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 X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6948CC4338F for ; Mon, 26 Jul 2021 20:32:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 445C660F23 for ; Mon, 26 Jul 2021 20:32:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232682AbhGZTvr (ORCPT ); Mon, 26 Jul 2021 15:51:47 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:37170 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231650AbhGZTvq (ORCPT ); Mon, 26 Jul 2021 15:51:46 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id D063A1FED5; Mon, 26 Jul 2021 20:32:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1627331533; 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=h1InytiqltbBeRvMKPBphtrY6Ob9lOFDHLgd355e0lw=; b=Y+mHHknOk99m7yJUgdSM5w83k9ExylQF2+4ZNqL1wg3DESl5c2D3s+qV5VQAzOWb8Md9mS 5RJYWYlrNfSKhXKmU7ZS4nvOqkc1/I3hd8+qup/HI3EtM9M7IYrzDcZ9Ku39xsETH9wyi5 U7y6K9kU6Wu9CYIAOUQQROR33Rvg7SY= 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 A291DA3B81; Mon, 26 Jul 2021 20:32:13 +0000 (UTC) Date: Mon, 26 Jul 2021 22:32:13 +0200 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , Dan Carpenter , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm: memcontrol: fix blocking rstat function called from atomic cgroup1 thresholding code Message-ID: References: <20210726150019.251820-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210726150019.251820-1-hannes@cmpxchg.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 26-07-21 11:00:19, Johannes Weiner wrote: > Dan Carpenter reports: > > The patch 2d146aa3aa84: "mm: memcontrol: switch to rstat" from Apr > 29, 2021, leads to the following static checker warning: > > kernel/cgroup/rstat.c:200 cgroup_rstat_flush() > warn: sleeping in atomic context > > mm/memcontrol.c > 3572 static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) > 3573 { > 3574 unsigned long val; > 3575 > 3576 if (mem_cgroup_is_root(memcg)) { > 3577 cgroup_rstat_flush(memcg->css.cgroup); > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > This is from static analysis and potentially a false positive. The > problem is that mem_cgroup_usage() is called from __mem_cgroup_threshold() > which holds an rcu_read_lock(). And the cgroup_rstat_flush() function > can sleep. > > 3578 val = memcg_page_state(memcg, NR_FILE_PAGES) + > 3579 memcg_page_state(memcg, NR_ANON_MAPPED); > 3580 if (swap) > 3581 val += memcg_page_state(memcg, MEMCG_SWAP); > 3582 } else { > 3583 if (!swap) > 3584 val = page_counter_read(&memcg->memory); > 3585 else > 3586 val = page_counter_read(&memcg->memsw); > 3587 } > 3588 return val; > 3589 } > > __mem_cgroup_threshold() indeed holds the rcu lock. In addition, the > thresholding code is invoked during stat changes, and those contexts > have irqs disabled as well. If the lock breaking occurs inside the > flush function, it will result in a sleep from an atomic context. > > Use the irsafe flushing variant in mem_cgroup_usage() to fix this. > > Fixes: 2d146aa3aa84 ("mm: memcontrol: switch to rstat") > Cc: > Reported-by: Dan Carpenter > Signed-off-by: Johannes Weiner Acked-by: Michal Hocko Thanks! > --- > mm/memcontrol.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index ae1f5d0cb581..eb8e87c4833f 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3574,7 +3574,8 @@ static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) > unsigned long val; > > if (mem_cgroup_is_root(memcg)) { > - cgroup_rstat_flush(memcg->css.cgroup); > + /* mem_cgroup_threshold() calls here from irqsafe context */ > + cgroup_rstat_flush_irqsafe(memcg->css.cgroup); > val = memcg_page_state(memcg, NR_FILE_PAGES) + > memcg_page_state(memcg, NR_ANON_MAPPED); > if (swap) > -- > 2.32.0 -- Michal Hocko SUSE Labs