mm: no get_user/put_user while holding mmap_sem in do_pages_stat?

Since commit 2f007e74bb85b9fc4eab28524052161703300f1a, do_pages_stat()
gets the page address from user-space and puts the corresponding status
back while holding the mmap_sem for read.  There is no need to hold
mmap_sem there while some page-faults may occur.

This patch adds a temporary address and status buffer so as to only
hold mmap_sem while working on these kernel buffers.  This is
implemented by extracting do_pages_stat_array() out of do_pages_stat().

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 1e0d6b237f4418c2f8b8ca50e88d85a787adc0a7..d8f07667fc8045e6690ab74a6e58806c7093ed7c 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -987,25 +987,18 @@ out:
 /*
  * Determine the nodes of an array of pages and store it in an array of status.
  */
-static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
-                        const void __user * __user *pages,
-                        int __user *status)
+static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
+                               const void __user **pages, int *status)
 {
        unsigned long i;
-       int err;
 
        down_read(&mm->mmap_sem);
 
        for (i = 0; i < nr_pages; i++) {
-               const void __user *p;
-               unsigned long addr;
+               unsigned long addr = (unsigned long)(*pages);
                struct vm_area_struct *vma;
                struct page *page;
-
-               err = -EFAULT;
-               if (get_user(p, pages+i))
-                       goto out;
-               addr = (unsigned long) p;
+               int err;
 
                vma = find_vma(mm, addr);
                if (!vma)
@@ -1024,12 +1017,52 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
 
                err = page_to_nid(page);
 set_status:
-               put_user(err, status+i);
+               *status = err;
+
+               pages++;
+               status++;
+       }
+
+       up_read(&mm->mmap_sem);
+}
+
+/*
+ * Determine the nodes of a user array of pages and store it in
+ * a user array of status.
+ */
+static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
+                        const void __user * __user *pages,
+                        int __user *status)
+{
+#define DO_PAGES_STAT_CHUNK_NR 16
+       const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
+       int chunk_status[DO_PAGES_STAT_CHUNK_NR];
+       unsigned long i, chunk_nr = DO_PAGES_STAT_CHUNK_NR;
+       int err;
+
+       for (i = 0; i < nr_pages; i += chunk_nr) {
+               if (chunk_nr + i > nr_pages)
+                       chunk_nr = nr_pages - i;
+
+               err = copy_from_user(chunk_pages, &pages[i],
+                                    chunk_nr * sizeof(*chunk_pages));
+               if (err) {
+                       err = -EFAULT;
+                       goto out;
+               }
+
+               do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
+
+               err = copy_to_user(&status[i], chunk_status,
+                                  chunk_nr * sizeof(*chunk_status));
+               if (err) {
+                       err = -EFAULT;
+                       goto out;
+               }
        }
        err = 0;
 
 out:
-       up_read(&mm->mmap_sem);
        return err;
 }