From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754383AbdJIRPW (ORCPT ); Mon, 9 Oct 2017 13:15:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:50544 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754161AbdJIRPU (ORCPT ); Mon, 9 Oct 2017 13:15:20 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91C05218BB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=helgaas@kernel.org Date: Mon, 9 Oct 2017 12:15:17 -0500 From: Bjorn Helgaas To: Jia-Ju Bai Cc: patrik.r.jakobsson@gmail.com, airlied@linux.ie, bhelgaas@google.com, forest@alittletooquiet.net, gregkh@linuxfoundation.org, simon@nikanor.nu, scott@matheina.com, tvboxspy@gmail.com, dan.a.cashman@gmail.com, golubev.mikhail@gmail.com, devel@driverdev.osuosl.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Rafael J. Wysocki" , linux-pm@vger.kernel.org Subject: Re: [PATCH] pci: Fix a possible sleep-in-atomic bug in pci_set_power_state Message-ID: <20171009171517.GL25517@bhelgaas-glaptop.roam.corp.google.com> References: <1507536980-9345-1-git-send-email-baijiaju1990@163.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1507536980-9345-1-git-send-email-baijiaju1990@163.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [+cc Rafael, linux-pm] Hi Jia-Ju, On Mon, Oct 09, 2017 at 04:16:20PM +0800, Jia-Ju Bai wrote: > The drivers vt6655 and gma500 call pci_set_power_state under a spinlock, which may sleep. > The function call paths are: > gma_power_begin (acquire the spinlock) (drivers/gpu/drm/gma500/power.c) > gma_resume_pci > pci_set_power_state > __pci_start_power_transition (drivers/pci/pci.c) > msleep --> may sleep > > gma_power_begin (acquire the spinlock) (drivers/gpu/drm/gma500/power.c) > gma_resume_pci > pci_enable_device > pci_enable_device_flags (drivers/pci/pci.c) > do_pci_enable_device > pci_set_power_state > __pci_start_power_transition > msleep --> may sleep > > vt6655_suspend (acquire the spinlock) (drivers/staging/vt6655/device_main.c) > pci_set_power_state > __pci_start_power_transition (drivers/pci/pci.c) > msleep --> may sleep > > To fix these bugs, msleep is replaced with mdelay in __pci_start_power_transition > > These bugs are found by my static analysis tool and my code review. We can either - change pci_set_power_state() so it can be called while holding a spinlock (as this patch does), or - change the drivers so they don't hold the spinlock while calling pci_set_power_state(). I think the latter is better because d3cold_delay is typically 100ms, and that's a long time to spin with interrupts disabled. I assume it's easy to produce an actual failure here? Why haven't we seen bug reports about this? Bjorn > Signed-off-by: Jia-Ju Bai > --- > drivers/pci/pci.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 6078dfc..7b763a3 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -823,7 +823,7 @@ static void __pci_start_power_transition(struct pci_dev *dev, pci_power_t state) > */ > if (dev->runtime_d3cold) { > if (dev->d3cold_delay) > - msleep(dev->d3cold_delay); > + mdelay(dev->d3cold_delay); > /* > * When powering on a bridge from D3cold, the > * whole hierarchy may be powered on into > -- > 1.7.9.5 > >