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=-20.6 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 492ECC433E0 for ; Thu, 30 Jul 2020 19:26:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 21E2A2072A for ; Thu, 30 Jul 2020 19:26:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="gj5uH8D4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730548AbgG3T0l (ORCPT ); Thu, 30 Jul 2020 15:26:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44574 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726581AbgG3T0j (ORCPT ); Thu, 30 Jul 2020 15:26:39 -0400 Received: from mail-qk1-x749.google.com (mail-qk1-x749.google.com [IPv6:2607:f8b0:4864:20::749]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EC177C061575 for ; Thu, 30 Jul 2020 12:26:38 -0700 (PDT) Received: by mail-qk1-x749.google.com with SMTP id d131so19352354qke.3 for ; Thu, 30 Jul 2020 12:26:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=fWc6OJCig1UgfvHtWplz+nD9vozoDKzNVIvYHPTkg44=; b=gj5uH8D4Swjos7n2MMJejn1TAY3/L82VroaxdW/TCkIJ79VyK0QF+7je5BWTh2VdbP S5EJcY/69Oah1CX+JxuEJQFQiERjk/P36vSs5VY/IAzzXXFTcElypDb5ad2LCfKgg07p bxmXzb+N1u0FJ/kmrnEpOysUXavSYtx5LY2CqEkI9v108NbkONilghGgiQFXGU6ZnOQS tV4PACfZgq/MYzgVSxp7OsSRh4PVZC9+HRmf49Eutm2q6iUHcHMvbPFTIqgYorCXg0F3 6Rxksb9qwD2MmW8j0Y9pUDSrTzgxYA1mNCTFcqttpvKe9S03LbVAvGFse0CBzYiYrZDF 25FQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=fWc6OJCig1UgfvHtWplz+nD9vozoDKzNVIvYHPTkg44=; b=Yl7EUcjG6/pZF42RwEc8MCwtdkVPWBfI7TGTzowWnwmi2W837KcvPNSgLvukoOm/kG /6fK8sjev0Y8O2iqpBygfzv98UrJXbI01OASIiKU/I0/c3cyHLcg34gkUJkdm982Tk2w HFAe798T7vP7vReOYgc5aw/nOhAs4nc4Ctn1W7SXSuR0mJmzwDAKe6LfCv0kB4fMvEZN /bpDuPv5aPBczH/fDpHYJ9wdr/m8fDJQGPFbw5GhHks1HVybzYBrT4rkEVBzP8+186H/ YzJ1j7e9dIdkKMZkOtaNSQjiq4IxgZehYHl8aQ9GOFQlWoHbb4EPvkp9Moloc+tKob9V 9FIg== X-Gm-Message-State: AOAM530s4yir5lE8ZP8Yaajg+mn0pJUitLl+i9YzHwDxNIzonexLFSNY RnENBfCseJPxNC/M3jUlv9tpj+a9YA8= X-Google-Smtp-Source: ABdhPJzEMZe4ramJ8Ov7HBdblAvH3a+W031fHCnG32znIrk4AscZJPDQJ3jlVI/1fwnUZWE1mXm5diLdqiM= X-Received: by 2002:ad4:40cb:: with SMTP id x11mr702214qvp.176.1596137197459; Thu, 30 Jul 2020 12:26:37 -0700 (PDT) Date: Thu, 30 Jul 2020 12:26:32 -0700 Message-Id: <20200730192632.3088194-1-surenb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.163.g6104cc2f0b6-goog Subject: [PATCH v2 1/1] staging: android: ashmem: Fix lockdep warning for write operation From: Suren Baghdasaryan To: surenb@google.com Cc: gregkh@linuxfoundation.org, arve@android.com, tkjos@android.com, maco@android.com, joel@joelfernandes.org, christian@brauner.io, hridya@google.com, mhocko@kernel.org, hdanton@sina.com, ebiggers@kernel.org, devel@driverdev.osuosl.org, linux-mm@kvack.org, stable@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com, syzbot+7a0d9d0b26efefe61780@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org syzbot report [1] describes a deadlock when write operation against an ashmem fd executed at the time when ashmem is shrinking its cache results in the following lock sequence: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(&sb->s_type->i_mutex_key#13); lock(fs_reclaim); lock(&sb->s_type->i_mutex_key#13); kswapd takes fs_reclaim and then inode_lock while generic_perform_write takes inode_lock and then fs_reclaim. However ashmem does not support writing into backing shmem with a write syscall. The only way to change its content is to mmap it and operate on mapped memory. Therefore the race that lockdep is warning about is not valid. Resolve this by introducing a separate lockdep class for the backing shmem inodes. [1]: https://lkml.kernel.org/lkml/0000000000000b5f9d059aa2037f@google.com/ Reported-by: syzbot+7a0d9d0b26efefe61780@syzkaller.appspotmail.com Signed-off-by: Suren Baghdasaryan Reviewed-by: Joel Fernandes (Google) --- drivers/staging/android/ashmem.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index c05a214191da..10b4be1f3e78 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -95,6 +95,15 @@ static DEFINE_MUTEX(ashmem_mutex); static struct kmem_cache *ashmem_area_cachep __read_mostly; static struct kmem_cache *ashmem_range_cachep __read_mostly; +/* + * A separate lockdep class for the backing shmem inodes to resolve the lockdep + * warning about the race between kswapd taking fs_reclaim before inode_lock + * and write syscall taking inode_lock and then fs_reclaim. + * Note that such race is impossible because ashmem does not support write + * syscalls operating on the backing shmem. + */ +static struct lock_class_key backing_shmem_inode_class; + static inline unsigned long range_size(struct ashmem_range *range) { return range->pgend - range->pgstart + 1; @@ -396,6 +405,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) if (!asma->file) { char *name = ASHMEM_NAME_DEF; struct file *vmfile; + struct inode *inode; if (asma->name[ASHMEM_NAME_PREFIX_LEN] != '\0') name = asma->name; @@ -407,6 +417,8 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) goto out; } vmfile->f_mode |= FMODE_LSEEK; + inode = file_inode(vmfile); + lockdep_set_class(&inode->i_rwsem, &backing_shmem_inode_class); asma->file = vmfile; /* * override mmap operation of the vmfile so that it can't be -- 2.28.0.163.g6104cc2f0b6-goog