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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E27AFC7EE23 for ; Fri, 24 Feb 2023 16:19:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229643AbjBXQTl (ORCPT ); Fri, 24 Feb 2023 11:19:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229470AbjBXQTj (ORCPT ); Fri, 24 Feb 2023 11:19:39 -0500 Received: from mail-yw1-x1132.google.com (mail-yw1-x1132.google.com [IPv6:2607:f8b0:4864:20::1132]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 56E3F63DE7 for ; Fri, 24 Feb 2023 08:19:36 -0800 (PST) Received: by mail-yw1-x1132.google.com with SMTP id 00721157ae682-53852143afcso150173737b3.3 for ; Fri, 24 Feb 2023 08:19:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=to:subject:message-id:date:from:in-reply-to:references:mime-version :from:to:cc:subject:date:message-id:reply-to; bh=XUu8O9ItgO5lYwAtPHJHsJmnXPyKxsMIFXboHJZ1WiA=; b=bk+XKHvYluEqedo5GNDcY5RMTQ/o8N2s2BzE4gdyRKU3AyNMW8c39fejODmXHLCTrx fU4/cTplkH4RALGpU5wQHfFjLhMRRisbS3dGlCEi/jjmE3nJqWQOBHNSQrOHBELrZdCh i8jxDrm/dfAZcHw/D3VeK2VxgvTxrGFlFlO+BaCDghsSidbxzNp0yXNy4evBpYLBBi7S wWWifr4z+uquUtm6qYZ8qP432cXNqXgI2pfu0iihAbeAPefZaiOQs+0iHm1c53TqUJ8p FkYhdSxsKN5PeKBYo8xtEFGZ+7wYyEUhq4BNEAdW5RyacNXoX7BO6Ax19uPcSSiUzET9 tYGA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=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=XUu8O9ItgO5lYwAtPHJHsJmnXPyKxsMIFXboHJZ1WiA=; b=o2QZWt4AtUSHrDIwL4ev3/6zzhNWUlFQS0fIp6PrW0rwsu9kX+5l0CNe6wdcM7YE9u Wn9s4y2GCCfMjhVvxNtdiKYvlNvereSMzD8BGgJNdEe8TfMO5CbQT47qVaNhfcntky/B wOfkbxFKEko8cAiMooGD4AnA6DjmtaaaUNdLFfauX0e+49W3029XJGRbJyv8i7sGmvid a3IRXuR5cfz9W6d/JaZtC9AqnZMxUakjflV7OJ/tSC1i9deknGYz+TgoQdaadbbp1r/4 MT+BrYhpG+Xp1QoTjwQt+3T/HDz85lcLRzsT1+9YwMnPRVILuPEGpPDlCRJJCajBGtQE uwaQ== X-Gm-Message-State: AO0yUKWFRTd+5NhhM+GyIFB/Z8Dqd7Qxt7cYU/p6GJtzLGFfOxG4vUdk e/XhOe8hhLOP7Y+lxgUsoKv6FQ/vggKiAZsDVxo0dw== X-Google-Smtp-Source: AK7set8+hWMLQ20WrNcIcseQyw5OXb1klKUHQhtiZRsS+K4K/AoKCdMeadKX1IN3ZbVuzdbUFFkiDaLVzuEYZYSy7i0= X-Received: by 2002:a05:6902:15cf:b0:8fc:686c:cf87 with SMTP id l15-20020a05690215cf00b008fc686ccf87mr178667ybu.4.1677255575272; Fri, 24 Feb 2023 08:19:35 -0800 (PST) MIME-Version: 1.0 References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-18-surenb@google.com> <20230223202011.dahh6cidqxhzoxne@revolver> <20230223202844.noant5suylne3dnh@revolver> <20230224014624.gnirnx625ylhoevb@revolver> <20230224161402.o7phj2crnt2xg4nl@revolver> In-Reply-To: <20230224161402.o7phj2crnt2xg4nl@revolver> From: Suren Baghdasaryan Date: Fri, 24 Feb 2023 08:19:24 -0800 Message-ID: Subject: Re: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or expanding it To: "Liam R. Howlett" , Suren Baghdasaryan , akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, michalechner92@googlemail.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 24, 2023 at 8:14 AM Liam R. Howlett wrote: > > * Suren Baghdasaryan [230223 21:06]: > > On Thu, Feb 23, 2023 at 5:46 PM Liam R. Howlett wrote: > > > > > > * Suren Baghdasaryan [230223 16:16]: > > > > On Thu, Feb 23, 2023 at 12:28 PM Liam R. Howlett > > > > wrote: > > > > > > > > > > > > > > > Wait, I figured a better place to do this. > > > > > > > > > > init_multi_vma_prep() should vma_start_write() on any VMA that is passed > > > > > in.. that we we catch any modifications here & in vma_merge(), which I > > > > > think is missed in this patch set? > > > > > > > > Hmm. That looks like a good idea but in that case, why not do the > > > > locking inside