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 1e0d6b2..d8f0766 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -987,25 +987,18 @@
/*
* 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 @@
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;
}