• Laurent Dufour's avatar
    mm: don't rely on system state to detect hot-plug operations · f85086f9
    Laurent Dufour authored
    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():
    
      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
      Call Trace:
        add_memory_resource+0x23c/0x340 (unreliable)
        __add_memory+0x5c/0xf0
        dlpar_add_lmb+0x1b4/0x500
        dlpar_memory+0x1f8/0xb80
        handle_dlpar_errorlog+0xc0/0x190
        dlpar_store+0x198/0x4a0
        kobj_attr_store+0x30/0x50
        sysfs_kf_write+0x64/0x90
        kernfs_fop_write+0x1b0/0x290
        vfs_write+0xe8/0x290
        ksys_write+0xdc/0x130
        system_call_exception+0x160/0x270
        system_call_common+0xf0/0x27c
    
    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: 4fbce633 ("mm/memory_hotplug.c: make register_mem_sect_under_node() a callback of walk_memory_range()")
    Signed-off-by: default avatarLaurent Dufour <ldufour@linux.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
    Reviewed-by: default avatarOscar Salvador <osalvador@suse.de>
    Acked-by: default avatarMichal Hocko <mhocko@suse.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: "Rafael J. Wysocki" <rafael@kernel.org>
    Cc: Fenghua Yu <fenghua.yu@intel.com>
    Cc: Nathan Lynch <nathanl@linux.ibm.com>
    Cc: Scott Cheloha <cheloha@linux.ibm.com>
    Cc: Tony Luck <tony.luck@intel.com>
    Cc: <stable@vger.kernel.org>
    Link: https://lkml.kernel.org/r/20200915094143.79181-3-ldufour@linux.ibm.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f85086f9
node.c 27.4 KB