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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 AB2E5C169C4 for ; Mon, 11 Feb 2019 13:08:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 741E120818 for ; Mon, 11 Feb 2019 13:08:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="eickXS0P" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727608AbfBKNIO (ORCPT ); Mon, 11 Feb 2019 08:08:14 -0500 Received: from mail-yw1-f68.google.com ([209.85.161.68]:45602 "EHLO mail-yw1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726025AbfBKNIO (ORCPT ); Mon, 11 Feb 2019 08:08:14 -0500 Received: by mail-yw1-f68.google.com with SMTP id d190so4122095ywd.12; Mon, 11 Feb 2019 05:08:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=a6gP1nxweVNamMHo13Xt13dUc8s463gbzDwu4nEPUCc=; b=eickXS0P0Oi2eR/vu8HMvWXFAHCSS/hH7ohEiYSEeHDtmJkpqgibHgzLI22X0hKj+s eWt5YcX8GTQrSb+MFA51MZ0V0Dj3mjI9Td9TNdV9bdYhbtwjIVcBih0ElY2fY2KKB79q M45BxpYrTOO2vuQjotx+sqjU+k7bBXK3fbjvboFDSlE4G6tXVbwm6ezQHk7CqJYDna1Z Jzb1kWviyaLTq8x/lTTjhjf4j08cB2M1yl3mozbZi+JHHn6bTSajJetvFlrqHZmI0Kjk V1rRiXC4R0br+Qm6EajtrGpxupmT/5eWvC08OMQ4UoWOrEPig6jNx6cOWqZ5wRNSsBa9 pH8A== 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=a6gP1nxweVNamMHo13Xt13dUc8s463gbzDwu4nEPUCc=; b=nkWAgR0CmeCJX07JWjcNdlFaudL+F1Kt2cWPPV79Q/B87a4WubiTlOKq+9E2P0wwFv tF5BbxFhNlNtk9WKCusKYghx+p/snNV3xDc0nOsC9AKVGUW5JOiZMqWSae3lOwBFgzml uQhdKQOtB5AU4igsGohpvDFVfLZ/muIvP37EJNLLt5/HGd6qWmhTr+cqtEWzOOWRLiqu T1PtN6KkrmxDyN3xsjdDU7h4CgiXfQQTEygIy9v54f7WfV+oKFd8zbiSfi21pZWuDcjI IfAAJyjHm2x+eZeQIYNXHmsK6SdevgN32413Bl8UEn800XKFOTAyCsMBQghppqNcrPJx EciQ== X-Gm-Message-State: AHQUAuY75xLip73bfPFQl2V6OrngUuLXNmmrr8cxvXAtwlpGsXF4/Z1Y jj02QvMPPmVCC8PR1kkJOiPiP5HpEtjgwlBTbRw= X-Google-Smtp-Source: AHgI3IYamxTS6n3At0IR8R8gCmkIV16zLL3IuO7sK6fbS6TkDM+F3RgAgfrCP4tmiZvbO3cK9Ds+UM5Cd3MBWcFz/6k= X-Received: by 2002:a81:1b4b:: with SMTP id b72mr7247973ywb.211.1549890492718; Mon, 11 Feb 2019 05:08:12 -0800 (PST) MIME-Version: 1.0 References: <000000000000701c3305818e4814@google.com> In-Reply-To: From: Amir Goldstein Date: Mon, 11 Feb 2019 15:08:01 +0200 Message-ID: Subject: Re: possible deadlock in pipe_lock (2) To: Miklos Szeredi Cc: Jan Kara , linux-fsdevel , linux-kernel , syzkaller-bugs@googlegroups.com, Al Viro , syzbot , overlayfs Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Feb 11, 2019 at 2:37 PM Miklos Szeredi wrote: > > On Mon, Feb 11, 2019 at 1:06 PM Miklos Szeredi wrote: > > > > On Mon, Feb 11, 2019 at 8:38 AM Amir Goldstein wrote: > > > > > > On Sun, Feb 10, 2019 at 8:23 PM syzbot > > > wrote: > > > > > > -> #1 (&ovl_i_mutex_key[depth]){+.+.}: > > > > down_write+0x38/0x90 kernel/locking/rwsem.c:70 > > > > inode_lock include/linux/fs.h:757 [inline] > > > > ovl_write_iter+0x148/0xc20 fs/overlayfs/file.c:231 > > > > call_write_iter include/linux/fs.h:1863 [inline] > > > > new_sync_write fs/read_write.c:474 [inline] > > > > __vfs_write+0x613/0x8e0 fs/read_write.c:487 > > > > kobject: 'loop4' (000000009e2b886d): kobject_uevent_env > > > > __kernel_write+0x110/0x3b0 fs/read_write.c:506 > > > > write_pipe_buf+0x15d/0x1f0 fs/splice.c:797 > > > > splice_from_pipe_feed fs/splice.c:503 [inline] > > > > __splice_from_pipe+0x39a/0x7e0 fs/splice.c:627 > > > > splice_from_pipe+0x108/0x170 fs/splice.c:662 > > > > default_file_splice_write+0x3c/0x90 fs/splice.c:809 > > > > Irrelevant to the lockdep splat, but why isn't there an > > ovl_splice_write() that just recurses into realfile->splice_write()? > > Sounds like a much more efficient way to handle splice read and > > write... > > > > [...] > > > > > Miklos, > > > > > > Its good that this report popped up again, because I went to > > > look back at my notes from previous report [1]. > > > If I was right in my previous analysis then we must have a real > > > deadlock in current "lazy copy up" WIP patches. Right? > > > > Hmm, AFAICS this circular dependency translated into layman's terms: > > > > pipe lock -> ovl inode lock (splice to ovl file) > > > > ovl inode lock -> upper freeze lock (truncate of ovl file) > > > > upper freeze lock -> pipe lock (splice to upper file) > > So what can we do with this? > > The "freeze lock -> inode lock" dependency is fixed. This is > reversed in overlay to "ovl inode lock -> upper freeze lock", which is > okay, because this is a nesting that cannot be reversed. But in > splice the pipe locks comes in between: "freeze lock -> pipe lock -> > inode lock" which breaks this nesting direction and creates a true > reverse dependency between ovl inode lock and upper freeze lock. > > The only way I see this could be fixed is to move the freeze lock > inside the pipe lock. But that would mean splice/sendfile/etc could > be frozen with the pipe lock held. It doesn't look nice. > > Any other ideas? > [CC Jan] I think we are allowed to file_start_write_trylock(upper) before ovl_inode_lock(). This in ONLY needed to cover the corner case of upper being frozen in between "upper freeze lock -> pipe lock" and thread B being in between "ovl inode lock -> upper freeze lock". Is it OK to return a transient error in this corner copy up case? Thanks, Amir.