On Wed, Aug 31, 2022 at 05:20:24PM +0000, Sven van Ashbrook wrote:
> The hwrng fill function runs as a normal kthread. This thread
> doesn't get frozen by the PM, i.e. it will keep running during,
> or in, system suspend. It may call the client driver's
> data_present()/data_read() functions during, or in, suspend;
> which may generate errors or warnings. For example, if the
> client driver uses an i2c bus, the following warning may be
> intermittently generated:
>
> i2c: Transfer while suspended
>
> Fix by converting the delay polled kthread into an ordered work
> queue running a single, self-rearming delayed_work. Make the
> workqueue WQ_FREEZABLE, so the PM will drain any work items
> before going into suspend. This prevents client drivers from
> being accessed during, or in, suspend.
>
> Tested on a Chromebook containing an cr50 tpm over i2c. The test
> consists of 31000 suspend/resume cycles. Occasional
> "i2c: Transfer while suspended" warnings are seen. After applying
> this patch, these warnings disappear.
>
> This patch also does not appear to cause any regressions on the
> ChromeOS test queues.
>
> Signed-off-by: Sven van Ashbrook <svenva@xxxxxxxxxxxx>
The general concept seems to be fine.
> - if (rc <= 0) {
> - pr_warn("hwrng: no data available\n");
> - msleep_interruptible(10000);
> - continue;
> - }
> + if (!quality)
> + return;
>
> + if (rc > 0) {
> /* If we cannot credit at least one bit of entropy,
> * keep track of the remainder for the next iteration
> */
You need to refresh your patch-set against the latest tree. This
function has changed quite a bit.
> @@ -541,14 +536,12 @@ static void hwrng_manage_rngd(struct hwrng *rng)
> if (WARN_ON(!mutex_is_locked(&rng_mutex)))
> return;
>
> - if (rng->quality == 0 && hwrng_fill)
> - kthread_stop(hwrng_fill);
> - if (rng->quality > 0 && !hwrng_fill) {
> - hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
> - if (IS_ERR(hwrng_fill)) {
> - pr_err("hwrng_fill thread creation failed\n");
> - hwrng_fill = NULL;
> - }
> + if (rng->quality == 0 && is_hwrng_wq_running) {
> + cancel_delayed_work(&hwrng_fill_dwork);
> + is_hwrng_wq_running = false;
> + } else if (rng->quality > 0 && !is_hwrng_wq_running) {
> + mod_delayed_work(hwrng_wq, &hwrng_fill_dwork, 0);
> + is_hwrng_wq_running = true;
> }
> }
>
> @@ -631,8 +624,7 @@ void hwrng_unregister(struct hwrng *rng)
> new_rng = get_current_rng_nolock();
> if (list_empty(&rng_list)) {
> mutex_unlock(&rng_mutex);
> - if (hwrng_fill)
> - kthread_stop(hwrng_fill);
> + cancel_delayed_work_sync(&hwrng_fill_dwork);
What if hwrng_manage_rngd races against hwrng_unregister?
Thanks,
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
