[PATCH 07/11] mm, madvise_inject_error: fix page count leak

[Dan Williams <dan.j.williams@xxxxxxxxx>]

The madvise_inject_error() routine uses get_user_pages() to lookup the
pfn and other information for injected error, but it fails to release
that pin.

The dax-dma-vs-truncate warning catches this failure with the following
signature:

 Injecting memory failure for pfn 0x208900 at process virtual address 0x7f3908d00000
 Memory failure: 0x208900: reserved kernel page still referenced by 1 users
 Memory failure: 0x208900: recovery action for reserved kernel page: Failed
 WARNING: CPU: 37 PID: 9566 at fs/dax.c:348 dax_disassociate_entry+0x4e/0x90
 CPU: 37 PID: 9566 Comm: umount Tainted: G        W  OE     4.17.0-rc6+ #1900
 [..]
 RIP: 0010:dax_disassociate_entry+0x4e/0x90
 RSP: 0018:ffffc9000a9b3b30 EFLAGS: 00010002
 RAX: ffffea0008224000 RBX: 0000000000208a00 RCX: 0000000000208900
 RDX: 0000000000000001 RSI: ffff8804058c6160 RDI: 0000000000000008
 RBP: 000000000822000a R08: 0000000000000002 R09: 0000000000208800
 R10: 0000000000000000 R11: 0000000000208801 R12: ffff8804058c6168
 R13: 0000000000000000 R14: 0000000000000002 R15: 0000000000000001
 FS:  00007f4548027fc0(0000) GS:ffff880431d40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000056316d5f8988 CR3: 00000004298cc000 CR4: 00000000000406e0
 Call Trace:
  __dax_invalidate_mapping_entry+0xab/0xe0
  dax_delete_mapping_entry+0xf/0x20
  truncate_exceptional_pvec_entries.part.14+0x1d4/0x210
  truncate_inode_pages_range+0x291/0x920
  ? kmem_cache_free+0x1f8/0x300
  ? lock_acquire+0x9f/0x200
  ? truncate_inode_pages_final+0x31/0x50
  ext4_evict_inode+0x69/0x740

Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: bd1ce5f91f54 ("HWPOISON: avoid grabbing the page count...")
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 mm/madvise.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 4d3c922ea1a1..246fa4d4eee2 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -631,11 +631,13 @@ static int madvise_inject_error(int behavior,
 
 
 	for (; start < end; start += PAGE_SIZE << order) {
+		unsigned long pfn;
 		int ret;
 
 		ret = get_user_pages_fast(start, 1, 0, &page);
 		if (ret != 1)
 			return ret;
+		pfn = page_to_pfn(page);
 
 		/*
 		 * When soft offlining hugepages, after migrating the page
@@ -651,17 +653,20 @@ static int madvise_inject_error(int behavior,
 
 		if (behavior == MADV_SOFT_OFFLINE) {
 			pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
-						page_to_pfn(page), start);
+					pfn, start);
 
 			ret = soft_offline_page(page, MF_COUNT_INCREASED);
+			put_page(page);
 			if (ret)
 				return ret;
 			continue;
 		}
+		put_page(page);
+
 		pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
-						page_to_pfn(page), start);
+				pfn, start);
 
-		ret = memory_failure(page_to_pfn(page), MF_COUNT_INCREASED);
+		ret = memory_failure(pfn, MF_COUNT_INCREASED);
 		if (ret)
 			return ret;
 	}