[PATCH v4 07/13] lib: test_hmm add ioctl to get zone device type
akpm at linux-foundation.org
Tue May 31 17:31:52 UTC 2022
On Tue, 31 May 2022 10:56:23 -0500 Alex Sierra <alex.sierra at amd.com> wrote:
> new ioctl cmd added to query zone device type. This will be
> used once the test_hmm adds zone device coherent type.
> @@ -1026,6 +1027,15 @@ static int dmirror_snapshot(struct dmirror *dmirror,
> return ret;
> +static int dmirror_get_device_type(struct dmirror *dmirror,
> + struct hmm_dmirror_cmd *cmd)
> + mutex_lock(&dmirror->mutex);
> + cmd->zone_device_type = dmirror->mdevice->zone_device_type;
> + mutex_unlock(&dmirror->mutex);
What does the locking here do?
Presumably cmd->zone_device_type can become out of date the instant the
mutex is released, so what was the point in taking the mutex?
And does it make sense to return potentially out-of-date info to
userspace? Perhaps this interface simply shouldn't exist?
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