From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ED599C137 for ; Thu, 25 May 2023 08:14:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92C45C433EF; Thu, 25 May 2023 08:14:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685002456; bh=fJ0ImxHlk5vtkSx7zFqdK3Q8pgeQQrfYrqrZBkpl6x0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HzV+IGBSfB2AJXqMxyOrPVN+YDwI7XBpRFUjLfKpt3I5I8iED76YS6HRXR2Pf1Piz qiBd5AD/9Ic8ehfMgDhPsqd5tt1HuZB6DPM1RU4ykZHaaH96LxquxIPP1dKE/UQ/an 3AzFDZ7rg2rAWOlGwB0GtzPVy3PdBLlf73AreD+gREDQ6t8Iy8bVyvXV4ednlDpWUn zATJSlFd0JzSDggonWR3+DWtOQmnY4DSxl47Pjy3UW49ww14oOedKKhbG4gtTczLVI eNxm0Z9Cn2qS0wo9PUeV9XAcgYq8hWnNKq+QSV7vJ/pmWR6CCe0BZQi1tuAQV8eE2e doJu8VbVukaJA== Date: Thu, 25 May 2023 10:14:06 +0200 From: Lorenzo Pieralisi To: Dexuan Cui Cc: bhelgaas@google.com, davem@davemloft.net, edumazet@google.com, haiyangz@microsoft.com, jakeo@microsoft.com, kuba@kernel.org, kw@linux.com, kys@microsoft.com, leon@kernel.org, linux-pci@vger.kernel.org, mikelley@microsoft.com, pabeni@redhat.com, robh@kernel.org, saeedm@nvidia.com, wei.liu@kernel.org, longli@microsoft.com, boqun.feng@gmail.com, ssengar@microsoft.com, helgaas@kernel.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, josete@microsoft.com, stable@vger.kernel.org Subject: Re: [PATCH v3 1/6] PCI: hv: Fix a race condition bug in hv_pci_query_relations() Message-ID: References: <20230420024037.5921-1-decui@microsoft.com> <20230420024037.5921-2-decui@microsoft.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230420024037.5921-2-decui@microsoft.com> On Wed, Apr 19, 2023 at 07:40:32PM -0700, Dexuan Cui wrote: > Fix the longstanding race between hv_pci_query_relations() and > survey_child_resources() by flushing the workqueue before we exit from > hv_pci_query_relations(). "Fix the longstanding race" is vague. Please describe the race succinctly at least to give an idea of what the problem is. > Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs") > Signed-off-by: Dexuan Cui > Reviewed-by: Michael Kelley > Cc: stable@vger.kernel.org > --- > > v2: > Removed the "debug code". > No change to the patch body. > Added Cc:stable > > v3: > Added Michael's Reviewed-by. > > drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c > index f33370b756283..b82c7cde19e66 100644 > --- a/drivers/pci/controller/pci-hyperv.c > +++ b/drivers/pci/controller/pci-hyperv.c > @@ -3308,6 +3308,19 @@ static int hv_pci_query_relations(struct hv_device *hdev) > if (!ret) > ret = wait_for_response(hdev, &comp); > > + /* > + * In the case of fast device addition/removal, it's possible that > + * vmbus_sendpacket() or wait_for_response() returns -ENODEV but we > + * already got a PCI_BUS_RELATIONS* message from the host and the > + * channel callback already scheduled a work to hbus->wq, which can be > + * running survey_child_resources() -> complete(&hbus->survey_event), > + * even after hv_pci_query_relations() exits and the stack variable > + * 'comp' is no longer valid. This can cause a strange hang issue "A strange hang" sounds like we don't understand what's happening, it does not feel like it is a solid understanding of the issue. I would remove it - given that you already explain that comp is no longer valid - that is already a bug that needs fixing. Acked-by: Lorenzo Pieralisi > + * or sometimes a page fault. Flush hbus->wq before we exit from > + * hv_pci_query_relations() to avoid the issues. > + */ > + flush_workqueue(hbus->wq); > + > return ret; > } > > -- > 2.25.1 >