On 12.06.19 06:02, Anshuman Khandual wrote: > > > On 06/12/2019 03:49 AM, Andrew Morton wrote: >> On Tue, 11 Jun 2019 16:56:13 +0530 Anshuman Khandual <anshuman.khandual@xxxxxxx> wrote: >> >>> Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs >>> entries between memory block and node. It first checks pfn validity with >>> pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config >>> (arm64 has this enabled) pfn_valid_within() calls pfn_valid(). >>> >>> pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID) >>> which scans all mapped memblock regions with memblock_is_map_memory(). This >>> creates a problem in memory hot remove path which has already removed given >>> memory range from memory block with memblock_[remove|free] before arriving >>> at unregister_mem_sect_under_nodes(). Hence get_nid_for_pfn() returns -1 >>> skipping subsequent sysfs_remove_link() calls leaving node <-> memory block >>> sysfs entries as is. Subsequent memory add operation hits BUG_ON() because >>> of existing sysfs entries. >>> >>> [ 62.007176] NUMA: Unknown node for memory at 0x680000000, assuming node 0 >>> [ 62.052517] ------------[ cut here ]------------ >>> [ 62.053211] kernel BUG at mm/memory_hotplug.c:1143! >>> [ 62.053868] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP >>> [ 62.054589] Modules linked in: >>> [ 62.054999] CPU: 19 PID: 3275 Comm: bash Not tainted 5.1.0-rc2-00004-g28cea40b2683 #41 >>> [ 62.056274] Hardware name: linux,dummy-virt (DT) >>> [ 62.057166] pstate: 40400005 (nZcv daif +PAN -UAO) >>> [ 62.058083] pc : add_memory_resource+0x1cc/0x1d8 >>> [ 62.058961] lr : add_memory_resource+0x10c/0x1d8 >>> [ 62.059842] sp : ffff0000168b3ce0 >>> [ 62.060477] x29: ffff0000168b3ce0 x28: ffff8005db546c00 >>> [ 62.061501] x27: 0000000000000000 x26: 0000000000000000 >>> [ 62.062509] x25: ffff0000111ef000 x24: ffff0000111ef5d0 >>> [ 62.063520] x23: 0000000000000000 x22: 00000006bfffffff >>> [ 62.064540] x21: 00000000ffffffef x20: 00000000006c0000 >>> [ 62.065558] x19: 0000000000680000 x18: 0000000000000024 >>> [ 62.066566] x17: 0000000000000000 x16: 0000000000000000 >>> [ 62.067579] x15: ffffffffffffffff x14: ffff8005e412e890 >>> [ 62.068588] x13: ffff8005d6b105d8 x12: 0000000000000000 >>> [ 62.069610] x11: ffff8005d6b10490 x10: 0000000000000040 >>> [ 62.070615] x9 : ffff8005e412e898 x8 : ffff8005e412e890 >>> [ 62.071631] x7 : ffff8005d6b105d8 x6 : ffff8005db546c00 >>> [ 62.072640] x5 : 0000000000000001 x4 : 0000000000000002 >>> [ 62.073654] x3 : ffff8005d7049480 x2 : 0000000000000002 >>> [ 62.074666] x1 : 0000000000000003 x0 : 00000000ffffffef >>> [ 62.075685] Process bash (pid: 3275, stack limit = 0x00000000d754280f) >>> [ 62.076930] Call trace: >>> [ 62.077411] add_memory_resource+0x1cc/0x1d8 >>> [ 62.078227] __add_memory+0x70/0xa8 >>> [ 62.078901] probe_store+0xa4/0xc8 >>> [ 62.079561] dev_attr_store+0x18/0x28 >>> [ 62.080270] sysfs_kf_write+0x40/0x58 >>> [ 62.080992] kernfs_fop_write+0xcc/0x1d8 >>> [ 62.081744] __vfs_write+0x18/0x40 >>> [ 62.082400] vfs_write+0xa4/0x1b0 >>> [ 62.083037] ksys_write+0x5c/0xc0 >>> [ 62.083681] __arm64_sys_write+0x18/0x20 >>> [ 62.084432] el0_svc_handler+0x88/0x100 >>> [ 62.085177] el0_svc+0x8/0xc >> >> This seems like a serious problem. Once which should be fixed in 5.2 >> and perhaps the various -stable kernels as well. > > But the problem does not exist in the current kernel as yet till the reworked > versions of the other two patches in this series get merged. This patch was > after arm64 hot-remove enablement in V1 (https://lkml.org/lkml/2019/4/3/28) > but after some discussions it was decided to be moved before hot-remove from > V2 (https://lkml.org/lkml/2019/4/14/5) onwards as a prerequisite patch instead. > >> >>> Re-ordering memblock_[free|remove]() with arch_remove_memory() solves the >>> problem on arm64 as pfn_valid() behaves correctly and returns positive >>> as memblock for the address range still exists. arch_remove_memory() >>> removes applicable memory sections from zone with __remove_pages() and >>> tears down kernel linear mapping. Removing memblock regions afterwards >>> is safe because there is no other memblock (bootmem) allocator user that >>> late. So nobody is going to allocate from the removed range just to blow >>> up later. Also nobody should be using the bootmem allocated range else >>> we wouldn't allow to remove it. So reordering is indeed safe. >>> >>> ... >>> >>> >>> - Rebased on linux-next (next-20190611) >> >> Yet the patch you've prepared is designed for 5.3. Was that >> deliberate, or should we be targeting earlier kernels? > > It was deliberate for 5.3 as a preparation for upcoming reworked arm64 hot-remove. > We should probably add to the patch description something like "This is a preparation for arm64 memory hotremove. The described issue is not relevant on other architectures." -- Thanks, David / dhildenb
