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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11CD1C678D4 for ; Wed, 1 Mar 2023 20:49:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229789AbjCAUs7 (ORCPT ); Wed, 1 Mar 2023 15:48:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229780AbjCAUsy (ORCPT ); Wed, 1 Mar 2023 15:48:54 -0500 Received: from mail-yw1-x112f.google.com (mail-yw1-x112f.google.com [IPv6:2607:f8b0:4864:20::112f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 272433D099 for ; Wed, 1 Mar 2023 12:48:50 -0800 (PST) Received: by mail-yw1-x112f.google.com with SMTP id 00721157ae682-536be69eadfso388765237b3.1 for ; Wed, 01 Mar 2023 12:48:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1677703729; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=pJ2NmEPepPcvJe3Ak3yvSzcJWQBbkK4dHDuYNukFsA4=; b=ZxKqVSfGUt6z5p9e4Sh1vteLyfGnKL+sAJJBJkTnttLJNPVFFrb6Q8lkW4nTVy/X2l N5/JO3+zD3LYuIc2tT3uQ9kIHFoLQRkCFwDLNeck6pX6qG69jf8xc79xIfmdgBxeS2ae gPO0iZxFqzN5e0MFXgXFukI6ZT1Qrza33kJHQMolayOC/Za+3ACrukE+LUqaukvDjFBr OCIs7/uvb4O8rRAJLPZcEaseFUhGWxhoiyvpdWyK/dTN0FhnoLz0yXoGm3A/ONfizmTE f5SPURgiWH8B09lMfmeWhs9AhcPquBUDJmmxlJq+e+o8001eO34zMlf4yk7u8TJKsluk F2zw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1677703729; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=pJ2NmEPepPcvJe3Ak3yvSzcJWQBbkK4dHDuYNukFsA4=; b=RFSbTFAbK2SE/LudVKzu+CXh2cAsXWbcUJckiOg0SzCB0lRGA0qoSAp6d4r/zcx7MT l5lsVKDmxHo+MZaRJwzR5Q77+G19JtMKnVDqGgtqMLE44seayPVPdM/wQiwK6PSBAP/z JSe/VSI+iavJ9FJZ4P+/alVBx3FgMfN0WUNnjuDJNRJqgGnyfW3oJyIFrLS8kD2vUTOi wPb4BM31DP705j0K1cU0UTOxhBgDfkttkToN2u4RNvBQ02+6pocttTbPV5K+1K1eFD6f 0ASlz3rot6+LguwQjUHIqybNMS263Uw6II3T1/Jh4GtpigRPuMU33Ag/hg8B7uja+S+5 OjMw== X-Gm-Message-State: AO0yUKW+ztxd8qTqVQyW7rVhJAxx0d+qGhnyThXiF/wivIjdzD5YbavZ MnCWA6L5fi5npY0NWt54+y9JOtLtoLst4fWf3p60Aw== X-Google-Smtp-Source: AK7set8e8aN8lhe1v2IkmF76VC5t9F6FyKK9q3rCkR0EKsJvTiU9L2roDVQILALGedIxz/crcfjfzcHKNZduJg/PH8w= X-Received: by 2002:a81:ad03:0:b0:530:bbd3:798b with SMTP id l3-20020a81ad03000000b00530bbd3798bmr4793692ywh.0.1677703729203; Wed, 01 Mar 2023 12:48:49 -0800 (PST) MIME-Version: 1.0 References: <20230301193403.1507484-1-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 1 Mar 2023 12:48:38 -0800 Message-ID: Subject: Re: [PATCH 1/1] psi: remove 500ms min window size limitation for triggers To: Johannes Weiner Cc: tj@kernel.org, lizefan.x@bytedance.com, peterz@infradead.org, johunt@akamai.com, mhocko@suse.com, keescook@chromium.org, quic_sudaraja@quicinc.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 1, 2023 at 12:07=E2=80=AFPM Johannes Weiner wrote: > > On Wed, Mar 01, 2023 at 11:34:03AM -0800, Suren Baghdasaryan wrote: > > Current 500ms min window size for psi triggers limits polling interval > > to 50ms to prevent polling threads from using too much cpu bandwidth by > > polling too frequently. However the number of cgroups with triggers is > > unlimited, so this protection can be defeated by creating multiple > > cgroups with psi triggers (triggers in each cgroup are served by a sing= le > > "psimon" kernel thread). > > Instead of limiting min polling period, which also limits the latency o= f > > psi events, it's better to limit psi trigger creation to authorized use= rs > > only, like we do for system-wide psi triggers (/proc/pressure/* files c= an > > be written only by processes with CAP_SYS_RESOURCE capability). This al= so > > makes access rules for cgroup psi files consistent with system-wide one= s. > > Add a CAP_SYS_RESOURCE capability check for cgroup psi file writers and > > remove the psi window min size limitation. > > > > Suggested-by: Sudarshan Rajagopalan > > Link: https://lore.kernel.org/all/cover.1676067791.git.quic_sudaraja@qu= icinc.com/ > > Signed-off-by: Suren Baghdasaryan > > --- > > kernel/cgroup/cgroup.c | 10 ++++++++++ > > kernel/sched/psi.c | 4 +--- > > 2 files changed, 11 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > > index 935e8121b21e..b600a6baaeca 100644 > > --- a/kernel/cgroup/cgroup.c > > +++ b/kernel/cgroup/cgroup.c > > @@ -3867,6 +3867,12 @@ static __poll_t cgroup_pressure_poll(struct kern= fs_open_file *of, > > return psi_trigger_poll(&ctx->psi.trigger, of->file, pt); > > } > > > > +static int cgroup_pressure_open(struct kernfs_open_file *of) > > +{ > > + return (of->file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOUR= CE)) ? > > + -EPERM : 0; > > +} > > I agree with the change, but it's a bit unfortunate that this check is > duplicated between system and cgroup. > > What do you think about psi_trigger_create() taking the file and > checking FMODE_WRITE and CAP_SYS_RESOURCE against file->f_cred? That's definitely doable and we don't even need to pass file to psi_trigger_create() since it's called only when we write to the file. However by moving the capability check into psi_trigger_create() we also postpone the check until write() instead of failing early in open(). I always assumed failing early is preferable but if consolidating the code here makes more sense then I can make the switch. Please let me know if you still prefer to move the check.