Re: [PATCH v2 1/3] virtio-rng cleanup: move some code out of mutex protection

Michael Büsch
2014-09-15T16:37:00Z

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On Tue, 16 Sep 2014 00:02:27 +0800
Amos Kong <akong@redhat.com> wrote:

> It doesn't save too much cpu time as expected, just a cleanup.
>
> Signed-off-by: Amos Kong <akong@redhat.com>
> ---
> drivers/char/hw_random/core.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index aa30a25..c591d7e 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -270,8 +270,8 @@ static ssize_t hwrng_attr_current_show(struct device *dev,
> return -ERESTARTSYS;
> if (current_rng)
> name = current_rng->name;
> - ret = snprintf(buf, PAGE_SIZE, "%s\n", name);
> mutex_unlock(&rng_mutex);
> + ret = snprintf(buf, PAGE_SIZE, "%s\n", name);

I'm not sure this is safe.
Name is just a pointer.
What if the hwrng gets unregistered after unlock and just before the snprintf?

> return ret;
> }
> @@ -284,19 +284,19 @@ static ssize_t hwrng_attr_available_show(struct device *dev,
> ssize_t ret = 0;
> struct hwrng *rng;
>
> + buf[0] = '\0';
> err = mutex_lock_interruptible(&rng_mutex);
> if (err)
> return -ERESTARTSYS;
> - buf[0] = '\0';
> list_for_each_entry(rng, &rng_list, list) {
> strncat(buf, rng->name, PAGE_SIZE - ret - 1);
> ret += strlen(rng->name);
> strncat(buf, " ", PAGE_SIZE - ret - 1);
> ret++;
> }
> + mutex_unlock(&rng_mutex);
> strncat(buf, "\n", PAGE_SIZE - ret - 1);
> ret++;
> - mutex_unlock(&rng_mutex);
>
> return ret;
> }

This looks ok.

--
Michael

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