linux-kernel - [PATCH] irqchip/qcom: Use struct_size() in devm

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Date:   Tue, 4 Jun 2019 18:16:16 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Andy Gross <agross@...nel.org>,
        David Brown <david.brown@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] irqchip/qcom: Use struct_size() in devm_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 = devm_kzalloc(dev, size, GFP_KERNEL);

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

instance = devm_kzalloc(dev, struct_size(instance, entry, count), GFP_KERNEL);

Notice that, in this case, variable alloc_sz 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/irqchip/qcom-irq-combiner.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/qcom-irq-combiner.c b/drivers/irqchip/qcom-irq-combiner.c
index 7f0c0be322e0..d269a7722032 100644
--- a/drivers/irqchip/qcom-irq-combiner.c
+++ b/drivers/irqchip/qcom-irq-combiner.c
@@ -237,7 +237,6 @@ static int get_registers(struct platform_device *pdev, struct combiner *comb)
 static int __init combiner_probe(struct platform_device *pdev)
 {
 	struct combiner *combiner;
-	size_t alloc_sz;
 	int nregs;
 	int err;
 
@@ -247,8 +246,8 @@ static int __init combiner_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	alloc_sz = sizeof(*combiner) + sizeof(struct combiner_reg) * nregs;
-	combiner = devm_kzalloc(&pdev->dev, alloc_sz, GFP_KERNEL);
+	combiner = devm_kzalloc(&pdev->dev, struct_size(combiner, regs, nregs),
+				GFP_KERNEL);
 	if (!combiner)
 		return -ENOMEM;
 
-- 
2.21.0