On Mon, Feb 15, 2016 at 03:32:55AM +0200, Grazvydas Ignotas wrote:
> Hi,
>
> since remap_file_pages() rework the following simple program fails.
> I haven't actually bisected this, only know it worked on 3.19 at least
> (I bought a new system now and need 4.2+ for hardware support).
The patch below should fix the issue. Please test.
> If you are curious, the program is an emulator and is using
> remap_file_pages() to implement memory mirroring efficiently (and to
> remap things during run time).
Could you elaborate on this?
Why creating file on tmpfs/shmem (using memfd_create() for example) plus
plain mmap()s wouldn't work for you?
>From 6b8690c3a983a72212db8cd35eb4cab106a195d4 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
Date: Mon, 15 Feb 2016 13:06:16 +0300
Subject: [PATCH] mm: fix regression in remap_file_pages() emulation
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.
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Reported-by: Grazvydas Ignotas <nota...@gmail.com>
---
mm/mmap.c | 34 +++++++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 2f2415a7a688..76d1ec29149b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2664,12 +2664,29 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start,
unsigned long, size,
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;
@@ -2679,9 +2696,16 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start,
unsigned long, size,
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);
--
Kirill A. Shutemov
