linux-kernel - [PATCH 1/2] fork: check charging success before zeroing stack

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Message-Id: <20250829-fork-cleanups-for-dynstack-v1-1-3bbaadce1f00@linaro.org>
Date: Fri, 29 Aug 2025 13:44:40 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
 Juri Lelli <juri.lelli@...hat.com>, 
 Vincent Guittot <vincent.guittot@...aro.org>, 
 Dietmar Eggemann <dietmar.eggemann@....com>, 
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, 
 Kees Cook <kees@...nel.org>, David Hildenbrand <david@...hat.com>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, 
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
 Pasha Tatashin <pasha.tatashin@...een.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
 Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH 1/2] fork: check charging success before zeroing stack

From: Pasha Tatashin <pasha.tatashin@...een.com>

No need to do zero cached stack if memcg charge fails, so move the
charging attempt before the memset operation.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Link: https://lore.kernel.org/20240311164638.2015063-6-pasha.tatashin@soleen.com
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 kernel/fork.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index af673856499dcaa35e135a9e8042ef28d5c5370d..2a5b7a5fa09b1f3a42473cf44a1316ec8b3b31d0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -290,6 +290,11 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 		if (!vm_area)
 			continue;

+		if (memcg_charge_kernel_stack(vm_area)) {
+			vfree(vm_area->addr);
+			return -ENOMEM;
+		}
+
 		/* Reset stack metadata. */
 		kasan_unpoison_range(vm_area->addr, THREAD_SIZE);

@@ -298,11 +303,6 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 		/* Clear stale pointers from reused stack. */
 		memset(stack, 0, THREAD_SIZE);

-		if (memcg_charge_kernel_stack(vm_area)) {
-			vfree(vm_area->addr);
-			return -ENOMEM;
-		}
-
 		tsk->stack_vm_area = vm_area;
 		tsk->stack = stack;
 		return 0;

-- 
2.50.1