Patch "mm: fix regression in remap_file_pages() emulation" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

mm: fix regression in remap_file_pages() emulation

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-fix-regression-in-remap_file_pages-emulation.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Kirill A. Shutemov" <[email protected]>
Date: Wed, 17 Feb 2016 13:11:15 -0800
Subject: mm: fix regression in remap_file_pages() emulation

From: Kirill A. Shutemov <[email protected]>

commit 48f7df329474b49d83d0dffec1b6186647f11976 upstream.

Grazvydas Ignotas has reported a regression in remap_file_pages() emulation.

Testcase:

	#define _GNU_SOURCE
	#include <assert.h>
	#include <stdlib.h>
	#include <stdio.h>
	#include <sys/mman.h>

	#define SIZE    (4096 * 3)

	int main(int argc, char **argv)
	{
		unsigned long *p;
		long i;

		p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
				MAP_SHARED | MAP_ANONYMOUS, -1, 0);
		if (p == MAP_FAILED) {
			perror("mmap");
			return -1;
		}

		for (i = 0; i < SIZE / 4096; i++)
			p[i * 4096 / sizeof(*p)] = i;

		if (remap_file_pages(p, 4096, 0, 1, 0)) {
			perror("remap_file_pages");
			return -1;
		}

		if (remap_file_pages(p, 4096 * 2, 0, 1, 0)) {
			perror("remap_file_pages");
			return -1;
		}

		assert(p[0] == 1);

		munmap(p, SIZE);

		return 0;
	}

The second remap_file_pages() fails with -EINVAL.

The reason is that remap_file_pages() emulation assumes that the target vma covers whole area we want to over map. That assumption is broken by first remap_file_pages() call: it split the area into two vma.

The solution is to check next adjacent vmas, if they map the same file with the same flags.

---
 mm/mmap.c |   34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

@@ -2668,12 +2668,29 @@ SYSCALL_DEFINE5(remap_file_pages, unsign
 	if (!vma || !(vma->vm_flags & VM_SHARED))
 		goto out;
 
-	if (start < vma->vm_start || start + size > vma->vm_end)
+	if (start < vma->vm_start)
 		goto out;
 
-	if (pgoff == linear_page_index(vma, start)) {
-		ret = 0;
-		goto out;
+	if (start + size > vma->vm_end) {
+		struct vm_area_struct *next;
+
+		for (next = vma->vm_next; next; next = next->vm_next) {
+			/* hole between vmas ? */
+			if (next->vm_start != next->vm_prev->vm_end)
+				goto out;
+
+			if (next->vm_file != vma->vm_file)
+				goto out;
+
+			if (next->vm_flags != vma->vm_flags)
+				goto out;
+
+			if (start + size <= next->vm_end)
+				break;
+		}
+
+		if (!next)
+			goto out;
 	}
 
 	prot |= vma->vm_flags & VM_READ ? PROT_READ : 0;

@@ -2683,9 +2700,16 @@ SYSCALL_DEFINE5(remap_file_pages, unsign
 	flags &= MAP_NONBLOCK;
 	flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
 	if (vma->vm_flags & VM_LOCKED) {
+		struct vm_area_struct *tmp;
 		flags |= MAP_LOCKED;
+
 		/* drop PG_Mlocked flag for over-mapped range */
-		munlock_vma_pages_range(vma, start, start + size);
+		for (tmp = vma; tmp->vm_start >= start + size;
+				tmp = tmp->vm_next) {
+			munlock_vma_pages_range(tmp,
+					max(tmp->vm_start, start),
+					min(tmp->vm_end, start + size));
+		}
 	}
 
 	file = get_file(vma->vm_file);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mm-thp-khugepaged-call-pte-flush-at-the-time-of-collapse.patch queue-4.4/ipc-shm-handle-removed-segments-gracefully-in-shm_mmap.patch queue-4.4/drivers-scsi-sg.c-mark-vma-as-vm_io-to-prevent-migration.patch queue-4.4/mm-fix-mlock-accouting.patch queue-4.4/mm-replace-vma_lock_anon_vma-with-anon_vma_lock_read-write.patch queue-4.4/mm-fix-regression-in-remap_file_pages-emulation.patch queue-4.4/scsi-add-marvell-console-to-vpd-blacklist.patch