From: Gao Xiang <hsiangkao@aol.com> To: Eric Biggers <ebiggers@kernel.org> Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Alexander Viro <viro@zeniv.linux.org.uk>, Daniel Rosenberg <drosen@google.com>, Gabriel Krisman Bertazi <krisman@collabora.com> Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Date: Fri, 24 Jan 2020 13:27:50 +0800 [thread overview] Message-ID: <20200124052740.GB31271@hsiangkao-HP-ZHAN-66-Pro-G1> (raw) In-Reply-To: <20200124051601.GB832@sol.localdomain> On Thu, Jan 23, 2020 at 09:16:01PM -0800, Eric Biggers wrote: > On Fri, Jan 24, 2020 at 01:04:25PM +0800, Gao Xiang wrote: > > > diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c > > > index 8964778aabefb..0129d14629881 100644 > > > --- a/fs/ext4/dir.c > > > +++ b/fs/ext4/dir.c > > > @@ -671,9 +671,11 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len, > > > const char *str, const struct qstr *name) > > > { > > > struct qstr qstr = {.name = str, .len = len }; > > > - struct inode *inode = dentry->d_parent->d_inode; > > > + const struct dentry *parent = READ_ONCE(dentry->d_parent); > > > > I'm not sure if we really need READ_ONCE d_parent here (p.s. d_parent > > won't be NULL anyway), and d_seq will guard all its validity. If I'm > > wrong, correct me kindly... > > > > Otherwise, it looks good to me... > > Reviewed-by: Gao Xiang <gaoxiang25@huawei.com> > > > > While d_parent can't be set to NULL, it can still be changed concurrently. > So we need READ_ONCE() to ensure that a consistent value is used. If I understand correctly, unlazy RCU->ref-walk will be guarded by seqlock, and for ref-walk we have d_lock (and even parent lock) in relative paths. So I prematurely think no race of renaming or unlinking evenually. I'm curious about that if experts could correct me about this. Thanks, Gao Xiang > > - Eric
WARNING: multiple messages have this Message-ID (diff)
From: Gao Xiang via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net> To: Eric Biggers <ebiggers@kernel.org> Cc: Daniel Rosenberg <drosen@google.com>, linux-f2fs-devel@lists.sourceforge.net, Alexander Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Gabriel Krisman Bertazi <krisman@collabora.com> Subject: Re: [f2fs-dev] [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Date: Fri, 24 Jan 2020 13:27:50 +0800 [thread overview] Message-ID: <20200124052740.GB31271@hsiangkao-HP-ZHAN-66-Pro-G1> (raw) In-Reply-To: <20200124051601.GB832@sol.localdomain> On Thu, Jan 23, 2020 at 09:16:01PM -0800, Eric Biggers wrote: > On Fri, Jan 24, 2020 at 01:04:25PM +0800, Gao Xiang wrote: > > > diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c > > > index 8964778aabefb..0129d14629881 100644 > > > --- a/fs/ext4/dir.c > > > +++ b/fs/ext4/dir.c > > > @@ -671,9 +671,11 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len, > > > const char *str, const struct qstr *name) > > > { > > > struct qstr qstr = {.name = str, .len = len }; > > > - struct inode *inode = dentry->d_parent->d_inode; > > > + const struct dentry *parent = READ_ONCE(dentry->d_parent); > > > > I'm not sure if we really need READ_ONCE d_parent here (p.s. d_parent > > won't be NULL anyway), and d_seq will guard all its validity. If I'm > > wrong, correct me kindly... > > > > Otherwise, it looks good to me... > > Reviewed-by: Gao Xiang <gaoxiang25@huawei.com> > > > > While d_parent can't be set to NULL, it can still be changed concurrently. > So we need READ_ONCE() to ensure that a consistent value is used. If I understand correctly, unlazy RCU->ref-walk will be guarded by seqlock, and for ref-walk we have d_lock (and even parent lock) in relative paths. So I prematurely think no race of renaming or unlinking evenually. I'm curious about that if experts could correct me about this. Thanks, Gao Xiang > > - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
next prev parent reply other threads:[~2020-01-24 5:27 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-01-24 4:12 [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Eric Biggers 2020-01-24 4:12 ` [f2fs-dev] " Eric Biggers 2020-01-24 5:04 ` Gao Xiang 2020-01-24 5:04 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel 2020-01-24 5:16 ` Eric Biggers 2020-01-24 5:16 ` [f2fs-dev] " Eric Biggers 2020-01-24 5:27 ` Gao Xiang [this message] 2020-01-24 5:27 ` Gao Xiang via Linux-f2fs-devel 2020-01-24 5:53 ` Eric Biggers 2020-01-24 5:53 ` [f2fs-dev] " Eric Biggers 2020-01-24 5:34 ` Gao Xiang 2020-01-24 5:34 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel 2020-01-24 5:42 ` Eric Biggers 2020-01-24 5:42 ` [f2fs-dev] " Eric Biggers 2020-01-24 6:15 ` Gao Xiang 2020-01-24 6:15 ` [f2fs-dev] " Gao Xiang via Linux-f2fs-devel 2020-01-24 18:12 ` Eric Biggers 2020-01-24 18:12 ` [f2fs-dev] " Eric Biggers 2020-01-24 18:31 ` Al Viro 2020-01-24 18:31 ` [f2fs-dev] " Al Viro 2020-01-25 3:35 ` Theodore Y. Ts'o 2020-01-25 3:35 ` [f2fs-dev] " Theodore Y. Ts'o
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20200124052740.GB31271@hsiangkao-HP-ZHAN-66-Pro-G1 \ --to=hsiangkao@aol.com \ --cc=drosen@google.com \ --cc=ebiggers@kernel.org \ --cc=krisman@collabora.com \ --cc=linux-ext4@vger.kernel.org \ --cc=linux-f2fs-devel@lists.sourceforge.net \ --cc=linux-fsdevel@vger.kernel.org \ --cc=viro@zeniv.linux.org.uk \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.