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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 671A6C282CE for ; Mon, 11 Feb 2019 12:38:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3307421A80 for ; Mon, 11 Feb 2019 12:38:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=szeredi.hu header.i=@szeredi.hu header.b="n/TlEoQ8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727415AbfBKMh4 (ORCPT ); Mon, 11 Feb 2019 07:37:56 -0500 Received: from mail-it1-f194.google.com ([209.85.166.194]:55704 "EHLO mail-it1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727197AbfBKMh4 (ORCPT ); Mon, 11 Feb 2019 07:37:56 -0500 Received: by mail-it1-f194.google.com with SMTP id f18so14809732itb.5 for ; Mon, 11 Feb 2019 04:37:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=szeredi.hu; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=uNFH6w4Gy4uKEZhuZeiRBbvSCjujATtfuhBq8C9Cazs=; b=n/TlEoQ8bZb5eihGCfmnVh9pL0fX8MsMYeXoJ/NgIdo1ypegyOCVv2ox2G4oa1dg7m SL+lj6om4336eSDGaTnp7eOqeVOw1m/IKFjs3UP4scTZCRTF5Ko7kEflckxhpJXzWAYi 0l2LgVOymq8jhNvXvGZB/3JjlxdYmIJv3iVe8= 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=uNFH6w4Gy4uKEZhuZeiRBbvSCjujATtfuhBq8C9Cazs=; b=VaI6gPeAzFtrLSX8EJarh/qiSDyJEnBWqlBXlLzyLio+n/lZtzOpbaegsjF6WpOpNW az1eCI98Eebi9g1U66wgzW/JH/JjmRFbsn07arjKLUQBiWQnZ33Jk2iu+S15N5XjZd4C u0bxktnPVbXglAdsPJggpwAqE4w7YPYBjIAN9T7cjUJNl3+HSxuiDocdYCWTq5ArmspE nvbf4MiG1zDF8fGC01v3B6/Cj7pPStdI0vaucS3w1LvFmEMsl1vZq4bs4+oNNfyMM6oE hAP5Nkocb1DRJxfnInQlWOY8c/HbH+Pf6BFuz1OY5xb3MoEYDbwUIugL1ewJFEEv2brX 28fg== X-Gm-Message-State: AHQUAubPncwLaltkFqxRfSibPa0kPfFhhgwN9he0b2bqgg1x24FCT/3u aMViqsrCmCsYv7AGamW0syahZ5SnOZbtucuMHf2ong== X-Google-Smtp-Source: AHgI3IYZrRTvfHP2jioVTbQED+vu1rQusktbW3k95D+sx4H5VwRiK8Izt1SLFFl9c10umi55rLr3U6ixy7XeMw1DP60= X-Received: by 2002:a5e:d803:: with SMTP id l3mr13331687iok.144.1549888674884; Mon, 11 Feb 2019 04:37:54 -0800 (PST) MIME-Version: 1.0 References: <000000000000701c3305818e4814@google.com> In-Reply-To: From: Miklos Szeredi Date: Mon, 11 Feb 2019 13:37:43 +0100 Message-ID: Subject: Re: possible deadlock in pipe_lock (2) To: Amir Goldstein , Jan Kara Cc: 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 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? Thanks, Miklos