From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94D7CC433EF for ; Tue, 22 Feb 2022 09:52:33 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C2FF58D0002; Tue, 22 Feb 2022 04:52:32 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BBDEC8D0001; Tue, 22 Feb 2022 04:52:32 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A59418D0002; Tue, 22 Feb 2022 04:52:32 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 91B138D0001 for ; Tue, 22 Feb 2022 04:52:32 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 559A01099 for ; Tue, 22 Feb 2022 09:52:32 +0000 (UTC) X-FDA: 79169950944.03.7906EAD Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf16.hostedemail.com (Postfix) with ESMTP id C223F180017 for ; Tue, 22 Feb 2022 09:52:31 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 7B65721102; Tue, 22 Feb 2022 09:52:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1645523550; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=h6mieIgEvjyuDAfc7uOkZ5vr5OU0GNLS9TFS5R7LVsQ=; b=aJA8FHfv0IKytKEygDLo9BQNAOhxHiT/0nlxPGdGed+2nmb2vntin3IE6p57PatDYvqfSi 76v0c2W0u/X14Kv3T1/nMtTishSMfHOfhHo9YbpJmWy+tKyue+UfZwg06d/WlKZtfk8/AT C4ZAQbd6rhsMPGgKXRgy1lKYH5U5XqI= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 47F6FA3B83; Tue, 22 Feb 2022 09:52:30 +0000 (UTC) Date: Tue, 22 Feb 2022 10:52:29 +0100 From: Michal Hocko To: Sebastian Andrzej Siewior Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Peter Zijlstra , Thomas Gleixner , Vladimir Davydov , Waiman Long , kernel test robot Subject: Re: [PATCH v4 5/6] mm/memcg: Protect memcg_stock with a local_lock_t Message-ID: References: <20220221182540.380526-1-bigeasy@linutronix.de> <20220221182540.380526-6-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220221182540.380526-6-bigeasy@linutronix.de> Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=aJA8FHfv; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf16.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C223F180017 X-Stat-Signature: i64uczacwfwzcw1g8c1qwa98nnnnfdtj X-HE-Tag: 1645523551-689478 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: On Mon 21-02-22 19:25:39, Sebastian Andrzej Siewior wrote: > The members of the per-CPU structure memcg_stock_pcp are protected by > disabling interrupts. This is not working on PREEMPT_RT because it > creates atomic context in which actions are performed which require > preemptible context. One example is obj_cgroup_release(). > > The IRQ-disable sections can be replaced with local_lock_t which > preserves the explicit disabling of interrupts while keeps the code > preemptible on PREEMPT_RT. > > drain_obj_stock() drops a reference on obj_cgroup which leads to an invocation > of obj_cgroup_release() if it is the last object. This in turn leads to > recursive locking of the local_lock_t. To avoid this, obj_cgroup_release() is > invoked outside of the locked section. > > obj_cgroup_uncharge_pages() can be invoked with the local_lock_t acquired and > without it. This will lead later to a recursion in refill_stock(). To > avoid the locking recursion provide obj_cgroup_uncharge_pages_locked() > which uses the locked version of refill_stock(). > > - Replace disabling interrupts for memcg_stock with a local_lock_t. > > - Let drain_obj_stock() return the old struct obj_cgroup which is passed > to obj_cgroup_put() outside of the locked section. > > - Provide obj_cgroup_uncharge_pages_locked() which uses the locked > version of refill_stock() to avoid recursive locking in > drain_obj_stock(). > > Link: https://lkml.kernel.org/r/20220209014709.GA26885@xsang-OptiPlex-9020 > Reported-by: kernel test robot > Signed-off-by: Sebastian Andrzej Siewior Thank you, this looks much more straightforward. I am not super fan of the requirement to call obj_cgroup_put oudside of drain_obj_stock but I can live with that. A comment in drain_obj_stock to call that out explicitly would be nice (can be done as a follow up and have Andrew fold it in if there is no new resubmission). Acked-by: Michal Hocko > --- > mm/memcontrol.c | 55 ++++++++++++++++++++++++++++++------------------- > 1 file changed, 34 insertions(+), 21 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index cd3950256519d..3d7ccb104374c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2128,6 +2128,7 @@ void unlock_page_memcg(struct page *page) > } > > struct memcg_stock_pcp { > + local_lock_t stock_lock; > struct mem_cgroup *cached; /* this never be root cgroup */ > unsigned int nr_pages; > > @@ -2143,18 +2144,21 @@ struct memcg_stock_pcp { > unsigned long flags; > #define FLUSHING_CACHED_CHARGE 0 > }; > -static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); > +static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = { > + .stock_lock = INIT_LOCAL_LOCK(stock_lock), > +}; > static DEFINE_MUTEX(percpu_charge_mutex); > > #ifdef CONFIG_MEMCG_KMEM > -static void drain_obj_stock(struct memcg_stock_pcp *stock); > +static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock); > static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, > struct