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Tue, 11 Mar 2025 10:29:47 -0700 (PDT) Date: Tue, 11 Mar 2025 13:29:47 -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: <20250311172947.GC1211411@cmpxchg.org> References: <20250310230934.2913113-1-shakeel.butt@linux.dev> <20250311153032.GB1211411@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1D9221A0002 X-Stat-Signature: qto3g8rm19cgea59579c8yjfd9gmsqt5 X-Rspam-User: X-HE-Tag: 1741714190-638798 X-HE-Meta: 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 y8P0o2FK 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 11, 2025 at 08:57:54AM -0700, Shakeel Butt wrote: > On Tue, Mar 11, 2025 at 11:30:32AM -0400, Johannes Weiner wrote: > > 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. > > The issue is drain_local_stock() works on the local cpu stock while here > we are working on a remote cpu cpu which is dead (memcg_hotplug_cpu_dead > is in PREPARE section of hotplug teardown which runs after the cpu is > dead). > > We can safely call drain_stock() on remote cpu stock here but > drain_obj_stock() is a bit tricky as it can __refill_stock() to local cpu > stock and can call __mod_objcg_mlstate to flush stats. Both of these > requires irq disable for NON-RT kernels and thus I added the local_lock > here. > > Anyways I wanted a simple fix for the backports and in parallel I am > working on cleaning up all the stock functions as I plan to add multi > memcg support. True, it can be refactored separately. Acked-by: Johannes Weiner