linux-kernel - [PATCH] usb: dwc2: use struct

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Message-ID: <20190218185937.GA16947@embeddedor>
Date:   Mon, 18 Feb 2019 12:59:37 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Minas Harutyunyan <hminas@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] usb: dwc2: use struct_size() in kzalloc()

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
    int stuff;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = kzalloc(size, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL);

Notice that, in this case, variable size is not necessary, hence
it is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/usb/dwc2/hcd.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index dd82fa516f3f..3f087962f498 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -3981,10 +3981,8 @@ static struct dwc2_hcd_urb *dwc2_hcd_urb_alloc(struct dwc2_hsotg *hsotg,
 					       gfp_t mem_flags)
 {
 	struct dwc2_hcd_urb *urb;
-	u32 size = sizeof(*urb) + iso_desc_count *
-		   sizeof(struct dwc2_hcd_iso_packet_desc);
 
-	urb = kzalloc(size, mem_flags);
+	urb = kzalloc(struct_size(urb, iso_descs, iso_desc_count), mem_flags);
 	if (urb)
 		urb->packet_count = iso_desc_count;
 	return urb;
-- 
2.20.1