mem_cgroup *root_memcg); > static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages); > > #else > -static inline void drain_obj_stock(struct memcg_stock_pcp *stock) > +static inline struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) > { > + return NULL; > } > static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, > struct mem_cgroup *root_memcg) > @@ -2186,7 +2190,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) > if (nr_pages > MEMCG_CHARGE_BATCH) > return ret; > > - local_irq_save(flags); > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > > stock = this_cpu_ptr(&memcg_stock); > if (memcg == stock->cached && stock->nr_pages >= nr_pages) { > @@ -2194,7 +2198,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) > ret = true; > } > > - local_irq_restore(flags); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > > return ret; > } > @@ -2223,6 +2227,7 @@ static void drain_stock(struct memcg_stock_pcp *stock) > static void drain_local_stock(struct work_struct *dummy) > { > struct memcg_stock_pcp *stock; > + struct obj_cgroup *old = NULL; > unsigned long flags; > > /* > @@ -2230,14 +2235,16 @@ static void drain_local_stock(struct work_struct *dummy) > * drain_stock races is that we always operate on local CPU stock > * here with IRQ disabled > */ > - local_irq_save(flags); > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > > stock = this_cpu_ptr(&memcg_stock); > - drain_obj_stock(stock); > + old = drain_obj_stock(stock); > drain_stock(stock); > clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); > > - local_irq_restore(flags); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > + if (old) > + obj_cgroup_put(old); > } > > /* > @@ -2264,9 +2271,9 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) > { > unsigned long flags; > > - local_irq_save(flags); > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > __refill_stock(memcg, nr_pages); > - local_irq_restore(flags); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > } > > /* > @@ -3093,10 +3100,11 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, > enum node_stat_item idx, int nr) > { > struct memcg_stock_pcp *stock; > + struct obj_cgroup *old = NULL; > unsigned long flags; > int *bytes; > > - local_irq_save(flags); > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > stock = this_cpu_ptr(&memcg_stock); > > /* > @@ -3105,7 +3113,7 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, > * changes. > */ > if (stock->cached_objcg != objcg) { > - drain_obj_stock(stock); > + old = drain_obj_stock(stock); > obj_cgroup_get(objcg); > stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) > ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; > @@ -3149,7 +3157,9 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat, > if (nr) > mod_objcg_mlstate(objcg, pgdat, idx, nr); > > - local_irq_restore(flags); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > + if (old) > + obj_cgroup_put(old); > } > > static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) > @@ -3158,7 +3168,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) > unsigned long flags; > bool ret = false; > > - local_irq_save(flags); > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > > stock = this_cpu_ptr(&memcg_stock); > if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) { > @@ -3166,17 +3176,17 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes) > ret = true; > } > > - local_irq_restore(flags); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > > return ret; > } > > -static void drain_obj_stock(struct memcg_stock_pcp *stock) > +static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) > { > struct obj_cgroup *old = stock->cached_objcg; > > if (!old) > - return; > + return NULL; > > if (stock->nr_bytes) { > unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT; > @@ -3226,8 +3236,8 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock) > stock->cached_pgdat = NULL; > } > > - obj_cgroup_put(old); > stock->cached_objcg = NULL; > + return old; > } > > static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, > @@ -3248,14 +3258,15 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, > bool allow_uncharge) > { > struct memcg_stock_pcp *stock; > + struct obj_cgroup *old = NULL; > unsigned long flags; > unsigned int nr_pages = 0; > > - local_irq_save(flags); > + local_lock_irqsave(&memcg_stock.stock_lock, flags); > > stock = this_cpu_ptr(&memcg_stock); > if (stock->cached_objcg != objcg) { /* reset if necessary */ > - drain_obj_stock(stock); > + old = drain_obj_stock(stock); > obj_cgroup_get(objcg); > stock->cached_objcg = objcg; > stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) > @@ -3269,7 +3280,9 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, > stock->nr_bytes &= (PAGE_SIZE - 1); > } > > - local_irq_restore(flags); > + local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > + if (old) > + obj_cgroup_put(old); > > if (nr_pages) > obj_cgroup_uncharge_pages(objcg, nr_pages); > -- > 2.35.1 -- Michal Hocko SUSE Labs