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From: Eric Biggers <ebiggers@kernel.org>
To: Gao Xiang <hsiangkao@aol.com>
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: Thu, 23 Jan 2020 21:16:01 -0800	[thread overview]
Message-ID: <20200124051601.GB832@sol.localdomain> (raw)
In-Reply-To: <20200124050423.GA31271@hsiangkao-HP-ZHAN-66-Pro-G1>

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.

- Eric

WARNING: multiple messages have this Message-ID (diff)
From: Eric Biggers <ebiggers@kernel.org>
To: Gao Xiang <hsiangkao@aol.com>
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: Thu, 23 Jan 2020 21:16:01 -0800	[thread overview]
Message-ID: <20200124051601.GB832@sol.localdomain> (raw)
In-Reply-To: <20200124050423.GA31271@hsiangkao-HP-ZHAN-66-Pro-G1>

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.

- Eric


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  reply	other threads:[~2020-01-24  5:16 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 [this message]
2020-01-24  5:16     ` Eric Biggers
2020-01-24  5:27     ` Gao Xiang
2020-01-24  5:27       ` [f2fs-dev] " 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

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