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SubjectRe: [PATCH 3/3] mm,page_owner: Filter out stacks by a threshold counter
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On 9/1/22 11:42 AM, Oscar Salvador wrote:> +static ssize_t read_page_owner_threshold(struct file *file, char __user *buf,
> + size_t count, loff_t *pos)
> +{
> + char *kbuf;
> + int ret = 0;
> +
> + count = min_t(size_t, count, PAGE_SIZE);
> +
> + if (*pos >= count)
> + return 0;
> +
> + kbuf = kmalloc(count, GFP_KERNEL);
> + if (!kbuf)
> + return ENOMEM;

Missing a negative sign, return -ENOMEM.

> + ret = scnprintf(kbuf, count, "%lu\n", threshold_count);
> + if (copy_to_user(buf, kbuf, ret))
> + ret = -EFAULT;
> +
> + *pos += count;
> + kfree(kbuf);
> +
> + return ret;
> +}
> +
> +static ssize_t write_page_owner_threshold(struct file *file, const char __user *buf,
> + size_t count, loff_t *pos)
> +{
> + char *kbuf;
> + int ret = 0;
> +
> + count = min_t(size_t, count, PAGE_SIZE);
> + kbuf = kmalloc(count, GFP_KERNEL);

This looks overestimating to me. For unsigned long, on a 64-bit system
has max val 18446744073709551615 (20 chars).

You can use stack a allocated local variable with length 21. No need
to use kmalloc(). The same way with the read() op.

> + if (!kbuf)
> + return -ENOMEM;
> +
> + if (copy_from_user(kbuf, buf, count)) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + kbuf[count - 1] = '\0';
> +
> + ret = kstrtoul(kbuf, 10, &threshold_count);
> +
> +out:
> + kfree(kbuf);
> + return ret ? ret : count;
> +}
> +
> +static const struct file_operations proc_page_owner_threshold = {
> + .read = read_page_owner_threshold,
> + .write = write_page_owner_threshold,
> +};

--
Ammar Faizi

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