From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomas Bortoli Subject: Re: [PATCH] net/p9/trans_fd.c: fix double list_del() Date: Mon, 23 Jul 2018 18:51:34 +0200 Message-ID: <8c11b552-b5d7-120c-0ac1-2c62162c10af@gmail.com> References: <20180723121902.20201-1-tomasbortoli@gmail.com> <20180723125701.GA17971@nautica> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: ericvh@gmail.com, rminnich@sandia.gov, lucho@ionkov.net, jiangyiwen@huawei.com, davem@davemloft.net, v9fs-developer@lists.sourceforge.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller@googlegroups.com To: Dominique Martinet Return-path: In-Reply-To: <20180723125701.GA17971@nautica> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 07/23/2018 02:57 PM, Dominique Martinet wrote: > Tomas Bortoli wrote on Mon, Jul 23, 2018: >> A double list_del(&req->req_list) is possible in p9_fd_cancel() as >> shown by Syzbot. To prevent it we have to ensure that we have the >> client->lock when deleting the list. Furthermore, we have to update >> the status of the request before releasing the lock, to prevent the >> race. > > Nice, so no need to change the list_del to list_del_init! > > I still have a nitpick on the last moved unlock, but it's mostly > aesthetic - the change looks much better to me now. > > (Since that will require a v2 I'll be evil and go further than Yiwen > about the commit message: let it breathe a bit! :) I think a line break > before "furthermore" for example will make it easier to read) > agree >> >> Signed-off-by: Tomas Bortoli >> Reported-by: syzbot+735d926e9d1317c3310c@syzkaller.appspotmail.com >> --- >> net/9p/trans_fd.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c >> index a64b01c56e30..370c6c69a05c 100644 >> --- a/net/9p/trans_fd.c >> +++ b/net/9p/trans_fd.c >> @@ -199,15 +199,14 @@ static void p9_mux_poll_stop(struct p9_conn *m) >> static void p9_conn_cancel(struct p9_conn *m, int err) >> { >> struct p9_req_t *req, *rtmp; >> - unsigned long flags; >> LIST_HEAD(cancel_list); >> >> p9_debug(P9_DEBUG_ERROR, "mux %p err %d\n", m, err); >> >> - spin_lock_irqsave(&m->client->lock, flags); >> + spin_lock(&m->client->lock); >> >> if (m->err) { >> - spin_unlock_irqrestore(&m->client->lock, flags); >> + spin_unlock(&m->client->lock); >> return; >> } >> >> @@ -219,7 +218,6 @@ static void p9_conn_cancel(struct p9_conn *m, int err) >> list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) { >> list_move(&req->req_list, &cancel_list); >> } >> - spin_unlock_irqrestore(&m->client->lock, flags); >> >> list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) { >> p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req); >> @@ -228,6 +226,7 @@ static void p9_conn_cancel(struct p9_conn *m, int err) >> req->t_err = err; >> p9_client_cb(m->client, req, REQ_STATUS_ERROR); >> } >> + spin_unlock(&m->client->lock); >> } >> >> static __poll_t >> @@ -370,12 +369,12 @@ static void p9_read_work(struct work_struct *work) >> if (m->req->status != REQ_STATUS_ERROR) >> status = REQ_STATUS_RCVD; >> list_del(&m->req->req_list); >> - spin_unlock(&m->client->lock); >> p9_client_cb(m->client, m->req, status); >> m->rc.sdata = NULL; >> m->rc.offset = 0; >> m->rc.capacity = 0; >> m->req = NULL; >> + spin_unlock(&m->client->lock); > > It took me a while to understand why you extended this lock despite > having just read the commit message, I'd suggest: > - moving the spin_unlock to right after p9_client_cb (afterall that's > what we want, the m->rc and m->req don't need to be protected) yes, better. > - add a comment before p9_client_cb saying something like 'updates > req->status' or try to explain why it needs to be locked here but other > transports don't need such a lock (they're not dependant on req->status > like this) > ok thanks for the feedback