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Tue, 11 Mar 2025 08:30:33 -0700 (PDT) Date: Tue, 11 Mar 2025 11:30:32 -0400 From: Johannes Weiner To: Shakeel Butt Cc: Andrew Morton , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team , stable@vger.kernel.org Subject: Re: [PATCH] memcg: drain obj stock on cpu hotplug teardown Message-ID: <20250311153032.GB1211411@cmpxchg.org> References: <20250310230934.2913113-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250310230934.2913113-1-shakeel.butt@linux.dev> On Mon, Mar 10, 2025 at 04:09:34PM -0700, Shakeel Butt wrote: > Currently on cpu hotplug teardown, only memcg stock is drained but we > need to drain the obj stock as well otherwise we will miss the stats > accumulated on the target cpu as well as the nr_bytes cached. The stats > include MEMCG_KMEM, NR_SLAB_RECLAIMABLE_B & NR_SLAB_UNRECLAIMABLE_B. In > addition we are leaking reference to struct obj_cgroup object. > > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") > Signed-off-by: Shakeel Butt > Cc: Wow, that's old. Good catch. > --- > mm/memcontrol.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4de6acb9b8ec..59dcaf6a3519 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1921,9 +1921,18 @@ void drain_all_stock(struct mem_cgroup *root_memcg) > static int memcg_hotplug_cpu_dead(unsigned int cpu) > { > struct memcg_stock_pcp *stock; > + struct obj_cgroup *old; > + unsigned long flags; > > stock = &per_cpu(memcg_stock, cpu); > + > + /* drain_obj_stock requires stock_lock */ > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > + old = drain_obj_stock(stock); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > + > drain_stock(stock); > + obj_cgroup_put(old); It might be better to call drain_local_stock() directly instead. That would prevent a bug of this type to reoccur in the future.