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: <[email protected]>
Fixes: bd1ce5f91f54 ("HWPOISON: avoid grabbing the page count...")
Cc: Michal Hocko <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Wu Fengguang <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
---
 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;
        }

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