Annoying AMD Linux Graphics Driver Crashes With "Timed Out Fences" Has A Fix Coming

Since the Linux 5.19 kernel there have been many reports on Twitter, Reddit, or forums, and elsewhere over open-source AMD Radeon driver users experiencing crashes that often then appear in the kernel log around fences timing out. A fix for this show-stopping bug for AMD gamers looks like it will be coming to the Linux 6.2 kernel.

Over the past several months have been a number of complaints around the AMDGPU driver crashing and in common with these bug reports since Linux 5.19 has been seeing "*ERROR* Waiting for fences timed out!" messages. There's been quite a number of AMD Radeon Linux users reporting such problems since Linux 5.19 particularly when running demanding games with modern Radeon RX GPUs.

AMD engineers had a tough time surprisingly reproducing the problem but they now have and there are some patches pending believed to fix this problem.

Longtime AMD Linux graphics driver developer Christian König was finally able to reproduce the problem locally and quickly whipped up some pending patches. The patches introduce a new "DRM_SCHED_FENCE_DONT_PIPELINE" flag that prevents pipelining of jobs depending upon this fence and then goes ahead and makes use of this new flag for VM updates. This ensures there is always a CPU round-trip to let the submission code decide correctly whether a TLB flush is needed. This in turn appears to take care of these annoying problems since Linux 5.19.

These patches were pushed to "amd-staging-drm-next", which is code set for DRM-Next. Thus it looks like this new code won't be merged until the Linux 6.2 merge window while we'll see after that if it ends up being back-ported to earlier kernel stable series.

Among criticism of this bug elsewhere, there is a lengthy bug ticket where over the past three months many users have been voicing the problem and ultimately where the fix was announced.