On Thu, Jul 29, 2021 at 9:52 PM John Stultz [off-list ref] wrote:

On Thu, Jul 29, 2021 at 12:24 AM Daniel Vetter [off-list ref] wrote:

quoted

On Thu, Jul 29, 2021 at 09:03:30AM +0200, Christian König wrote:

quoted

As we now knew controlling dma_fence synchronization from userspace is
extremely dangerous and can not only deadlock drivers but trivially also the
whole kernel memory management.

Entirely remove this option. We now have in kernel unit tests to exercise the
dma_fence framework and it's containers.

Signed-off-by: Christian König <christian.koenig@amd.com>

There's also igts for this, and Android heavily uses this. So I'm not sure
we can just nuke it.

Eeeeh... I don't think that's actually the case anymore. As of
android12-5.10 CONFIG_SW_SYNC is not turned on.
Further, Android is disabling debugfs in their kernels as it exposes
too much to userland.

That said, there still are some references to it:
  https://cs.android.com/android/platform/superproject/+/master:system/core/libsync/sync.c;l=416

Hello,

Like John mentioned, CONFIG_SW_SYNC is not turned on for the *-5.4 and
newer branches in the Android Common Kernel. The references in AOSP
are only in place to support devices with older kernels upgrading to
newer Android versions.

Regards,
Hridya

But it looks like the actual users are only kselftest and igt?

Adding Alistair, Hridya and Sandeep in case they have more context.

thanks
-john