vma_prepare() itself? From the description of that > > > > function it sounds like it was designed to acquire locks before VMA > > > > modifications, so would be the ideal location for doing that. WDYT? > > > > > > That might be even better. I think it will result in even less code. > > > > Yes. > > > > > > > > There is also a vma_complete() which might work to call > > > vma_end_write_all() as well? > > > > If there are other VMAs already locked before vma_prepare() then we > > would unlock them too. Safer to just let mmap_unlock do > > vma_end_write_all(). > > > > > > > > > The only concern is vma_adjust_trans_huge() being called before > > > > vma_prepare() but I *think* that's safe because > > > > vma_adjust_trans_huge() does its modifications after acquiring PTL > > > > lock, which page fault handlers also have to take. Does that sound > > > > right? > > > > > > I am not sure. We are certainly safe the way it is, and the PTL has to > > > be safe for concurrent faults.. but this could alter the walk to a page > > > table while that walk is occurring and I don't think that happens today. > > > > > > It might be best to leave the locking order the way you have it, unless > > > someone can tell us it's safe? > > > > Yes, I have the same feelings about changing this. > > > > > > > > We could pass through the three extra variables that are needed to move > > > the vma_adjust_trans_huge() call within that function as well? This > > > would have the added benefit of having all locking grouped in the one > > > location, but the argument list would be getting long, however we could > > > use the struct. > > > > Any issues if I change the order to have vma_prepare() called always > > before vma_adjust_trans_huge()? That way the VMA will always be locked > > before vma_adjust_trans_huge() executes and we don't need any > > additional arguments. > > I preserved the locking order from __vma_adjust() to ensure there was no > issues. > > I am not sure but, looking through the page table information [1], it > seems that vma_adjust_trans_huge() uses the pmd lock, which is part of > the split page table lock. According to the comment in rmap, it should > be fine to reverse the ordering here. > > Instead of: > > mmap_lock() > vma_adjust_trans_huge() > pte_lock > pte_unlock > > vma_prepare() > mapping->i_mmap_rwsem lock > anon_vma->rwsem lock > > > > vma_complete() > anon_vma->rwsem unlock > mapping->i_mmap_rwsem unlock > > mmap_unlock() > > --------- > > We would have: > > mmap_lock() > vma_prepare() > mapping->i_mmap_rwsem lock > anon_vma->rwsem lock > > vma_adjust_trans_huge() > pte_lock > pte_unlock > > > > vma_complete() > anon_vma->rwsem unlock > mapping->i_mmap_rwsem unlock > > mmap_unlock() > > > Essentially, increasing the nesting of the pte lock, but not violating > the ordering. > > 1. https://docs.kernel.org/mm/split_page_table_lock.html Thanks for the confirmation, Liam. I'll make the changes and test over the weekend. If everything's still fine, I will post the next version with these and other requested changes on Monday. > > > > > > > > > remove & remove2 should be be detached in vma_prepare() or > > > vma_complete() as well? > > > > They are marked detached in vma_complete() (see > > https://lore.kernel.org/all/20230216051750.3125598-25-surenb@google.com/) > > and that should be enough. We should be safe as long as we mark them > > detached before unlocking the VMA. > > > > Right, Thanks. > > ... > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >