On Wed 09-09-20 09:48:59, Laurent Dufour wrote: > 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] Include this into the changelog. > > > 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. I do not follow. register_mem_sect_under_node is about user interface. This is independent on the low level memory representation - aka memory section. I do not think we can handle a section in multiple zones/nodes. Memblock in multiple zones/nodes is a different story and interleaving physical memory layout can indeed lead to it. This is something that we do not allow for runtime hotplug but have to somehow live with that - at least not crash. > > > In > > > 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 > > please? > > 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 OK, so there are two nodes referenced here. Not terrible from the user point of view. Such a memory block will refuse to offline or online IIRC. > > 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. Let me clarify my question. The crash has clearly happened during the hotplug add_memory_resource - which is clearly not a boot time path. I was askin for more information about why this has failed. It is quite clear that sysfs machinery has failed and that led to BUG_ON but we are mising an information on why. What was the physical memory range to be added and why sysfs failed? > > > ------------[ 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 ]--- > > > > 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 > > case. > > > > > 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 > > places. > > 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. I am not sure an enum is going to make the existing situation less messy. Sure we somehow have to distinguish boot init and runtime hotplug because they have different constrains. I am arguing that a) we should have a consistent way to check for those and b) we shouldn't blow up easily just because sysfs infrastructure has failed to initialize. -- Michal Hocko SUSE Labs
