linux-kernel - [PATCH 4/4] memcg: make objcg charging nmi safe

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Message-ID: <20250509232859.657525-5-shakeel.butt@linux.dev>
Date: Fri,  9 May 2025 16:28:59 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Vlastimil Babka <vbabka@...e.cz>,
	Alexei Starovoitov <ast@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	bpf@...r.kernel.org,
	linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: [PATCH 4/4] memcg: make objcg charging nmi safe

To enable memcg charged kernel memory allocations from nmi context,
consume_obj_stock() and refill_obj_stock() needs to be nmi safe. With
the simple in_nmi() check, take the slow path of the objcg charging
which handles the charging and memcg stats updates correctly for the nmi
context.

Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
---
 mm/memcontrol.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bba549c1f18c..6cfa3550f300 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2965,6 +2965,9 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	unsigned long flags;
 	bool ret = false;
 
+	if (unlikely(in_nmi()))
+		return ret;
+
 	local_lock_irqsave(&obj_stock.lock, flags);
 
 	stock = this_cpu_ptr(&obj_stock);
@@ -3068,6 +3071,15 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	unsigned long flags;
 	unsigned int nr_pages = 0;
 
+	if (unlikely(in_nmi())) {
+		if (pgdat)
+			__mod_objcg_mlstate(objcg, pgdat, idx, nr_bytes);
+		nr_pages = nr_bytes >> PAGE_SHIFT;
+		nr_bytes = nr_bytes & (PAGE_SIZE - 1);
+		atomic_add(nr_bytes, &objcg->nr_charged_bytes);
+		goto out;
+	}
+
 	local_lock_irqsave(&obj_stock.lock, flags);
 
 	stock = this_cpu_ptr(&obj_stock);
@@ -3091,7 +3103,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	}
 
 	local_unlock_irqrestore(&obj_stock.lock, flags);
-
+out:
 	if (nr_pages)
 		obj_cgroup_uncharge_pages(objcg, nr_pages);
 }
-- 
2.47.1