[PATCH] mm/memory_hotplug: set zone->wait_table to null after free it

[Gu Zheng]

Izumi found the following oops when hot re-add a node:
[ 1481.759192] BUG: unable to handle kernel paging request at ffffc90008963690
[ 1481.760192] IP: [<ffffffff810dff80>] __wake_up_bit+0x20/0x70
[ 1481.770098] PGD 86e919067 PUD 207cf003067 PMD 20796d3b067 PTE 0
[ 1481.770098] Oops: 0000 [#1] SMP
[ 1481.770098] CPU: 68 PID: 1237 Comm: rs:main Q:Reg Not tainted 4.1.0-rc5 #80
[ 1481.770098] Hardware name: FUJITSU PRIMEQUEST2800E/SB, BIOS PRIMEQUEST 2000 Series BIOS Version 1.87 04/28/2015
[ 1481.770098] task: ffff880838df8000 ti: ffff880017b94000 task.ti: ffff880017b94000
[ 1481.770098] RIP: 0010:[<ffffffff810dff80>]  [<ffffffff810dff80>] __wake_up_bit+0x20/0x70
[ 1481.770098] RSP: 0018:ffff880017b97be8  EFLAGS: 00010246
[ 1481.770098] RAX: ffffc90008963690 RBX: 00000000003c0000 RCX: 000000000000a4c9
[ 1481.770098] RDX: 0000000000000000 RSI: ffffea101bffd500 RDI: ffffc90008963648
[ 1481.770098] RBP: ffff880017b97c08 R08: 0000000002000020 R09: 0000000000000000
[ 1481.770098] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8a0797c73800
[ 1481.770098] R13: ffffea101bffd500 R14: 0000000000000001 R15: 00000000003c0000
[ 1481.770098] FS:  00007fcc7ffff700(0000) GS:ffff880874800000(0000) knlGS:0000000000000000
[ 1481.770098] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1481.770098] CR2: ffffc90008963690 CR3: 0000000836761000 CR4: 00000000001407e0
[ 1481.770098] Stack:
[ 1481.770098]  ffff8a0797c73800 ffffea1000000000 0000100000000000 0000000069c53212
[ 1481.770098]  ffff880017b97c18 ffffffff811c2a5d ffff880017b97c68 ffffffff8128a0e3
[ 1481.770098]  0000000000000001 000000281bffd500 00000000003c0000 0000000000000028
[ 1481.770098] Call Trace:
[ 1481.770098]  [<ffffffff811c2a5d>] unlock_page+0x6d/0x70
[ 1481.770098]  [<ffffffff8128a0e3>] generic_write_end+0x53/0xb0
[ 1481.770098]  [<ffffffffa0496559>] xfs_vm_write_end+0x29/0x80 [xfs]
[ 1481.770098]  [<ffffffff811c25da>] generic_perform_write+0x10a/0x1e0
[ 1481.770098]  [<ffffffffa04acb4d>] xfs_file_buffered_aio_write+0x14d/0x3e0 [xfs]
[ 1481.770098]  [<ffffffffa04ace59>] xfs_file_write_iter+0x79/0x120 [xfs]
[ 1481.770098]  [<ffffffff8124aac4>] __vfs_write+0xd4/0x110
[ 1481.770098]  [<ffffffff8124b1ac>] vfs_write+0xac/0x1c0
[ 1481.770098]  [<ffffffff8124c0a8>] SyS_write+0x58/0xd0
[ 1481.770098]  [<ffffffff8177eb6e>] system_call_fastpath+0x12/0x76
[ 1481.770098] Code: 5d c3 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5
 48 83 ec 20 65 48 8b 04 25 28 00 00 00 48 89 45 f8 31 c0 48 8d 47 48 <48> 39 47
 48 48 c7 45 e8 00 00 00 00 48 c7 45 f0 00 00 00 00 48
[ 1481.770098] RIP  [<ffffffff810dff80>] __wake_up_bit+0x20/0x70
[ 1481.770098]  RSP <ffff880017b97be8>
[ 1481.770098] CR2: ffffc90008963690
[ 1481.770098] ---[ end trace 25c9882ad3f72923 ]---
[ 1481.770098] Kernel panic - not syncing: Fatal exception
[ 1481.770098] Kernel Offset: disabled
[ 1481.770098] drm_kms_helper: panic occurred, switching back to text console
[ 1481.770098] ---[ end Kernel panic - not syncing: Fatal exception

Reproduce method (re-add a node):
Hot-add nodeA --> remove nodeA --> hot-add nodeA (panic)

This seems an use-after-free problem, and the root cause is zone->wait_table
was not set to *NULL* after free it in try_offline_node.

When hot re-add a node, we will reuse the pgdat of it, so does
the zone struct, and when add pages to the target zone, it will init the
zone first (including the wait_table) if the zone is not initialized.
The judgement of zone initialized is based on zone->wait_table:
	static inline bool zone_is_initialized(struct zone *zone)
	{
		return !!zone->wait_table;
	},
so if we do not set the zone->wait_table to *NULL* after free it, the memory
hotplug routine will skip the init of new zone when hot re-add the node, and
the wait_table still points to the freed memory, then we will access the invalid
address when trying to wake up the waiting people after the i/o operation with
the page is done, such as mentioned above.

Reported-by: Taku Izumi <izumi.taku@xxxxxxxxxxxxxx>
Cc: Stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
---
 mm/memory_hotplug.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 457bde5..9e88f74 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1969,8 +1969,10 @@ void try_offline_node(int nid)
 		 * wait_table may be allocated from boot memory,
 		 * here only free if it's allocated by vmalloc.
 		 */
-		if (is_vmalloc_addr(zone->wait_table))
+		if (is_vmalloc_addr(zone->wait_table)) {
 			vfree(zone->wait_table);
+			zone->wait_table = NULL;
+		}
 	}
 }
 EXPORT_SYMBOL(try_offline_node);
-- 
1.8.3.1

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