__GFP_NOFAIL specifies that the page allocator cannot fail to return
memory. Allocators that call it may not even check for NULL upon
returning.
It turns out GFP_NOWAIT | __GFP_NOFAIL or GFP_ATOMIC | __GFP_NOFAIL can
actually return NULL. More interestingly, processes that are doing
direct reclaim and have PF_MEMALLOC set may also return NULL for any
__GFP_NOFAIL allocation.
This patch fixes it so that the page allocator never actually returns
NULL as expected for __GFP_NOFAIL. It turns out that no code actually
does anything as crazy as GFP_ATOMIC | __GFP_NOFAIL currently, so this
is more for correctness than a bug fix for that issue.
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
mm/page_alloc.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2535,17 +2535,19 @@ rebalance:
}
}
- /* Atomic allocations - we can't balance anything */
- if (!wait)
- goto nopage;
-
- /* Avoid recursion of direct reclaim */
- if (current->flags & PF_MEMALLOC)
- goto nopage;
-
- /* Avoid allocations with no watermarks from looping endlessly */
- if (test_thread_flag(TIF_MEMDIE) && !(gfp_mask & __GFP_NOFAIL))
- goto nopage;
+ if (likely(!(gfp_mask & __GFP_NOFAIL))) {
+ /* Atomic allocations - we can't balance anything */
+ if (!wait)
+ goto nopage;
+
+ /* Avoid recursion of direct reclaim */
+ if (current->flags & PF_MEMALLOC)
+ goto nopage;
+
+ /* Avoid allocations with no watermarks from looping forever */
+ if (test_thread_flag(TIF_MEMDIE))
+ goto nopage;
+ }
/*
* Try direct compaction. The first pass is asynchronous. Subsequent
--
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