From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5776AC433FF for ; Thu, 1 Aug 2019 08:22:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A126216C8 for ; Thu, 1 Aug 2019 08:22:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564647768; bh=s5dXhkpeJafPwDVl5s4Gi0HS4FzDwC6D0rY9X0wyKfk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=eS0fkRWaLnamBPwWn6d24wB7rwGfpOkk+AsFLY3SvA3LnPqAVvztwotkLybOqLXg+ 1zV5sgX2xML5bFAxa+5HuDMNc/+12PTTuoflt1Qkgnr3xjB4xKEjjAekl+oa/PftMZ yXb8HO/6pKrc6XaTOW5u6reOTOpMazDLGSzRHM1A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726514AbfHAIWr (ORCPT ); Thu, 1 Aug 2019 04:22:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:40158 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726381AbfHAIWr (ORCPT ); Thu, 1 Aug 2019 04:22:47 -0400 Received: from localhost (unknown [193.47.165.251]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 253682087E; Thu, 1 Aug 2019 08:22:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564647766; bh=s5dXhkpeJafPwDVl5s4Gi0HS4FzDwC6D0rY9X0wyKfk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BlByyLIyeYvQXIGUdRoZ1MfXALsdAWfWel272Gr/3Ob8Fe2a/0pLfrmXiHV5aYavx N9NwkNb4AIaZjjnRMSt/EnCMiM8uF2Ulf7kvFNg7R0IyF3JkencXFcftSgYjWWz9uT DuvqBZJgIo0EFcMfAQf3Wx35IeheEfWRPf5kOcBE= Date: Thu, 1 Aug 2019 11:22:43 +0300 From: Leon Romanovsky To: Doug Ledford Cc: Jason Gunthorpe , RDMA mailing list , Saeed Mahameed Subject: Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister Message-ID: <20190801082243.GG4832@mtr-leonro.mtl.com> References: <20190731083852.584-1-leon@kernel.org> <44863abbef5c1e233cbedfdf959fe900f7722d74.camel@redhat.com> <20190731170054.GF22677@mellanox.com> <20190731170944.GC4832@mtr-leonro.mtl.com> <20190731172215.GJ22677@mellanox.com> <20190731180124.GE4832@mtr-leonro.mtl.com> <805ad5c2714ad2fb4c9b92eb99a256e8998334f9.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <805ad5c2714ad2fb4c9b92eb99a256e8998334f9.camel@redhat.com> User-Agent: Mutt/1.12.0 (2019-05-25) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Wed, Jul 31, 2019 at 02:51:42PM -0400, Doug Ledford wrote: > On Wed, 2019-07-31 at 21:01 +0300, Leon Romanovsky wrote: > > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote: > > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote: > > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote: > > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote: > > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c > > > > > > > b/drivers/infiniband/hw/mlx5/main.c > > > > > > > index c2a5780cb394..e12a4404096b 100644 > > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c > > > > > > > @@ -5802,13 +5802,12 @@ static void > > > > > > > mlx5_ib_unbind_slave_port(struct > > > > > > > mlx5_ib_dev *ibdev, > > > > > > > return; > > > > > > > } > > > > > > > > > > > > > > - if (mpi->mdev_events.notifier_call) > > > > > > > - mlx5_notifier_unregister(mpi->mdev, &mpi- > > > > > > > >mdev_events); > > > > > > > - mpi->mdev_events.notifier_call = NULL; > > > > > > > - > > > > > > > mpi->ibdev = NULL; > > > > > > > > > > > > > > spin_unlock(&port->mp.mpi_lock); > > > > > > > + if (mpi->mdev_events.notifier_call) > > > > > > > + mlx5_notifier_unregister(mpi->mdev, &mpi- > > > > > > > >mdev_events); > > > > > > > + mpi->mdev_events.notifier_call = NULL; > > > > > > > > > > > > I can see where this fixes the problem at hand, but this gives > > > > > > the > > > > > > appearance of creating a new race. Doing a > > > > > > check/unregister/set-null > > > > > > series outside of any locks is a red flag to someone > > > > > > investigating the > > > > > > code. You should at least make note of the fact that calling > > > > > > unregister > > > > > > more than once is safe. If you're fine with it, I can add a > > > > > > comment and > > > > > > take the patch, or you can resubmit. > > > > > > > > > > Mucking about notifier_call like that is gross anyhow, maybe > > > > > better to > > > > > delete it entirely. > > > > > > > > What do you propose to delete? > > > > > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if > > > (mpi->mdev_events.notifier_call)' > > > > > > Once it leaves the lock it stops doing anything useful. > > > > > > If you need it, then we can't drop the lock, if you don't, it is > > > just > > > dead code, delete it. > > > > This specific notifier_call is protected outside > > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL > > check > > is needed to ensure single call to mlx5_notifier_unregister, because > > calls to mlx5_ib_unbind_slave_port() will be serialized. > > But looking at the code, it doesn't appear mlx5_notifier_unregister > requires there to only be a single call. It's safe to call it multiple > times for the same notifier. I think so. > > -- > Doug Ledford > GPG KeyID: B826A3330E572FDD > Fingerprint = AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 2FDD