mm/huge_memory: don't unpoison huge_zero_folio

When I did memory failure tests recently, below panic occurs:

 kernel BUG at include/linux/mm.h:1135!
 invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
 CPU: 9 PID: 137 Comm: kswapd1 Not tainted 6.9.0-rc4-00491-gd5ce28f156fe-dirty #14
 RIP: 0010:shrink_huge_zero_page_scan+0x168/0x1a0
 RSP: 0018:ffff9933c6c57bd0 EFLAGS: 00000246
 RAX: 000000000000003e RBX: 0000000000000000 RCX: ffff88f61fc5c9c8
 RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff88f61fc5c9c0
 RBP: ffffcd7c446b0000 R08: ffffffff9a9405f0 R09: 0000000000005492
 R10: 00000000000030ea R11: ffffffff9a9405f0 R12: 0000000000000000
 R13: 0000000000000000 R14: 0000000000000000 R15: ffff88e703c4ac00
 FS:  0000000000000000(0000) GS:ffff88f61fc40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000055f4da6e9878 CR3: 0000000c71048000 CR4: 00000000000006f0
 Call Trace:
  <TASK>
  do_shrink_slab+0x14f/0x6a0
  shrink_slab+0xca/0x8c0
  shrink_node+0x2d0/0x7d0
  balance_pgdat+0x33a/0x720
  kswapd+0x1f3/0x410
  kthread+0xd5/0x100
  ret_from_fork+0x2f/0x50
  ret_from_fork_asm+0x1a/0x30
  </TASK>
 Modules linked in: mce_inject hwpoison_inject
 ---[ end trace 0000000000000000 ]---
 RIP: 0010:shrink_huge_zero_page_scan+0x168/0x1a0
 RSP: 0018:ffff9933c6c57bd0 EFLAGS: 00000246
 RAX: 000000000000003e RBX: 0000000000000000 RCX: ffff88f61fc5c9c8
 RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff88f61fc5c9c0
 RBP: ffffcd7c446b0000 R08: ffffffff9a9405f0 R09: 0000000000005492
 R10: 00000000000030ea R11: ffffffff9a9405f0 R12: 0000000000000000
 R13: 0000000000000000 R14: 0000000000000000 R15: ffff88e703c4ac00
 FS:  0000000000000000(0000) GS:ffff88f61fc40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000055f4da6e9878 CR3: 0000000c71048000 CR4: 00000000000006f0

The root cause is that HWPoison flag will be set for huge_zero_folio
without increasing the folio refcnt.  But then unpoison_memory() will
decrease the folio refcnt unexpectedly as it appears like a successfully
hwpoisoned folio leading to VM_BUG_ON_PAGE(page_ref_count(page) == 0) when
releasing huge_zero_folio.

Skip unpoisoning huge_zero_folio in unpoison_memory() to fix this issue. 
We're not prepared to unpoison huge_zero_folio yet.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 478d134 ("mm/huge_memory: do not overkill when splitting huge_zero_page")
Signed-off-by: Miaohe Lin <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Xu Yu <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: MiaoheLin

mm/memory-failure.c

@@ -2546,6 +2546,13 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
+	if (is_huge_zero_folio(folio)) {
+		unpoison_pr_info("Unpoison: huge zero page is not supported %#lx\n",
+				 pfn, &unpoison_rs);
+		ret = -EOPNOTSUPP;
+		goto unlock_mutex;
+	}
+
 	if (!PageHWPoison(p)) {
 		unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx\n",
 				 pfn, &unpoison_rs);