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 CAF15C433EF for ; Mon, 30 May 2022 17:14:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240574AbiE3ROy (ORCPT ); Mon, 30 May 2022 13:14:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234576AbiE3ROx (ORCPT ); Mon, 30 May 2022 13:14:53 -0400 Received: from kylie.crudebyte.com (kylie.crudebyte.com [5.189.157.229]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 43B3F427C4 for ; Mon, 30 May 2022 10:14:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=kylie; h=Content-Type:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Content-ID:Content-Description; bh=jMYehlB9aLUgQ1tstMwnwZ61QG62rksDqgFFcnCVQnw=; b=SxpdlH8dBDao2azwBPGR9+mrEN En4n+oBmoxWawuMZDsQr+06EOwQkYJffGfhbDibikM/ERYN8ckVsJN6vHrE+OaNxR356uQmSTb0+I VLB3AqCOCt6YYrBS3SPYsndOA9htD013UdvbbAcuDTm+DOy4LZQyTCovz6tJubDzlQXEul7X5MBa+ Vb3mFPHwe7pz/5OBl6sSpkLV9rZA7eIWlvfALjP1b0VkUCoFFxBLc/hMDEHR5Aw5dKTOxwSznlT0x EiPjleRqEf7w/sRaFmfi3F/Brqpg2MbtsAI/g649Bc24vYqhkXeT5exMQYHJIr5TKc/qlYhpOH4VR oVweRXI2fVeuCLEBV6dwmT5/71nWlz6zxPlMTLk9UJhnw0dZi0kK2GkpHjY36IgYZj3sRD+kIYqd8 lfNx4MVfYpS57tzcNrxqWPHBfB9OVFniPco3ENau3DfnTI06gMdD1XPsdedmmkrk8woubmwpaW7ey FNbOw7KHDQSMfVydSmu4Po3GAIjwptYKKSqX8c6Ix/Tfrx9fbtad94ggoCrpna0zTtDLgG6W2ykqD VbpfjokQ4yLm8w+AdaIWxQfpV1t5ij8xmLfFtuN2FSz+E/Vj75o8dy03x8FFIJL4ctpWbpIv7c+KO Ma6/dsUBmXi5glfzHffEi7vpWX7qHM6SElNFJdZhQ=; From: Christian Schoenebeck To: Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Tyler Hicks Cc: Jianyong Wu , v9fs-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/5] 9p: Fix refcounting during full path walks for fid lookups Date: Mon, 30 May 2022 19:14:43 +0200 Message-ID: <43525959.9j6oIFhYhY@silver> In-Reply-To: <20220527000003.355812-2-tyhicks@linux.microsoft.com> References: <20220527000003.355812-1-tyhicks@linux.microsoft.com> <20220527000003.355812-2-tyhicks@linux.microsoft.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Freitag, 27. Mai 2022 01:59:59 CEST Tyler Hicks wrote: > Decrement the refcount of the parent dentry's fid after walking > each path component during a full path walk for a lookup. Failure to do > so can lead to fids that are not clunked until the filesystem is > unmounted, as indicated by this warning: > > 9pnet: found fid 3 not clunked That explains why I saw so many fids not being clunked with recent Linux kernel versions while doing some 9p protocol debugging with QEMU recently. > The improper refcounting after walking resulted in open(2) returning > -EIO on any directories underneath the mount point when using the virtio > transport. When using the fd transport, there's no apparent issue until > the filesytem is unmounted and the warning above is emitted to the logs. Actually I never saw that open() = -EIO error. Do you have a reproducer? > In some cases, the user may not yet be attached to the filesystem and a > new root fid, associated with the user, is created and attached to the > root dentry before the full path walk is performed. Increment the new > root fid's refcount to two in that situation so that it can be safely > decremented to one after it is used for the walk operation. The new fid > will still be attached to the root dentry when > v9fs_fid_lookup_with_uid() returns so a final refcount of one is > correct/expected. > > Fixes: 6636b6dcc3db ("9p: add refcount to p9_fid struct") > Cc: stable@vger.kernel.org > Signed-off-by: Tyler Hicks > --- > fs/9p/fid.c | 17 +++++------------ > 1 file changed, 5 insertions(+), 12 deletions(-) > > diff --git a/fs/9p/fid.c b/fs/9p/fid.c > index 79df61fe0e59..5a469b79c1ee 100644 > --- a/fs/9p/fid.c > +++ b/fs/9p/fid.c > @@ -152,7 +152,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct > dentry *dentry, const unsigned char **wnames, *uname; > int i, n, l, clone, access; > struct v9fs_session_info *v9ses; > - struct p9_fid *fid, *old_fid = NULL; > + struct p9_fid *fid, *old_fid; > > v9ses = v9fs_dentry2v9ses(dentry); > access = v9ses->flags & V9FS_ACCESS_MASK; > @@ -194,13 +194,12 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct > dentry *dentry, if (IS_ERR(fid)) > return fid; > > + refcount_inc(&fid->count); > v9fs_fid_add(dentry->d_sb->s_root, fid); > } > /* If we are root ourself just return that */ > - if (dentry->d_sb->s_root == dentry) { > - refcount_inc(&fid->count); > + if (dentry->d_sb->s_root == dentry) > return fid; > - } Hmm, wouldn't it then be possible that the root fid is returned with refcount being 2 here? > /* > * Do a multipath walk with attached root. > * When walking parent we need to make sure we > @@ -212,6 +211,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct > dentry *dentry, fid = ERR_PTR(n); > goto err_out; > } > + old_fid = fid; > clone = 1; > i = 0; > while (i < n) { > @@ -221,15 +221,8 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct > dentry *dentry, * walk to ensure none of the patch component change > */ > fid = p9_client_walk(fid, l, &wnames[i], clone); > + p9_client_clunk(old_fid); > if (IS_ERR(fid)) { > - if (old_fid) { > - /* > - * If we fail, clunk fid which are mapping > - * to path component and not the last component > - * of the path. > - */ > - p9_client_clunk(old_fid); > - } > kfree(wnames); > goto err_out; > } So this is the actual fix mentioned in the commit log. Makes sense. Nitpicking: Wouldn't it be a bit cleaner to set old_fid solely within the while loop and just before overwriting fid? And as we now have bumped to -std=C11, probably making old_fid a local variable within loop scope only? Best regards, Christian Schoenebeck