linux-kernel - Re: [PATCH v4 3/4] PCI: hv: Remove hbus->enum

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Message-ID: <20180316105424.GA24198@e107981-ln.cambridge.arm.com>
Date:   Fri, 16 Mar 2018 10:54:24 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
Subject: Re: [PATCH v4 3/4] PCI: hv: Remove hbus->enum_sem

On Thu, Mar 15, 2018 at 02:21:51PM +0000, Dexuan Cui wrote:
> Since we serialize the present/eject work items now, we don't need the
> semaphore any more.
> 
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> Acked-by: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> Cc: Jack Morgenstein <jackm@...lanox.com>
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: K. Y. Srinivasan <kys@...rosoft.com>
> ---
>  drivers/pci/host/pci-hyperv.c | 17 ++---------------
>  1 file changed, 2 insertions(+), 15 deletions(-)

Dexuan,

while applying/updating these patches I notice this one may be squashed
into:

https://patchwork.ozlabs.org/patch/886266/

since they logically belong in the same patch. Are you OK with me doing
that ? Is my reading correct ?

Thanks,
Lorenzo

> diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
> index 1d2e1cb617f4..0dc2ecdbbe45 100644
> --- a/drivers/pci/host/pci-hyperv.c
> +++ b/drivers/pci/host/pci-hyperv.c
> @@ -447,7 +447,6 @@ struct hv_pcibus_device {
>  	spinlock_t device_list_lock;	/* Protect lists below */
>  	void __iomem *cfg_addr;
>  
> -	struct semaphore enum_sem;
>  	struct list_head resources_for_children;
>  
>  	struct list_head children;
> @@ -1648,12 +1647,8 @@ static struct hv_pci_dev *get_pcichild_wslot(struct hv_pcibus_device *hbus,
>   * It must also treat the omission of a previously observed device as
>   * notification that the device no longer exists.
>   *
> - * Note that this function is a work item, and it may not be
> - * invoked in the order that it was queued.  Back to back
> - * updates of the list of present devices may involve queuing
> - * multiple work items, and this one may run before ones that
> - * were sent later. As such, this function only does something
> - * if is the last one in the queue.
> + * Note that this function is serialized with hv_eject_device_work(),
> + * because both are pushed to the ordered workqueue hbus->wq.
>   */
>  static void pci_devices_present_work(struct work_struct *work)
>  {
> @@ -1674,11 +1669,6 @@ static void pci_devices_present_work(struct work_struct *work)
>  
>  	INIT_LIST_HEAD(&removed);
>  
> -	if (down_interruptible(&hbus->enum_sem)) {
> -		put_hvpcibus(hbus);
> -		return;
> -	}
> -
>  	/* Pull this off the queue and process it if it was the last one. */
>  	spin_lock_irqsave(&hbus->device_list_lock, flags);
>  	while (!list_empty(&hbus->dr_list)) {
> @@ -1695,7 +1685,6 @@ static void pci_devices_present_work(struct work_struct *work)
>  	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
>  
>  	if (!dr) {
> -		up(&hbus->enum_sem);
>  		put_hvpcibus(hbus);
>  		return;
>  	}
> @@ -1782,7 +1771,6 @@ static void pci_devices_present_work(struct work_struct *work)
>  		break;
>  	}
>  
> -	up(&hbus->enum_sem);
>  	put_hvpcibus(hbus);
>  	kfree(dr);
>  }
> @@ -2516,7 +2504,6 @@ static int hv_pci_probe(struct hv_device *hdev,
>  	spin_lock_init(&hbus->config_lock);
>  	spin_lock_init(&hbus->device_list_lock);
>  	spin_lock_init(&hbus->retarget_msi_interrupt_lock);
> -	sema_init(&hbus->enum_sem, 1);
>  	init_completion(&hbus->remove_event);
>  	hbus->wq = alloc_ordered_workqueue("hv_pci_%x", 0,
>  					   hbus->sysdata.domain);
> -- 
> 2.7.4
>