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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 0CFD3C433DB for ; Wed, 20 Jan 2021 06:54:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BEEAD2313C for ; Wed, 20 Jan 2021 06:54:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727794AbhATGyD (ORCPT ); Wed, 20 Jan 2021 01:54:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39772 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726590AbhATGxa (ORCPT ); Wed, 20 Jan 2021 01:53:30 -0500 Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3472DC0613D3 for ; Tue, 19 Jan 2021 22:52:50 -0800 (PST) Received: by mail-ed1-x536.google.com with SMTP id bx12so10445802edb.8 for ; Tue, 19 Jan 2021 22:52:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=OUwyk7xtJXT5NiDavD07ZTFekT45AnyTwd1+tu8BV2s=; b=pnwim4oCTPJUkeAUxNAT5zomyWF/8LBZ1cr/prJSrtoyHr6HXwRulATLeGbM/zO+Ds iqSkBnm5FA9GpCYr9mahnXVLdDvm3bdZX5GeRjmIUXWkd0oW4aY7i0dX6thJBZ3mMVSV kWWzYR0S87bDJHTos/rkGTLnwTAx9SG+OZRig4PiWcIGWCrfXuJmOjX0DzJnInkNrP35 pB4N6RKJdbQJV87bfF3r/Bm8NHvVpa5erF24fOAXjjbO5h7EtqLSRTdmt2rPNoqOJQ/v xZ5GndPVEXc7GmGALiHmeXTnM/YhXGYk4iKYyiuWGdXGm8MYsZHmPZawRrhsinkdASfM xHOw== 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:content-transfer-encoding; bh=OUwyk7xtJXT5NiDavD07ZTFekT45AnyTwd1+tu8BV2s=; b=ZbCUhGbEpenzTPbXCBh6VF4BBoDiRwU9OfejyqAuSpTU+2RUos6aeJAenDbTwhAwdk +nfxDwD1Dese7FBODgIFZWUjb48emdtvEfmxZ/fMj/6R5L0zmXFMLtlf7VWPh0qRcwce Wd9AqyXne6rEn9nJV4kGG8b/ibRuXPsPDjAAXRejJVpsDYD+1oBCV9uPAbhYWUHKtd0c hUMghq2EsLcuFG3uczkNLSY0CZ48jvr4xsi6LJFcYpQhhj2fLlImafamMbkf6u/LGE3e dktNP3S3c2uYHb3z93gfJ0f7mZlI05dySP9DPXdYiZux1AXVPCxw2GfzjpfXo1sBAu9r MaSA== X-Gm-Message-State: AOAM5307jwwUmp9bmRu0vIH6A7oZzg9hsQMDWbGqeQhy8EIykRptuREO uYuJLfZeOb+XzMHQ19OBOwWQV9l+dapvBA9eWVVH X-Google-Smtp-Source: ABdhPJz8mSZjfHOOyqb5onfPHShDdIVRGCg/2N4z9UKpZS1PnUlAPw4lgExHz6G+gVcVSgVIvukJvyXD7wAAibCHYOw= X-Received: by 2002:a05:6402:407:: with SMTP id q7mr6214637edv.312.1611125568895; Tue, 19 Jan 2021 22:52:48 -0800 (PST) MIME-Version: 1.0 References: <20210119045920.447-1-xieyongji@bytedance.com> <20210119045920.447-2-xieyongji@bytedance.com> In-Reply-To: From: Yongji Xie Date: Wed, 20 Jan 2021 14:52:38 +0800 Message-ID: Subject: Re: Re: [RFC v3 01/11] eventfd: track eventfd_signal() recursion depth separately in different cases To: Jason Wang Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , sgarzare@redhat.com, Parav Pandit , Bob Liu , Christoph Hellwig , Randy Dunlap , Matthew Wilcox , viro@zeniv.linux.org.uk, axboe@kernel.dk, bcrl@kvack.org, Jonathan Corbet , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Jan 20, 2021 at 12:24 PM Jason Wang wrote: > > > On 2021/1/19 =E4=B8=8B=E5=8D=8812:59, Xie Yongji wrote: > > Now we have a global percpu counter to limit the recursion depth > > of eventfd_signal(). This can avoid deadlock or stack overflow. > > But in stack overflow case, it should be OK to increase the > > recursion depth if needed. So we add a percpu counter in eventfd_ctx > > to limit the recursion depth for deadlock case. Then it could be > > fine to increase the global percpu counter later. > > > I wonder whether or not it's worth to introduce percpu for each eventfd. > > How about simply check if eventfd_signal_count() is greater than 2? > It can't avoid deadlock in this way. So we need a percpu counter for each eventfd to limit the recursion depth for deadlock cases. And using a global percpu counter to avoid stack overflow. Thanks, Yongji