linux-kernel - Re: [PATCH] Revert "PCI: Avoid race while enabling upstream bridges"

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Date:   Fri, 15 Sep 2017 16:28:54 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        linuxwifi@...el.com, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Srinath Mannam <srinath.mannam@...adcom.com>,
        Johannes Berg <johannes@...solutions.net>,
        Luca Coelho <luca@...lho.fi>
Subject: Re: [PATCH] Revert "PCI: Avoid race while enabling upstream bridges"

On 15.09.2017 10:23, Bjorn Helgaas wrote:
> This reverts commit 40f11adc7cd9281227f0a6a627d966dd0a5f0cd9.
> 
> Jens found that iwlwifi firmware loading failed on a Lenovo X1 Carbon,
> gen4:
> 
>    iwlwifi 0000:04:00.0: Direct firmware load for iwlwifi-8000C-34.ucode failed with error -2
>    iwlwifi 0000:04:00.0: Direct firmware load for iwlwifi-8000C-33.ucode failed with error -2
>    iwlwifi 0000:04:00.0: Direct firmware load for iwlwifi-8000C-32.ucode failed with error -2
>    iwlwifi 0000:04:00.0: loaded firmware version 31.532993.0 op_mode iwlmvm
>    iwlwifi 0000:04:00.0: Detected Intel(R) Dual Band Wireless AC 8260, REV=0x208
>    ...
>    iwlwifi 0000:04:00.0: Failed to load firmware chunk!
>    iwlwifi 0000:04:00.0: Could not load the [0] uCode section
>    iwlwifi 0000:04:00.0: Failed to start INIT ucode: -110
>    iwlwifi 0000:04:00.0: Failed to run INIT ucode: -110
> 
> He bisected it to 40f11adc7cd9 ("PCI: Avoid race while enabling upstream
> bridges").  Revert that commit to fix the regression.

I've found this too. Bug in fast-path: reverting last hunk is enough
http://lkml.kernel.org/r/150547971091.977464.16294045866179907260.stgit@buzz

> 
> Link: http://lkml.kernel.org/r/4bcbcbc1-7c79-09f0-5071-bc2f53bf6574@kernel.dk
> Fixes: 40f11adc7cd9 ("PCI: Avoid race while enabling upstream bridges")
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> CC: Srinath Mannam <srinath.mannam@...adcom.com>
> CC: Jens Axboe <axboe@...nel.dk>
> CC: Luca Coelho <luca@...lho.fi>
> CC: Johannes Berg <johannes@...solutions.net>
> CC: Emmanuel Grumbach <emmanuel.grumbach@...el.com>
> ---
>   drivers/pci/pci.c |   13 ++-----------
>   1 file changed, 2 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b0002daa50f3..6078dfc11b11 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -52,7 +52,6 @@ static void pci_pme_list_scan(struct work_struct *work);
>   static LIST_HEAD(pci_pme_list);
>   static DEFINE_MUTEX(pci_pme_list_mutex);
>   static DECLARE_DELAYED_WORK(pci_pme_work, pci_pme_list_scan);
> -static DEFINE_MUTEX(pci_bridge_mutex);
>   
>   struct pci_pme_device {
>   	struct list_head list;
> @@ -1351,16 +1350,10 @@ static void pci_enable_bridge(struct pci_dev *dev)
>   	if (bridge)
>   		pci_enable_bridge(bridge);
>   
> -	/*
> -	 * Hold pci_bridge_mutex to prevent a race when enabling two
> -	 * devices below the bridge simultaneously.  The race may cause a
> -	 * PCI_COMMAND_MEMORY update to be lost (see changelog).
> -	 */
> -	mutex_lock(&pci_bridge_mutex);
>   	if (pci_is_enabled(dev)) {
>   		if (!dev->is_busmaster)
>   			pci_set_master(dev);
> -		goto end;
> +		return;
>   	}
>   
>   	retval = pci_enable_device(dev);
> @@ -1368,8 +1361,6 @@ static void pci_enable_bridge(struct pci_dev *dev)
>   		dev_err(&dev->dev, "Error enabling bridge (%d), continuing\n",
>   			retval);
>   	pci_set_master(dev);
> -end:
> -	mutex_unlock(&pci_bridge_mutex);
>   }
>   
>   static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags)
> @@ -1394,7 +1385,7 @@ static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags)
>   		return 0;		/* already enabled */
>   
>   	bridge = pci_upstream_bridge(dev);
> -	if (bridge && !pci_is_enabled(bridge))
> +	if (bridge)
>   		pci_enable_bridge(bridge);
>   
>   	/* only skip sriov related */
> 
>