linux-kernel - Re: [PATCH v2] USB: host: Use zeroing memory allocator rather than allocator/memset

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Message-ID: <Pine.LNX.4.44L0.1712311617460.15484-100000@netrider.rowland.org>
Date:   Sun, 31 Dec 2017 16:20:45 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Himanshu Jha <himanshujha199640@...il.com>
cc:     gregkh@...uxfoundation.org, <mathias.nyman@...el.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <mcgrof@...nel.org>
Subject: Re: [PATCH v2] USB: host: Use zeroing memory allocator rather than
 allocator/memset

On Sun, 31 Dec 2017, Himanshu Jha wrote:

> Use dma_zalloc_coherent for allocating zeroed
> memory and remove unnecessary memset function.
> 
> Done using Coccinelle.
> Generated-by: scripts/coccinelle/api/alloc/kzalloc-simple.cocci
> 0-day tested with no failures.
> 
> Suggested-by: Luis R. Rodriguez <mcgrof@...nel.org>
> Signed-off-by: Himanshu Jha <himanshujha199640@...il.com>
> ---
> v2:
>    -align argumenst as they were before applying the SmPL rule.

For the UHCI portion:

Acked-by: Alan Stern <stern@...land.harvard.edu>

But there is something pecular about the patch...

>  drivers/usb/host/uhci-hcd.c | 7 +++----
>  drivers/usb/host/xhci-mem.c | 7 ++-----
>  2 files changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/usb/host/uhci-hcd.c b/drivers/usb/host/uhci-hcd.c
> index f5c9021..ac53398 100644
> --- a/drivers/usb/host/uhci-hcd.c
> +++ b/drivers/usb/host/uhci-hcd.c
> @@ -600,15 +600,14 @@ static int uhci_start(struct usb_hcd *hcd)
>  	uhci->dentry = dentry;
>  #endif
>  
> -	uhci->frame = dma_alloc_coherent(uhci_dev(uhci),
> -			UHCI_NUMFRAMES * sizeof(*uhci->frame),
> -			&uhci->frame_dma_handle, GFP_KERNEL);
> +	uhci->frame = dma_zalloc_coherent(uhci_dev(uhci),
> +			UHCI_NUMFRAMES * sizeof(*uhci->frame),
> +			&uhci->frame_dma_handle, GFP_KERNEL);

The second and third "changed" lines here actually are identical.  What 
program would produce a diff file showing that they were changed?

Alan Stern

>  	if (!uhci->frame) {
>  		dev_err(uhci_dev(uhci),
>  			"unable to allocate consistent memory for frame list\n");
>  		goto err_alloc_frame;
>  	}
> -	memset(uhci->frame, 0, UHCI_NUMFRAMES * sizeof(*uhci->frame));
>  
>  	uhci->frame_cpu = kcalloc(UHCI_NUMFRAMES, sizeof(*uhci->frame_cpu),
>  			GFP_KERNEL);
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 554a8a5..332420d 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -1782,14 +1782,11 @@ int xhci_alloc_erst(struct xhci_hcd *xhci,
>  	struct xhci_erst_entry *entry;
>  
>  	size = sizeof(struct xhci_erst_entry) * evt_ring->num_segs;
> -	erst->entries = dma_alloc_coherent(xhci_to_hcd(xhci)->self.sysdev,
> -					   size,
> -					   &erst->erst_dma_addr,
> -					   flags);
> +	erst->entries = dma_zalloc_coherent(xhci_to_hcd(xhci)->self.sysdev,
> +					    size, &erst->erst_dma_addr, flags);
>  	if (!erst->entries)
>  		return -ENOMEM;
>  
> -	memset(erst->entries, 0, size);
>  	erst->num_entries = evt_ring->num_segs;
>  
>  	seg = evt_ring->first_seg;
>