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>

1 files changed, 46 insertions, 13 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 1e0d6b237f4..d8f07667fc8 100644
--- 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;
 }