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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 199B5C433B4 for ; Sat, 3 Apr 2021 01:31:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF5F261168 for ; Sat, 3 Apr 2021 01:31:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235788AbhDCBbD (ORCPT ); Fri, 2 Apr 2021 21:31:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234488AbhDCBbC (ORCPT ); Fri, 2 Apr 2021 21:31:02 -0400 Received: from mail-qt1-x830.google.com (mail-qt1-x830.google.com [IPv6:2607:f8b0:4864:20::830]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3102C0613E6 for ; Fri, 2 Apr 2021 18:31:00 -0700 (PDT) Received: by mail-qt1-x830.google.com with SMTP id f12so240271qtf.2 for ; Fri, 02 Apr 2021 18:31:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=9JHlNTCSKPYkPHrzVLO9kGXjpVBrIBz8nNq/De5MvCQ=; b=d7ko8MH+3BuL+ciOLlWbGd7DaIVJy1K77TLGQENN9dJgY2R5RJQIUlw7+x7/YEX2TD /21cXKw0dX/xCxocMhrmPF5NrkK2q3VNh3JckN2DlPRtPAi3IiQdMCA+oTCDT7wnM+fI K1AHYGBj/Pe8jkLhCvI/LSVIaw1Hm5VmXJpAqx9J1CqwN/KHwtx/gvuk3Sdv7c2862Qi z58k0J+ULoJopfR8UC8qznd8sBgSUJJNf5OCRl3nU0bg4XmbY886y3ykXwAOiwl1I2Kf kqHaVIGBybsA+rj05KkEtmNUVupfFvv34NotM/X+XyfCp40e4USpk4f+RFKCY+5vnEta ZJmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=9JHlNTCSKPYkPHrzVLO9kGXjpVBrIBz8nNq/De5MvCQ=; b=dp4Y3/CVUP2QNrRMaZ3KmluRimHCLWtOo8GV2X6wcycUqOEkw6A11YjsjnQDtchlWR f3zRPupV0J5sjw+MyI/nlC94aKC+Z3QDSNx49l9WoQ23MVDj76FQIOmdwUm6v3ObM7zd 0q3lQTUvLDd0KNxZWXwPJNFDsCdo2FRvVlunJVi6qjSWtAwunbYRvPUR+a1KpafK/t1O OAHaVIAYfT9XrEGhC05osTW2F5pk3SYafxuAZCcyMFvULdcSjsMCtipE1DhkBb17Urwh oGOHdf59MTc0jE26p3FwHiklaoyyqLDwG2/FfuX9v1fR7NNrwH2TMX/2pUF89hknrM3l j1AQ== X-Gm-Message-State: AOAM532HgPcvumqX2BZen2jjyGxyjyWY/NNY4HQX6/mmkgnXJtW1EqVx Q3u21T9BbmyOEkBzsL//LAZPpSSZNaKQDKA5yBq76A== X-Google-Smtp-Source: ABdhPJz1k9d1fbbJ4r2iaVShs5FXuhTsbDFXMm272iJ+XTqfG34UKWXe5ENW0mUWHp6kI9U+fhepoEbGRZIQaicLDrg= X-Received: by 2002:a05:622a:114:: with SMTP id u20mr13559973qtw.317.1617413459565; Fri, 02 Apr 2021 18:30:59 -0700 (PDT) MIME-Version: 1.0 References: <20210401131012.395311786@infradead.org> <20210401133917.590280797@infradead.org> In-Reply-To: <20210401133917.590280797@infradead.org> From: Josh Don Date: Fri, 2 Apr 2021 18:30:48 -0700 Message-ID: Subject: Re: [PATCH 9/9] sched: prctl() and cgroup interaction To: Peter Zijlstra Cc: Joel Fernandes , "Hyser,Chris" , Ingo Molnar , Vincent Guittot , Valentin Schneider , Mel Gorman , linux-kernel , Tejun Heo , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, I walked through the reference counting, and it seems good to me (though it did take a few passes to fully digest the invariants for the fat cookie stuff). > +unsigned long sched_core_alloc_cookie(unsigned int type) > { > struct sched_core_cookie *ck = kmalloc(sizeof(*ck), GFP_KERNEL); > if (!ck) > return 0; > - refcount_set(&ck->refcnt, 1); > + WARN_ON_ONCE(type > GROUP_COOKIE); > + sched_core_init_cookie(ck, type); > sched_core_get(); > > - return (unsigned long)ck; > + return (unsigned long)ck | type; > } This feels like it needs to be stronger than a WARN_ON_ONCE; could create a corrupted address that we later try to kfree(). Also, for my own edification, why will the bottom two bits here always be 0? > -unsigned long sched_core_alloc_cookie(void) > +static inline void *cookie_ptr(unsigned long cookie) > +{ > + return (void *)(cookie & ~3UL); > +} > + > +static inline int cookie_type(unsigned long cookie) > +{ > + return cookie & 3; > +} s/3/FAT_COOKIE > +#define FAT_COOKIE 0x03 Move to sched.h to group with TASK/GROUP_COOKIE? > +static unsigned long __sched_core_fat_cookie(struct task_struct *p, > + void **spare_fat, > + unsigned long cookie) > +{ This function looks good to me, but could use some more comments about the pre/post-condition assumptions. Ie. cookie already has a get() associated with it, caller is expected to kfree the spare_fat. > + raw_spin_lock_irqsave(&fat_lock, flags); > + n = rb_find_add(&fat->node, &fat_root, fat_cmp); > + raw_spin_unlock_irqrestore(&fat_lock, flags); > + > + if (n) { > + sched_core_put_fat(fat); > + fat = node_2_fat(n); This put() doesn't seem strictly necessary; caller will be unconditionally freeing the spare_fat. Keep anyway for completeness, but add a comment?