Merge branch 'locking/urgent' into locking/core, to pick up locking fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 1dfad4536cfe..8e7dc3498e49 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1719,7 +1719,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 	pmd_t pmdval;
 	unsigned long start = addr;
 	bool can_reclaim_pt = reclaim_pt_is_enabled(start, end, details);
-	bool direct_reclaim = false;
+	bool direct_reclaim = true;
 	int nr;
 
 retry:
@@ -1734,8 +1734,10 @@ retry:
 	do {
 		bool any_skipped = false;
 
-		if (need_resched())
+		if (need_resched()) {
+			direct_reclaim = false;
 			break;
+		}
 
 		nr = do_zap_pte_range(tlb, vma, pte, addr, end, details, rss,
 				      &force_flush, &force_break, &any_skipped);
@@ -1743,11 +1745,20 @@ retry:
 			can_reclaim_pt = false;
 		if (unlikely(force_break)) {
 			addr += nr * PAGE_SIZE;
+			direct_reclaim = false;
 			break;
 		}
 	} while (pte += nr, addr += PAGE_SIZE * nr, addr != end);
 
-	if (can_reclaim_pt && addr == end)
+	/*
+	 * Fast path: try to hold the pmd lock and unmap the PTE page.
+	 *
+	 * If the pte lock was released midway (retry case), or if the attempt
+	 * to hold the pmd lock failed, then we need to recheck all pte entries
+	 * to ensure they are still none, thereby preventing the pte entries
+	 * from being repopulated by another thread.
+	 */
+	if (can_reclaim_pt && direct_reclaim && addr == end)
 		direct_reclaim = try_get_and_clear_pmd(mm, pmd, &pmdval);
 
 	add_mm_rss_vec(mm, rss);