations.
>>
>> static int register_mem_sect_under_node_hotplug(struct memory_block *mem_blk,
>> 						void *arg)
>> {
>> 	const int nid = *(int *)arg;
>> 	int ret;
>>
>> 	/* Hotplugged memory has no holes and belongs to a single node. */
>> 	mem_blk->nid = nid;
>> 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>> 				       &mem_blk->dev.kobj,
>> 				       kobject_name(&mem_blk->dev.kobj));
>> 	if (ret)
>> 		returnr et;
>> 	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
>> 					&node_devices[nid]->dev.kobj,
>> 					kobject_name(&node_devices[nid]->dev.kobj));
>>
>> }
>>
>> Cleaner, right? :) No unnecessary checks.
> 
> I tend to agree here, I like more a simplistic version for hotplug.
> 
>> One could argue if link_mem_section_hotplug() would be better than passing around the context.
> 
> I am not sure if I would duplicate the code there.
> We could just pass the pointer of the function we want to call to
> link_mem_sections? either register_mem_sect_under_node_hotplug or
> register_mem_sect_under_node_early?
> Would not that be clean and clear enough?

That would expose the register_mem_sect_under_node*() prototype to the caller.

I'm wondering if that would be cleaner than passing a MEMPLUG_* constant value 
to link_mem_sections() and let it choose the right callback.

Re: [PATCH 2/3] mm: don't rely on system state to detect hot-plug operations

[Michal Hocko]

On Fri 11-09-20 15:48:30, 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 against SYSTEM_BOOTING is
> wrong because regular memory is registered at SYSTEM_SCHEDULING state. In
> addition memory hot-plug operation can be triggered at this system state
> too by the ACPI.

Please add
(an example would be Qemu to replay hot added memory after reboot).

> So checking against the system state is not enough.
> 
> The consequence is that on system with interleaved node's ranges like this:
>  Early memory node ranges
>    node   1: [mem 0x0000000000000000-0x000000011fffffff]
>    node   2: [mem 0x0000000120000000-0x000000014fffffff]
>    node   1: [mem 0x0000000150000000-0x00000001ffffffff]
>    node   0: [mem 0x0000000200000000-0x000000048fffffff]
>    node   2: [mem 0x0000000490000000-0x00000007ffffffff]
> 
> 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 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 to multiple nodes:
> 
> $ ls -l /sys/devices/system/memory/memory21/node*
> 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
> 
> In that case, the system is able to boot but if later one of theses memory
> block is hot-unplugged and then hot-plugged, the sysfs inconsistency is
> detected and triggered a BUG_ON():
> 
> ------------[ cut here ]------------
> kernel BUG at /Users/laurent/src/linux-ppc/mm/memory_hotplug.c:1084!
> Oops: Exception in kernel mode, sig: 5 [#1]
> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
> 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 ]---
> 
> 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. An extra
> parameter is needed in register_mem_sect_under_node() detailing whether the
> operation is due to a hot-plug operation.

Thanks this description is much more clear!

> Fixes: 4fbce633910e ("mm/memory_hotplug.c: make register_mem_sect_under_node() a callback of walk_memory_range()")
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> Cc: stable@vger.kernel.org
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Hildenbrand <david@redhat.com>

Wrt to the specific implementation I cannot say I would care much.
Duplicating the code will make the two callers simpler but there will be
a code duplication. We have that weird intermix for hotplug vs. early
init at other places. So I would be very lightly prefering this patch
and do a larger cleanup on top of that. It is at least clear what the
patch does this way. So
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  drivers/base/node.c  | 21 ++++++++++++++++-----
>  include/linux/node.h |  9 ++++++---
>  mm/memory_hotplug.c  |  3 ++-
>  3 files changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 508b80f6329b..862516c5a5ae 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;
> +	enum memplug_context context;
> +};
>  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;
> +	enum memplug_context context = ((struct rmsun_args *)args)->context;
>  
>  	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 (context == MEMPLUG_EARLY) {
>  			page_nid = get_nid_for_pfn(pfn);
>  			if (page_nid < 0)
>  				continue;
> @@ -832,10 +837,16 @@ void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>  			  kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
>  }
>  
> -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,
> +		      enum memplug_context context)
>  {
> +	struct rmsun_args args = {
> +		.nid = nid,
> +		.context = context,
> +	};
> +
>  	return walk_memory_blocks(PFN_PHYS(start_pfn),
> -				  PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
> +				  PFN_PHYS(end_pfn - start_pfn), (void *)&args,
>  				  register_mem_sect_under_node);
>  }
>  
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 4866f32a02d8..8ff08520488c 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -100,10 +100,12 @@ typedef  void (*node_registration_func_t)(struct node *);
>  
>  #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_NUMA)
>  extern int link_mem_sections(int nid, unsigned long start_pfn,
> -			     unsigned long end_pfn);
> +			     unsigned long end_pfn,
> +			     enum memplug_context context);
>  #else
>  static inline int link_mem_sections(int nid, unsigned long start_pfn,
> -				    unsigned long end_pfn)
> +				    unsigned long end_pfn,
> +				    enum memplug_context context)
>  {
>  	return 0;
>  }
> @@ -128,7 +130,8 @@ 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,
> +					  MEMPLUG_EARLY);
>  	}
>  
>  	return error;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index fc21625e42de..912d355ca446 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),
> +				MEMPLUG_HOTPLUG);
>  	BUG_ON(ret);
>  
>  	/* create new memmap entry */
> -- 
> 2.28.0

-- 
Michal Hocko
SUSE Labs