Merge branch 'safe-dirty-tlb-flush'

This merges the patch to fix possible loss of dirty bit on munmap() or
madvice(DONTNEED).  If there are concurrent writers on other CPU's that
have the unmapped/unneeded page in their TLBs, their writes to the page
could possibly get lost if a third CPU raced with the TLB flush and did
a page_mkclean() before the page was fully written.

Admittedly, if you unmap() or madvice(DONTNEED) an area _while_ another
thread is still busy writing to it, you deserve all the lost writes you
could get.  But we kernel people hold ourselves to higher quality
standards than "crazy people deserve to lose", because, well, we've seen
people do all kinds of crazy things.

So let's get it right, just because we can, and we don't have to worry
about it.

* safe-dirty-tlb-flush:
  mm: split 'tlb_flush_mmu()' into tlb flushing and memory freeing parts

1 files changed, 34 insertions, 19 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 93e332d5ed77..037b812a9531 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -232,17 +232,18 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned long
 #endif
 }
 
-void tlb_flush_mmu(struct mmu_gather *tlb)
+static void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 {
-	struct mmu_gather_batch *batch;
-
-	if (!tlb->need_flush)
-		return;
 	tlb->need_flush = 0;
 	tlb_flush(tlb);
 #ifdef CONFIG_HAVE_RCU_TABLE_FREE
 	tlb_table_flush(tlb);
 #endif
+}
+
+static void tlb_flush_mmu_free(struct mmu_gather *tlb)
+{
+	struct mmu_gather_batch *batch;
 
 	for (batch = &tlb->local; batch; batch = batch->next) {
 		free_pages_and_swap_cache(batch->pages, batch->nr);
@@ -251,6 +252,14 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
 	tlb->active = &tlb->local;
 }
 
+void tlb_flush_mmu(struct mmu_gather *tlb)
+{
+	if (!tlb->need_flush)
+		return;
+	tlb_flush_mmu_tlbonly(tlb);
+	tlb_flush_mmu_free(tlb);
+}
+
 /* tlb_finish_mmu
  *	Called at the end of the shootdown operation to free up any resources
  *	that were required.
@@ -1127,8 +1136,10 @@ again:
 			if (PageAnon(page))
 				rss[MM_ANONPAGES]--;
 			else {
-				if (pte_dirty(ptent))
+				if (pte_dirty(ptent)) {
+					force_flush = 1;
 					set_page_dirty(page);
+				}
 				if (pte_young(ptent) &&
 				    likely(!(vma->vm_flags & VM_SEQ_READ)))
 					mark_page_accessed(page);
@@ -1137,9 +1148,10 @@ again:
 			page_remove_rmap(page);
 			if (unlikely(page_mapcount(page) < 0))
 				print_bad_pte(vma, addr, ptent, page);
-			force_flush = !__tlb_remove_page(tlb, page);
-			if (force_flush)
+			if (unlikely(!__tlb_remove_page(tlb, page))) {
+				force_flush = 1;
 				break;
+			}
 			continue;
 		}
 		/*
@@ -1174,18 +1186,11 @@ again:
 
 	add_mm_rss_vec(mm, rss);
 	arch_leave_lazy_mmu_mode();
-	pte_unmap_unlock(start_pte, ptl);
 
-	/*
-	 * mmu_gather ran out of room to batch pages, we break out of
-	 * the PTE lock to avoid doing the potential expensive TLB invalidate
-	 * and page-free while holding it.
-	 */
+	/* Do the actual TLB flush before dropping ptl */
 	if (force_flush) {
 		unsigned long old_end;
 
-		force_flush = 0;
-
 		/*
 		 * Flush the TLB just for the previous segment,
 		 * then update the range to be the remaining
@@ -1193,11 +1198,21 @@ again:
 		 */
 		old_end = tlb->end;
 		tlb->end = addr;
-
-		tlb_flush_mmu(tlb);
-
+		tlb_flush_mmu_tlbonly(tlb);
 		tlb->start = addr;
 		tlb->end = old_end;
+	}
+	pte_unmap_unlock(start_pte, ptl);
+
+	/*
+	 * If we forced a TLB flush (either due to running out of
+	 * batch buffers or because we needed to flush dirty TLB
+	 * entries before releasing the ptl), free the batched
+	 * memory too. Restart if we didn't do everything.
+	 */
+	if (force_flush) {
+		force_flush = 0;
+		tlb_flush_mmu_free(tlb);
 
 		if (addr != end)
 			goto again;