>From 4a3cf5be07a66cf3906a380e77ba5e2ac1b2b3d5 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Sat, 1 Aug 2015 22:39:30 +0900
Subject: [PATCH 1/2] mm: Fix race between setting TIF_MEMDIE and
__alloc_pages_high_priority().
Currently, TIF_MEMDIE is checked at gfp_to_alloc_flags() which is before
calling __alloc_pages_high_priority() and at
/* Avoid allocations with no watermarks from looping endlessly */
if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
which is after returning from __alloc_pages_high_priority(). This means
that if TIF_MEMDIE is set between returning from gfp_to_alloc_flags() and
checking test_thread_flag(TIF_MEMDIE), the allocation can fail without
calling __alloc_pages_high_priority(). We need to replace
"test_thread_flag(TIF_MEMDIE)" with "whether TIF_MEMDIE was already set
as of calling gfp_to_alloc_flags()" in order to close this race window.
Since gfp_to_alloc_flags() includes ALLOC_NO_WATERMARKS for several cases,
it will be more correct to replace "test_thread_flag(TIF_MEMDIE)" with
"whether gfp_to_alloc_flags() included ALLOC_NO_WATERMARKS" because the
purpose of test_thread_flag(TIF_MEMDIE) is to give up immediately if
__alloc_pages_high_priority() failed.
Note that we could simply do
if (alloc_flags & ALLOC_NO_WATERMARKS) {
ac->zonelist = node_zonelist(numa_node_id(), gfp_mask);
page = __alloc_pages_high_priority(gfp_mask, order, ac);
if (page)
goto got_pg;
WARN_ON_ONCE(!wait && (gfp_mask & __GFP_NOFAIL));
goto nopage;
}
instead of changing to
if ((alloc_flags & ALLOC_NO_WATERMARKS) && !(gfp_mask & __GFP_NOFAIL))
goto nopage;
if we can duplicate
if (!wait) {
WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL);
goto nopage;
}
.
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4b220cb..37a0390 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3085,7 +3085,7 @@ retry:
goto nopage;
/* Avoid allocations with no watermarks from looping endlessly */
- if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
+ if ((alloc_flags & ALLOC_NO_WATERMARKS) && !(gfp_mask & __GFP_NOFAIL))
goto nopage;
/*
--
1.8.3.1
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