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
next prev parent reply other threads:[~2020-01-24 5:27 UTC|newest]
Thread overview: 11+ 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 5:04 ` Gao Xiang
2020-01-24 5:16 ` Eric Biggers
2020-01-24 5:27 ` Gao Xiang [this message]
2020-01-24 5:53 ` Eric Biggers
2020-01-24 5:34 ` Gao Xiang
2020-01-24 5:42 ` Eric Biggers
2020-01-24 6:15 ` Gao Xiang
2020-01-24 18:12 ` Eric Biggers
2020-01-24 18:31 ` Al Viro
2020-01-25 3:35 ` Theodore Y. Ts'o
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