From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Al Viro" , "Dae R. Jeong" Date: Sun, 11 Nov 2018 19:49:05 +0000 Message-ID: Subject: [PATCH 3.16 320/366] make sure that __dentry_kill() always invalidates d_seq, unhashed or not In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.16.61-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit 4c0d7cd5c8416b1ef41534d19163cb07ffaa03ab upstream. RCU pathwalk relies upon the assumption that anything that changes ->d_inode of a dentry will invalidate its ->d_seq. That's almost true - the one exception is that the final dput() of already unhashed dentry does *not* touch ->d_seq at all. Unhashing does, though, so for anything we'd found by RCU dcache lookup we are fine. Unfortunately, we can *start* with an unhashed dentry or jump into it. We could try and be careful in the (few) places where that could happen. Or we could just make the final dput() invalidate the damn thing, unhashed or not. The latter is much simpler and easier to backport, so let's do it that way. Reported-by: "Dae R. Jeong" Signed-off-by: Al Viro Signed-off-by: Ben Hutchings --- fs/dcache.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -340,14 +340,11 @@ static void dentry_unlink_inode(struct d __releases(dentry->d_inode->i_lock) { struct inode *inode = dentry->d_inode; - bool hashed = !d_unhashed(dentry); - if (hashed) - raw_write_seqcount_begin(&dentry->d_seq); + raw_write_seqcount_begin(&dentry->d_seq); __d_clear_type_and_inode(dentry); hlist_del_init(&dentry->d_u.d_alias); - if (hashed) - raw_write_seqcount_end(&dentry->d_seq); + raw_write_seqcount_end(&dentry->d_seq); spin_unlock(&dentry->d_lock); spin_unlock(&inode->i_lock); if (!inode->i_nlink)