+ memcg-no-stock-lock-for-cpu-hot-unplug.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: memcg: no stock lock for cpu hot-unplug
has been added to the -mm mm-new branch.  Its filename is
     memcg-no-stock-lock-for-cpu-hot-unplug.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-no-stock-lock-for-cpu-hot-unplug.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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------------------------------------------------------
From: Shakeel Butt <shakeel.butt@linux.dev>
Subject: memcg: no stock lock for cpu hot-unplug
Date: Wed, 14 May 2025 11:41:57 -0700

Previously on the cpu hot-unplug, the kernel would call drain_obj_stock()
with objcg local lock.  However local lock was not needed as the stock
which was accessed belongs to a dead cpu but we kept it there to disable
irqs as drain_obj_stock() may call mod_objcg_mlstate() which required irqs
disabled.  However there is no need to disable irqs now for
mod_objcg_mlstate(), so we can remove the local lock altogether from cpu
hot-unplug path.

Link: https://lkml.kernel.org/r/20250514184158.3471331-7-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |   11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

--- a/mm/memcontrol.c~memcg-no-stock-lock-for-cpu-hot-unplug
+++ a/mm/memcontrol.c
@@ -2025,17 +2025,8 @@ void drain_all_stock(struct mem_cgroup *
 
 static int memcg_hotplug_cpu_dead(unsigned int cpu)
 {
-	struct obj_stock_pcp *obj_st;
-	unsigned long flags;
-
-	obj_st = &per_cpu(obj_stock, cpu);
-
-	/* drain_obj_stock requires objstock.lock */
-	local_lock_irqsave(&obj_stock.lock, flags);
-	drain_obj_stock(obj_st);
-	local_unlock_irqrestore(&obj_stock.lock, flags);
-
 	/* no need for the local lock */
+	drain_obj_stock(&per_cpu(obj_stock, cpu));
 	drain_stock_fully(&per_cpu(memcg_stock, cpu));
 
 	return 0;
_

Patches currently in -mm which might be from shakeel.butt@linux.dev are

memcg-memcg_rstat_updated-re-entrant-safe-against-irqs.patch
memcg-move-preempt-disable-to-callers-of-memcg_rstat_updated.patch
memcg-make-mod_memcg_state-re-entrant-safe-against-irqs.patch
memcg-make-count_memcg_events-re-entrant-safe-against-irqs.patch
memcg-make-__mod_memcg_lruvec_state-re-entrant-safe-against-irqs.patch
memcg-no-stock-lock-for-cpu-hot-unplug.patch
memcg-objcg-stock-trylock-without-irq-disabling.patch