From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman Subject: [PATCH 3.14 029/130] dealing with the rest of shrink_dentry_list() livelock To: Cc: Greg Kroah-Hartman , , Al Viro Message-Id: <20160301234500.791010389@linuxfoundation.org> In-Reply-To: <20160301234459.768886030@linuxfoundation.org> References: <20160301234459.768886030@linuxfoundation.org> Date: Tue, 01 Mar 2016 23:50:59 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit b2b80195d8829921506880f6dccd21cabd163d0d upstream. We have the same problem with ->d_lock order in the inner loop, where we are dropping references to ancestors. Same solution, basically - instead of using dentry_kill() we use lock_parent() (introduced in the previous commit) to get that lock in a safe way, recheck ->d_count (in case if lock_parent() has ended up dropping and retaking ->d_lock and somebody managed to grab a reference during that window), trylock the inode->i_lock and use __dentry_kill() to do the rest. Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/dcache.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -886,8 +886,26 @@ static void shrink_dentry_list(struct li * fragmentation. */ dentry = parent; - while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) - dentry = dentry_kill(dentry, 1); + while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) { + parent = lock_parent(dentry); + if (dentry->d_lockref.count != 1) { + dentry->d_lockref.count--; + spin_unlock(&dentry->d_lock); + if (parent) + spin_unlock(&parent->d_lock); + break; + } + inode = dentry->d_inode; /* can't be NULL */ + if (unlikely(!spin_trylock(&inode->i_lock))) { + spin_unlock(&dentry->d_lock); + if (parent) + spin_unlock(&parent->d_lock); + cpu_relax(); + continue; + } + __dentry_kill(dentry); + dentry = parent; + } } }