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Subject[PATCH 4/6] mm/hotplug: Reorder arch_remove_memory() call in __remove_memory()
Date
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

Re-ordering arch_remove_memory() with memblock_[free|remove] 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 consistent.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
mm/memory_hotplug.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0082d69..71d0d79 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1872,11 +1872,10 @@ void __ref __remove_memory(int nid, u64 start, u64 size)

/* remove memmap entry */
firmware_map_remove(start, start + size, "System RAM");
+ arch_remove_memory(nid, start, size, NULL);
memblock_free(start, size);
memblock_remove(start, size);

- arch_remove_memory(nid, start, size, NULL);
-
try_offline_node(nid);

mem_hotplug_done();
--
2.7.4
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