From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Subject: Re: PCIe enable device races (Was: [PATCH v3] PCI: Data corruption happening due to race condition) To: Benjamin Herrenschmidt , Bjorn Helgaas Cc: Hari Vyas , bhelgaas@google.com, linux-pci@vger.kernel.org, ray.jui@broadcom.com, Jens Axboe References: <1530608741-30664-1-git-send-email-hari.vyas@broadcom.com> <20180731163727.GK45322@bhelgaas-glaptop.roam.corp.google.com> <20180815185027.GE28888@bhelgaas-glaptop.roam.corp.google.com> From: Konstantin Khlebnikov Message-ID: Date: Thu, 16 Aug 2018 10:58:43 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed List-ID: On 16.08.2018 00:52, Benjamin Herrenschmidt wrote: > On Wed, 2018-08-15 at 13:50 -0500, Bjorn Helgaas wrote: >> Yes, this is definitely broken. Some folks have tried to fix it in >> the past, but it hasn't quite happened yet. We actually merged one >> patch, 40f11adc7cd9 ("PCI: Avoid race while enabling upstream >> bridges"), but had to revert it after we found issues: >> >> https://lkml.kernel.org/r/1501858648-22228-1-git-send-email-srinath.mannam@broadcom.com >> https://lkml.kernel.org/r/20170915072352.10453.31977.stgit@bhelgaas-glaptop.roam.corp.google.com > > Ok so I had a look at this previous patch and it adds yet anothe use of > some global mutex to protect part of the operation which makes me > cringe a bit, we have too many of these. > > What do you think of the one I sent yesterday ? (I can't find it in the > archives yet) > > [RFC PATCH] pci: Proof of concept at fixing pci_enable_device/bridge races > > The patch itself needs splitting etc... but the basic idea is to move away > from those global mutexes in a number of places and have one in the pci_dev > struct itself to protect its state. > > I would also like to use this rather than the bitmap atomics for is_added > etc... (Hari's fix) in the long run. Atomics aren't significantly cheaper > and imho makes thing even messier. > > Jens, Konstantin, any chance you can test if the above also breaks iwlwifi > (I don't see why it would but ...) > I suppose original race was discovered between enabling bridge and device as described here https://lore.kernel.org/lkml/150547971091.977464.16294045866179907260.stgit@buzz/T/#u I barely can remember what I ever posted this, so I couldn't reproduce for sure. > Cheers, > Ben. > >