[PATCH 1/2] hwrng: msm: add a spinlock and support for blocking reads

Timur Tabi
2018-06-22T15:41:11Z

On 6/22/18 10:38 AM, Stanimir Varbanov wrote:
> Before entering into the read function we already hold a mutex which
> serializes data reading so I cannot imagine how below sequence could
> happen. Can you explain how to reproduce this race?
>
>> 1. Core 1 reads status register, shows data is available.
>> 2. Core 2 also reads status register, same result
>> 3. Core 2 reads data register, depleting all entropy
>> 4. Core 1 reads data register, which returns 0

I have a test which spawns 100 copies of rngtest on a 48-core machine.
Without the spinlock, the driver returns no data much more often.

If there really is a mutex that serializes data reads across all cores,
then I don't have an explanation.