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Date: Thu, 23 Jan 2020 21:16:01 -0800 From: Eric Biggers <ebiggers@...nel.org> To: Gao Xiang <hsiangkao@....com> Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, Alexander Viro <viro@...iv.linux.org.uk>, Daniel Rosenberg <drosen@...gle.com>, Gabriel Krisman Bertazi <krisman@...labora.com> Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() 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@...wei.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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