Re: [PATCH v3 2/3] mm: don't rely on system state to detect hot-plug operations

[Michal Hocko <mhocko@suse.com>]

On Tue 15-09-20 11:41:42, Laurent Dufour wrote:
> In register_mem_sect_under_node() the system_state’s value is checked to
> detect whether 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
> by the ACPI [1]. 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
> blocks is hot-unplugged and then hot-plugged, the sysfs inconsistency is
> detected and this is triggering 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 added to link_mem_sections() detailing whether the operation
> is due to a hot-plug operation.
> 
> [1] According to Oscar Salvador, using this qemu command line, ACPI memory
> hotplug operations are raised at SYSTEM_SCHEDULING state:
> 
> $QEMU -enable-kvm -machine pc -smp 4,sockets=4,cores=1,threads=1 -cpu host -monitor pty \
>         -m size=$MEM,slots=255,maxmem=4294967296k  \
>         -numa node,nodeid=0,cpus=0-3,mem=512 -numa node,nodeid=1,mem=512 \
>         -object memory-backend-ram,id=memdimm0,size=134217728 -device pc-dimm,node=0,memdev=memdimm0,id=dimm0,slot=0 \
>         -object memory-backend-ram,id=memdimm1,size=134217728 -device pc-dimm,node=0,memdev=memdimm1,id=dimm1,slot=1 \
>         -object memory-backend-ram,id=memdimm2,size=134217728 -device pc-dimm,node=0,memdev=memdimm2,id=dimm2,slot=2 \
>         -object memory-backend-ram,id=memdimm3,size=134217728 -device pc-dimm,node=0,memdev=memdimm3,id=dimm3,slot=3 \
>         -object memory-backend-ram,id=memdimm4,size=134217728 -device pc-dimm,node=1,memdev=memdimm4,id=dimm4,slot=4 \
>         -object memory-backend-ram,id=memdimm5,size=134217728 -device pc-dimm,node=1,memdev=memdimm5,id=dimm5,slot=5 \
>         -object memory-backend-ram,id=memdimm6,size=134217728 -device pc-dimm,node=1,memdev=memdimm6,id=dimm6,slot=6 \
> 
> 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>
> Reviewed-by: David Hildenbrand <david@redhat.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: Oscar Salvador <osalvador@suse.de>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  drivers/base/node.c  | 85 ++++++++++++++++++++++++++++----------------
>  include/linux/node.h | 11 +++---
>  mm/memory_hotplug.c  |  3 +-
>  3 files changed, 64 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 508b80f6329b..50af16e68d98 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -761,14 +761,36 @@ 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);
>  	unsigned long end_pfn = start_pfn + memory_block_pfns - 1;
> -	int ret, nid = *(int *)arg;
> +	int nid = *(int *)arg;
>  	unsigned long pfn;
>  
>  	for (pfn = start_pfn; pfn <= end_pfn; pfn++) {
> @@ -785,38 +807,33 @@ 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.
> -		 */
> -		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.
> +		 * We need to check if page belongs to nid only at the boot
> +		 * case because node's ranges can be interleaved.
>  		 */
> -		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;
> +		page_nid = get_nid_for_pfn(pfn);
> +		if (page_nid < 0)
> +			continue;
> +		if (page_nid != nid)
> +			continue;
>  
> -		return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> -				&node_devices[nid]->dev.kobj,
> -				kobject_name(&node_devices[nid]->dev.kobj));
> +		return do_register_memory_block_under_node(nid, mem_blk);
>  	}
>  	/* 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 +849,19 @@ 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 meminit_context context)
>  {
> +	walk_memory_blocks_func_t func;
> +
> +	if (context == MEMINIT_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
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 4866f32a02d8..014ba3ab2efd 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -99,11 +99,13 @@ extern struct node *node_devices[];
>  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);
> +int link_mem_sections(int nid, unsigned long start_pfn,
> +		      unsigned long end_pfn,
> +		      enum meminit_context context);
>  #else
>  static inline int link_mem_sections(int nid, unsigned long start_pfn,
> -				    unsigned long end_pfn)
> +				    unsigned long end_pfn,
> +				    enum meminit_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,
> +					  MEMINIT_EARLY);
>  	}
>  
>  	return error;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index fc25886ad719..03df20078827 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),
> +				MEMINIT_HOTPLUG);
>  	BUG_ON(ret);
>  
>  	/* create new memmap entry */
> -- 
> 2.28.0
> 

-- 
Michal Hocko
SUSE Labs