[PATCH] mm/pages_alloc.c: Don't create ZONE_MOVABLE beyond the end of a node
From: Alistair Popple
Date: Mon Feb 14 2022 - 22:01:11 EST
ZONE_MOVABLE uses the remaining memory in each node. It's starting pfn
is also aligned to MAX_ORDER_NR_PAGES. It is possible for the remaining
memory in a node to be less than MAX_ORDER_NR_PAGES, meaning there is
not enough room for ZONE_MOVABLE on that node.
Unfortunately this condition is not checked for. This leads to
zone_movable_pfn[] getting set to a pfn greater than the last pfn in a
node.
calculate_node_totalpages() then sets zone->present_pages to be greater
than zone->spanned_pages which is invalid, as spanned_pages represents
the maximum number of pages in a zone assuming no holes.
Subsequently it is possible free_area_init_core() will observe a zone of
size zero with present pages. In this case it will skip setting up the
zone, including the initialisation of free_lists[].
However populated_zone() checks zone->present_pages to see if a zone has
memory available. This is used by iterators such as
walk_zones_in_node(). pagetypeinfo_showfree() uses this to walk the
free_list of each zone in each node, which are assumed to be initialised
due to the zone not being empty. As free_area_init_core() never
initialised the free_lists[] this results in the following kernel crash
when trying to read /proc/pagetypeinfo:
[ 67.534914] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 67.535429] #PF: supervisor read access in kernel mode
[ 67.535789] #PF: error_code(0x0000) - not-present page
[ 67.536128] PGD 0 P4D 0
[ 67.536305] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
[ 67.536696] CPU: 0 PID: 456 Comm: cat Not tainted 5.16.0 #461
[ 67.537096] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
[ 67.537638] RIP: 0010:pagetypeinfo_show+0x163/0x460
[ 67.537992] Code: 9e 82 e8 80 57 0e 00 49 8b 06 b9 01 00 00 00 4c 39 f0 75 16 e9 65 02 00 00 48 83 c1 01 48 81 f9 a0 86 01 00 0f 84 48 02 00 00 <48> 8b 00 4c 39 f0 75 e7 48 c7 c2 80 a2 e2 82 48 c7 c6 79 ef e3 82
[ 67.538259] RSP: 0018:ffffc90001c4bd10 EFLAGS: 00010003
[ 67.538259] RAX: 0000000000000000 RBX: ffff88801105f638 RCX: 0000000000000001
[ 67.538259] RDX: 0000000000000001 RSI: 000000000000068b RDI: ffff8880163dc68b
[ 67.538259] RBP: ffffc90001c4bd90 R08: 0000000000000001 R09: ffff8880163dc67e
[ 67.538259] R10: 656c6261766f6d6e R11: 6c6261766f6d6e55 R12: ffff88807ffb4a00
[ 67.538259] R13: ffff88807ffb49f8 R14: ffff88807ffb4580 R15: ffff88807ffb3000
[ 67.538259] FS: 00007f9c83eff5c0(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
[ 67.538259] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 67.538259] CR2: 0000000000000000 CR3: 0000000013c8e000 CR4: 0000000000350ef0
[ 67.538259] Call Trace:
[ 67.538259] <TASK>
[ 67.538259] seq_read_iter+0x128/0x460
[ 67.538259] ? aa_file_perm+0x1af/0x5f0
[ 67.538259] proc_reg_read_iter+0x51/0x80
[ 67.538259] ? lock_is_held_type+0xea/0x140
[ 67.538259] new_sync_read+0x113/0x1a0
[ 67.538259] vfs_read+0x136/0x1d0
[ 67.538259] ksys_read+0x70/0xf0
[ 67.538259] __x64_sys_read+0x1a/0x20
[ 67.538259] do_syscall_64+0x3b/0xc0
[ 67.538259] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 67.538259] RIP: 0033:0x7f9c83e23cce
[ 67.538259] Code: c0 e9 b6 fe ff ff 50 48 8d 3d 6e 13 0a 00 e8 c9 e3 01 00 66 0f 1f 84 00 00 00 00 00 64 8b 04 25 18 00 00 00 85 c0 75 14 0f 05 <48> 3d 00 f0 ff ff 77 5a c3 66 0f 1f 84 00 00 00 00 00 48 83 ec 28
[ 67.538259] RSP: 002b:00007fff116e1a08 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[ 67.538259] RAX: ffffffffffffffda RBX: 0000000000020000 RCX: 00007f9c83e23cce
[ 67.538259] RDX: 0000000000020000 RSI: 00007f9c83a2c000 RDI: 0000000000000003
[ 67.538259] RBP: 00007f9c83a2c000 R08: 00007f9c83a2b010 R09: 0000000000000000
[ 67.538259] R10: 00007f9c83f2d7d0 R11: 0000000000000246 R12: 0000000000000000
[ 67.538259] R13: 0000000000000003 R14: 0000000000020000 R15: 0000000000020000
[ 67.538259] </TASK>
Fix this by checking that the aligned zone_movable_pfn[] does not exceed
the end of the node, and if it does skip creating a movable zone on this
node.
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
Fixes: 2a1e274acf0b ("Create the ZONE_MOVABLE zone")
---
mm/page_alloc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3589febc6d31..a1fbf656e7db 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7972,10 +7972,17 @@ static void __init find_zone_movable_pfns_for_nodes(void)
out2:
/* Align start of ZONE_MOVABLE on all nids to MAX_ORDER_NR_PAGES */
- for (nid = 0; nid < MAX_NUMNODES; nid++)
+ for (nid = 0; nid < MAX_NUMNODES; nid++) {
+ unsigned long start_pfn, end_pfn;
+
zone_movable_pfn[nid] =
roundup(zone_movable_pfn[nid], MAX_ORDER_NR_PAGES);
+ get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
+ if (zone_movable_pfn[nid] >= end_pfn)
+ zone_movable_pfn[nid] = 0;
+ }
+
out:
/* restore the node_state */
node_states[N_MEMORY] = saved_node_state;
--
2.34.1