From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date: Tue, 26 Jul 2011 00:12:10 +0000 (-0700)
Subject: pagewalk: add locking-rule comments
X-Git-Tag: firefly_0821_release~3680^2~4933^2~101
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c27fe4c8942d3ca715986f79cc26f44608d7d9fb;p=firefly-linux-kernel-4.4.55.git

pagewalk: add locking-rule comments

Originally, walk_hugetlb_range() didn't require a caller take any lock.
But commit d33b9f45bd ("mm: hugetlb: fix hugepage memory leak in
walk_page_range") changed its rule.  Because it added find_vma() call in
walk_hugetlb_range().

Any locking-rule change commit should write a doc too.

[akpm@linux-foundation.org: clarify comment]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6321e840e21d..3c5505a3bc49 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -911,6 +911,8 @@ unsigned long unmap_vmas(struct mmu_gather *tlb,
  * @pte_entry: if set, called for each non-empty PTE (4th-level) entry
  * @pte_hole: if set, called for each hole at all levels
  * @hugetlb_entry: if set, called for each hugetlb entry
+ *		   *Caution*: The caller must hold mmap_sem() if @hugetlb_entry
+ * 			      is used.
  *
  * (see walk_page_range for more details)
  */
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index ee4ff87c58c1..f7929406e776 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -181,6 +181,9 @@ static int walk_hugetlb_range(struct vm_area_struct *vma,
  *
  * If any callback returns a non-zero value, the walk is aborted and
  * the return value is propagated back to the caller. Otherwise 0 is returned.
+ *
+ * walk->mm->mmap_sem must be held for at least read if walk->hugetlb_entry
+ * is !NULL.
  */
 int walk_page_range(unsigned long addr, unsigned long end,
 		    struct mm_walk *walk)