From: Liam R. Howlett <Liam.Howlett@Oracle.com>
Date: Tue, 20 Oct 2020 18:59:58 +0000 (-0400)
Subject: mm/mmap: Fix unnecessary locking of anon_vma on expanding of a vma.
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=55340497ce91f89e3bcd5d085cc3503d8beadf15;p=users%2Fjedix%2Flinux-maple.git

mm/mmap: Fix unnecessary locking of anon_vma on expanding of a vma.

When expanding the end of a vma, it is unnecessary to loc the anon_vma tree for writing
because the spinlock on the vma tree ensures that there are no concurrent vma expansions

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 362698fac7eb..728c62da9f91 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -242,7 +242,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 		 * Always allow shrinking brk.
 		 * do_brk_munmap() may downgrade mmap_lock to read.
 		 */
-		if (brk <= mm->brk) {
+		if (brk <= mm->brk) { // newbrk < oldbrk
 			int ret;
 			/*
 			 * mm->brk must to be protected by write mmap_lock.
@@ -618,35 +618,6 @@ void vma_store(struct mm_struct *mm, struct vm_area_struct *vma)
 	vma_mt_store(mm, vma);
 }
 
-/* vma_mt_brk() - Change the brk vma.
- * */
-void vma_mt_brk(struct vm_area_struct *vma, unsigned long new_end)
-{
-	bool store = false;
-
-	if (vma->anon_vma) {
-		anon_vma_lock_write(vma->anon_vma);
-		anon_vma_interval_tree_pre_update_vma(vma);
-	}
-
-	// changing the back.
-	if (vma->vm_end > new_end) {
-		vma_mt_szero(vma->vm_mm, new_end, vma->vm_end);
-		vmacache_invalidate(vma->vm_mm);
-	} else
-		store = true;
-
-	vma->vm_end = new_end;
-	if (store)
-		vma_mt_store(vma->vm_mm, vma);
-
-
-	if (vma->anon_vma) {
-		anon_vma_interval_tree_post_update_vma(vma);
-		anon_vma_unlock_write(vma->anon_vma);
-	}
-}
-
 static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
 			struct vm_area_struct *prev)
 {
@@ -2933,7 +2904,17 @@ static int do_brk_munmap(struct vm_area_struct *vma, unsigned long newbrk,
 
 	// Change the oldbrk of vma to the newbrk of the munmap area
 	vma_adjust_trans_huge(vma, vma->vm_start, newbrk, 0);
-	vma_mt_brk(vma, newbrk);
+	if (vma->anon_vma) {
+		anon_vma_lock_write(vma->anon_vma);
+		anon_vma_interval_tree_pre_update_vma(vma);
+	}
+	vma_mt_szero(vma->vm_mm, newbrk, vma->vm_end);
+	vma->vm_end = newbrk;
+	vmacache_invalidate(vma->vm_mm);
+	if (vma->anon_vma) {
+		anon_vma_interval_tree_post_update_vma(vma);
+		anon_vma_unlock_write(vma->anon_vma);
+	}
 
 	unmap_pages = vma_pages(&unmap);
 	if (unmap.vm_flags & VM_LOCKED) {
@@ -3008,7 +2989,8 @@ static int do_brk_flags(struct vm_area_struct **brkvma, unsigned long addr,
 		vma = *brkvma;
 		/* Fast path, expand the existing vma if possible */
 		if (vma && ((vma->vm_flags & ~VM_SOFTDIRTY) == flags)){
-			vma_mt_brk(vma, addr + len);
+			vma->vm_end = addr + len;
+			vma_mt_store(vma->vm_mm, vma);
 			goto out;
 		}
 	}