memfd: fix F_SEAL_WRITE after shmem huge page allocated

commit f2b277c4d1c63a85127e8aa2588e9cc3bd21cb99 upstream.

Wangyong reports: after enabling tmpfs filesystem to support transparent
hugepage with the following command:

  echo always > /sys/kernel/mm/transparent_hugepage/shmem_enabled

the docker program tries to add F_SEAL_WRITE through the following
command, but it fails unexpectedly with errno EBUSY:

  fcntl(5, F_ADD_SEALS, F_SEAL_WRITE) = -1.

That is because memfd_tag_pins() and memfd_wait_for_pins() were never
updated for shmem huge pages: checking page_mapcount() against
page_count() is hopeless on THP subpages - they need to check
total_mapcount() against page_count() on THP heads only.

Make memfd_tag_pins() (compared > 1) as strict as memfd_wait_for_pins()
(compared != 1): either can be justified, but given the non-atomic
total_mapcount() calculation, it is better now to be strict.  Bear in
mind that total_mapcount() itself scans all of the THP subpages, when
choosing to take an XA_CHECK_SCHED latency break.

Also fix the unlikely xa_is_value() case in memfd_wait_for_pins(): if a
page has been swapped out since memfd_tag_pins(), then its refcount must
have fallen, and so it can safely be untagged.

Link: https://lkml.kernel.org/r/a4f79248-df75-2c8c-3df-ba3317ccb5da@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Reported-by: wangyong <wang.yong12@zte.com.cn>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: CGEL ZTE <cgel.zte@gmail.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/memfd.c b/mm/memfd.c
index 9e68a4320a0e4c683826e19e6b2d4758fb1c83f8..2d19288a093ea820d68779af509970838b4c8500 100644 (file)
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -34,26 +34,35 @@ static void memfd_tag_pins(struct address_space *mapping)
        void __rcu **slot;
        pgoff_t start;
        struct page *page;
-       unsigned int tagged = 0;
+       int latency = 0;
+       int cache_count;
 
        lru_add_drain();
        start = 0;
 
        xa_lock_irq(&mapping->i_pages);
        radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
+               cache_count = 1;
                page = radix_tree_deref_slot_protected(slot, &mapping->i_pages.xa_lock);
-               if (!page || radix_tree_exception(page)) {
+               if (!page || radix_tree_exception(page) || PageTail(page)) {
                        if (radix_tree_deref_retry(page)) {
                                slot = radix_tree_iter_retry(&iter);
                                continue;
                        }
-               } else if (page_count(page) - page_mapcount(page) > 1) {
-                       radix_tree_tag_set(&mapping->i_pages, iter.index,
-                                          MEMFD_TAG_PINNED);
+               } else {
+                       if (PageTransHuge(page) && !PageHuge(page))
+                               cache_count = HPAGE_PMD_NR;
+                       if (cache_count !=
+                           page_count(page) - total_mapcount(page)) {
+                               radix_tree_tag_set(&mapping->i_pages,
+                                               iter.index, MEMFD_TAG_PINNED);
+                       }
                }
 
-               if (++tagged % 1024)
+               latency += cache_count;
+               if (latency < 1024)
                        continue;
+               latency = 0;
 
                slot = radix_tree_iter_resume(slot, &iter);
                xa_unlock_irq(&mapping->i_pages);
@@ -79,6 +88,7 @@ static int memfd_wait_for_pins(struct address_space *mapping)
        pgoff_t start;
        struct page *page;
        int error, scan;
+       int cache_count;
 
        memfd_tag_pins(mapping);
 
@@ -107,8 +117,12 @@ static int memfd_wait_for_pins(struct address_space *mapping)
                                page = NULL;
                        }
 
-                       if (page &&
-                           page_count(page) - page_mapcount(page) != 1) {
+                       cache_count = 1;
+                       if (page && PageTransHuge(page) && !PageHuge(page))
+                               cache_count = HPAGE_PMD_NR;
+
+                       if (page && cache_count !=
+                           page_count(page) - total_mapcount(page)) {
                                if (scan < LAST_SCAN)
                                        goto continue_resched;