Return-Path: Received: from mail-io0-f196.google.com ([209.85.223.196]:36243 "EHLO mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752260AbcCaQij (ORCPT ); Thu, 31 Mar 2016 12:38:39 -0400 Received: by mail-io0-f196.google.com with SMTP id e3so14270901ioa.3 for ; Thu, 31 Mar 2016 09:38:38 -0700 (PDT) Received: from manet.1015granger.net ([2604:8800:100:81fc:ec4:7aff:fe6c:1dce]) by smtp.gmail.com with ESMTPSA id 99sm4108454ior.16.2016.03.31.09.38.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Mar 2016 09:38:37 -0700 (PDT) Subject: [PATCH RFCv3] NFS: Fix an LOCK/OPEN race when unlinking an open file From: Chuck Lever To: linux-nfs@vger.kernel.org Date: Thu, 31 Mar 2016 12:38:35 -0400 Message-ID: <20160331163835.2791.6712.stgit@manet.1015granger.net> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: At Connectathon 2016, we found that recent upstream Linux clients would occasionally send a LOCK operation with a zero stateid. This appeared to happen in close proximity to another thread returning a delegation before unlinking the same file while it remained open. Earlier, the client received a write delegation on this file and returned the open stateid. Now, as it is getting ready to unlink the file, it returns the write delegation. But there is still an open file descriptor on that file, so the client must OPEN the file again before it returns the delegation. Since commit 24311f884189 ('NFSv4: Recovery of recalled read delegations is broken'), nfs_open_delegation_recall() clears the NFS_DELEGATED_STATE flag _before_ it sends the OPEN. This allows a racing LOCK on the same inode to be put on the wire before the OPEN operation has returned a valid open stateid. To eliminate this race, serialize delegation return with the acquisition of a file lock on the same file. Adopt the same approach as is used in the unlock path. Fixes: 24311f884189 ('NFSv4: Recovery of recalled read ... ') Signed-off-by: Chuck Lever --- fs/nfs/nfs4proc.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c index 01bef06..c40f1b6 100644 --- a/fs/nfs/nfs4proc.c +++ b/fs/nfs/nfs4proc.c @@ -6054,6 +6054,7 @@ static int nfs41_lock_expired(struct nfs4_state *state, struct file_lock *reques static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock *request) { struct nfs_inode *nfsi = NFS_I(state->inode); + struct nfs4_state_owner *sp = state->owner; unsigned char fl_flags = request->fl_flags; int status = -ENOLCK; @@ -6068,6 +6069,7 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock status = do_vfs_lock(state->inode, request); if (status < 0) goto out; + mutex_lock(&sp->so_delegreturn_mutex); down_read(&nfsi->rwsem); if (test_bit(NFS_DELEGATED_STATE, &state->flags)) { /* Yes: cache locks! */ @@ -6075,9 +6077,11 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock request->fl_flags = fl_flags & ~FL_SLEEP; status = do_vfs_lock(state->inode, request); up_read(&nfsi->rwsem); + mutex_unlock(&sp->so_delegreturn_mutex); goto out; } up_read(&nfsi->rwsem); + mutex_unlock(&sp->so_delegreturn_mutex); status = _nfs4_do_setlk(state, cmd, request, NFS_LOCK_NEW); out: request->fl_flags = fl_flags;