From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756142AbdC2Le1 (ORCPT ); Wed, 29 Mar 2017 07:34:27 -0400 Received: from foss.arm.com ([217.140.101.70]:60568 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756126AbdC2LeY (ORCPT ); Wed, 29 Mar 2017 07:34:24 -0400 From: Sudeep Holla Subject: Re: [PATCH 1/3] mailbox: always wait in mbox_send_message for blocking Tx mode To: Jassi Brar References: <1490095816-10943-1-git-send-email-sudeep.holla@arm.com> Cc: Sudeep Holla , Linux Kernel Mailing List , Jassi Brar , Alexey Klimov Organization: ARM Message-ID: <5f5d3202-1e67-9569-21a2-5a676bb45617@arm.com> Date: Wed, 29 Mar 2017 12:34:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/03/17 19:20, Jassi Brar wrote: > Hi Sudeep, > > On Tue, Mar 21, 2017 at 5:00 PM, Sudeep Holla wrote: >> There exists a race when msg_submit return immediately as there was an >> active request being processed which may have completed just before it's >> checked again in mbox_send_message. This will result in return to the >> caller without waiting in mbox_send_message even when it's blocking Tx. >> >> This patch fixes the issue by waiting for the completion always if Tx >> is in blocking mode. >> >> Fixes: 2b6d83e2b8b7 ("mailbox: Introduce framework for mailbox") >> Cc: Jassi Brar >> Reported-by: Alexey Klimov >> Signed-off-by: Sudeep Holla >> --- >> drivers/mailbox/mailbox.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> Hi Jassi, >> >> Here are fixes for few issues we encountered when dealing with multiple >> requests on multiple channels simultaneously. >> > Thanks for finding the bug. > > I see patch-1 tries to fix the bug. Patch-2,3 try to fix the > ramifications of the bug but they may change behaviour for some users. > Do you face any issue even after applying patch-1 ? > Unfortunately yes. Are you concerned with the change in return value on timeout ? I understand and then I chose -ETIME vs -ETIMEDOUT as hardware can still use it and we can distinguish the software timer expiry from that. Even -EIO seems incorrect for s/w timeout as it exists today, but I agree it has some impact on existing users. Also Patch 3 seems independent for me just to avoid complete call if it was empty message. Alexey also brought up another issue which is relating to ordering and may require completion flags per message instead of per channel. Today we can't guarantee that first blocker on the wait queue is same as the first in the mailbox queue. e.g.: Thread#1(T1) Thread#2(T2) mbox_send_message mbox_send_message | | V | add_to_rbuf(M1) V | add_to_rbuf(M2) | | | V V msg_submit(picks M1) msg_submit | | V V wait_for_completion(on M2) wait_for_completion(on M1) | (1st in waitQ) | (2nd in waitQ) V V wake_up(on completion of M1)<--incorrect I will let him dive in as he had some thoughts on that. -- Regards, Sudeep