linux-kernel - [PATCH] mm/page_alloc: Fix try_alloc

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Message-Id: <20250401032336.39657-1-alexei.starovoitov@gmail.com>
Date: Mon, 31 Mar 2025 20:23:36 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: bpf@...r.kernel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...nel.org,
	akpm@...ux-foundation.org,
	peterz@...radead.org,
	vbabka@...e.cz,
	bigeasy@...utronix.de,
	rostedt@...dmis.org,
	shakeel.butt@...ux.dev,
	mhocko@...e.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] mm/page_alloc: Fix try_alloc_pages

From: Alexei Starovoitov <ast@...nel.org>

Fix an obvious bug. try_alloc_pages() should set_page_refcounted.

Fixes: 97769a53f117 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation")
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
---

As soon as I fast forwarded and rerun the tests the bug was
seen immediately.
I'm completely baffled how I managed to lose this hunk.
I'm pretty sure I manually tested various code paths of
trylock logic with CONFIG_DEBUG_VM=y.
Pure incompetence :(
Shame.
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ffbb5678bc2f..c0bcfe9d0dd9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7248,6 +7248,9 @@ struct page *try_alloc_pages_noprof(int nid, unsigned int order)
 
 	/* Unlike regular alloc_pages() there is no __alloc_pages_slowpath(). */
 
+	if (page)
+		set_page_refcounted(page);
+
 	if (memcg_kmem_online() && page &&
 	    unlikely(__memcg_kmem_charge_page(page, alloc_gfp, order) != 0)) {
 		free_pages_nolock(page, order);
-- 
2.47.1