linux-kernel - RE: [PATCH 2/2] pci: host: pci-hyperv: Replace GFP_ATOMIC with GFP_KERNEL in new_pcichild

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Message-ID: <DM5PR2101MB10305A8292BCC1F75AC578C3DCD50@DM5PR2101MB1030.namprd21.prod.outlook.com>
Date:   Sun, 18 Mar 2018 22:42:00 +0000
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>
CC:     "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] pci: host: pci-hyperv: Replace GFP_ATOMIC with
 GFP_KERNEL in new_pcichild_device

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> On Behalf
> Of Jia-Ju Bai
> Sent: Sunday, March 18, 2018 7:53 AM
> To: KY Srinivasan <kys@...rosoft.com>; Haiyang Zhang <haiyangz@...rosoft.com>; Stephen
> Hemminger <sthemmin@...rosoft.com>; bhelgaas@...gle.com
> Cc: devel@...uxdriverproject.org; linux-pci@...r.kernel.org; linux-kernel@...r.kernel.org;
> Jia-Ju Bai <baijiaju1990@...il.com>
> Subject: [PATCH 2/2] pci: host: pci-hyperv: Replace GFP_ATOMIC with GFP_KERNEL in
> new_pcichild_device
> 
> new_pcichild_device() is not called in atomic context.
> 
> The call chain ending up at new_pcichild_device() is:
> [1] new_pcichild_device() <- pci_devices_present_work()
> pci_devices_present_work() is only set in INIT_WORK().
> 
> Despite never getting called from atomic context,
> new_pcichild_device() calls kzalloc with GFP_ATOMIC,
> which waits busily for allocation.
> GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL
> to avoid busy waiting.
> 
> This is found by a static analysis tool named DCNS written by myself.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>

> ---
>  drivers/pci/host/pci-hyperv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
> index 0fe3ea1..289e31d 100644
> --- a/drivers/pci/host/pci-hyperv.c
> +++ b/drivers/pci/host/pci-hyperv.c
> @@ -1500,7 +1500,7 @@ static struct hv_pci_dev *new_pcichild_device(struct
> hv_pcibus_device *hbus,
>  	unsigned long flags;
>  	int ret;
> 
> -	hpdev = kzalloc(sizeof(*hpdev), GFP_ATOMIC);
> +	hpdev = kzalloc(sizeof(*hpdev), GFP_KERNEL);
>  	if (!hpdev)
>  		return NULL;
> 
> --
> 1.9.1