[PATCH v2 04/13] mm/page_alloc: relax GFP WARN in nolock allocs

[Brendan Jackman]

This WARN forbids setting other flags than __GFP_ACCOUNT but we
unconditionally set the ones in gfp_nolock so they are certainly fine
for the caller to set.

There are other GFP flags that are almost certainly fine to set here;
Willy noted GFP_HIGHMEM, GFP_DMA, GFP_MOVABLE and GFP_HARDWALL. But,
nolock allocation is rather special, so be conservative to try and
ensure we have a chance to think carefully before nontrivial new
usecases arise.

Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/linux-mm/ajS96fWbG4dzP3u3@xxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e31babe2181a1..074e007bf1bc3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5337,7 +5337,8 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
 		return NULL;
 
 	if (alloc_flags & ALLOC_NOLOCK) {
-		VM_WARN_ON_ONCE(gfp & ~__GFP_ACCOUNT);
+		/* Certain other flags could be supported later if needed. */
+		VM_WARN_ON_ONCE(gfp & ~(__GFP_ACCOUNT | gfp_nolock));
 		if (!alloc_trylock_allowed())
 			return NULL;
 		gfp |= gfp_nolock;

-- 
2.54.0