linux-kernel - Re: [PATCH v2 2/5] userfaultfd: non-cooperative: add event for memory unmaps

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Date:   Thu, 2 Feb 2017 10:15:03 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] userfaultfd: non-cooperative: add event for
 memory unmaps

On Fri 27-01-17 20:44:30, Mike Rapoport wrote:
> When a non-cooperative userfaultfd monitor copies pages in the background,
> it may encounter regions that were already unmapped. Addition of
> UFFD_EVENT_UNMAP allows the uffd monitor to track precisely changes in the
> virtual memory layout.
> 
> Since there might be different uffd contexts for the affected VMAs, we
> first should create a temporary representation for the unmap event for each
> uffd context and then notify them one by one to the appropriate userfault
> file descriptors.
> 
> The event notification occurs after the mmap_sem has been released.
> 
> Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>

This breaks NOMMU compilation
---
>From 510948533b059f4f5033464f9f4a0c32d4ab0c08 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Thu, 2 Feb 2017 10:08:47 +0100
Subject: [PATCH] mmotm:
 userfaultfd-non-cooperative-add-event-for-memory-unmaps-fix

This breaks compilation on nommu configs.
mm/nommu.c:1201:15: error: conflicting types for 'do_mmap'
 unsigned long do_mmap(struct file *file,
               ^
In file included from mm/nommu.c:19:0:
./include/linux/mm.h:2089:22: note: previous declaration of 'do_mmap' was here
 extern unsigned long do_mmap(struct file *file, unsigned long addr,
                      ^
mm/nommu.c:1580:5: error: conflicting types for 'do_munmap'
 int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
     ^
In file included from mm/nommu.c:19:0:
./include/linux/mm.h:2093:12: note: previous declaration of 'do_munmap' was here
 extern int do_munmap(struct mm_struct *, unsigned long, size_t,
            ^
make[1]: *** [mm/nommu.o] Error 1

CONFIG_USERFAULTFD depends on CONFIG_MMU so I guess we are OK to just ignore the
argument.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/nommu.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/nommu.c b/mm/nommu.c
index d35088a4b73d..f78d06459ba4 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1205,7 +1205,8 @@ unsigned long do_mmap(struct file *file,
 			unsigned long flags,
 			vm_flags_t vm_flags,
 			unsigned long pgoff,
-			unsigned long *populate)
+			unsigned long *populate,
+			struct list_head *uf_unused)
 {
 	struct vm_area_struct *vma;
 	struct vm_region *region;
@@ -1577,7 +1578,7 @@ static int shrink_vma(struct mm_struct *mm,
  * - under NOMMU conditions the chunk to be unmapped must be backed by a single
  *   VMA, though it need not cover the whole VMA
  */
-int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
+int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list_head *uf)
 {
 	struct vm_area_struct *vma;
 	unsigned long end;
@@ -1643,7 +1644,7 @@ int vm_munmap(unsigned long addr, size_t len)
 	int ret;
 
 	down_write(&mm->mmap_sem);
-	ret = do_munmap(mm, addr, len);
+	ret = do_munmap(mm, addr, len, NULL);
 	up_write(&mm->mmap_sem);
 	return ret;
 }
-- 
2.11.0

-- 
Michal Hocko
SUSE Labs