[patch alternative] mm, page_alloc: warn for non-blockable __GFP_NOFAILallocation failure

[David Rientjes]

__GFP_NOFAIL may return NULL when coupled with GFP_NOWAIT or GFP_ATOMIC.

Luckily, nothing currently does such craziness.  So instead of causing
such allocations to loop (potentially forever), we maintain the current
behavior and also warn about the new users of the deprecated flag.

Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 mm/page_alloc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2536,8 +2536,15 @@ rebalance:
 	}
 
 	/* Atomic allocations - we can't balance anything */
-	if (!wait)
+	if (!wait) {
+		/*
+		 * All existing users of the deprecated __GFP_NOFAIL are
+		 * blockable, so warn of any new users that actually allow this
+		 * type of allocation to fail.
+		 */
+		WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL);
 		goto nopage;
+	}
 
 	/* Avoid recursion of direct reclaim */
 	if (current->flags & PF_MEMALLOC)
--
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