[PATCH] dma-fence: add might_sleep annotation to _wait()

[Chris Wilson]

Quoting Daniel Vetter (2020-05-19 14:27:56)
> Do it uncontionally, there's a separate peek function with
> dma_fence_is_signalled() which can be called from atomic context.
> 
> v2: Consensus calls for an unconditional might_sleep (Chris,
> Christian)
> 
> Full audit:
> - dma-fence.h: Uses MAX_SCHEDULE_TIMOUT, good chance this sleeps
> - dma-resv.c: Timeout always at least 1
> - st-dma-fence.c: Save to sleep in testcases
> - amdgpu_cs.c: Both callers are for variants of the wait ioctl
> - amdgpu_device.c: Two callers in vram recover code, both right next
>   to mutex_lock.
> - amdgpu_vm.c: Use in the vm_wait ioctl, next to _reserve/unreserve
> - remaining functions in amdgpu: All for test_ib implementations for
>   various engines, caller for that looks all safe (debugfs, driver
>   load, reset)
> - etnaviv: another wait ioctl
> - habanalabs: another wait ioctl
> - nouveau_fence.c: hardcoded 15*HZ ... glorious
> - nouveau_gem.c: hardcoded 2*HZ ... so not even super consistent, but
>   this one does have a WARN_ON :-/ At least this one is only a
>   fallback path for when kmalloc fails. Maybe this should be put onto
>   some worker list instead, instead of a work per unamp ...
> - i915/selftests: Hardecoded HZ / 4 or HZ / 8
> - i915/gt/selftests: Going up the callchain looks safe looking at
>   nearby callers
> - i915/gt/intel_gt_requests.c. Wrapped in a mutex_lock
> - i915/gem_i915_gem_wait.c: The i915-version which is called instead
>   for i915 fences already has a might_sleep() annotation, so all good
> 
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Lucas Stach <l.stach at pengutronix.de>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Ben Skeggs <bskeggs at redhat.com>
> Cc: "VMware Graphics" <linux-graphics-maintainer at vmware.com>
> Cc: Oded Gabbay <oded.gabbay at gmail.com>
> Cc: linux-media at vger.kernel.org
> Cc: linaro-mm-sig at lists.linaro.org
> Cc: linux-rdma at vger.kernel.org
> Cc: amd-gfx at lists.freedesktop.org
> Cc: intel-gfx at lists.freedesktop.org
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Christian König <christian.koenig at amd.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  drivers/dma-buf/dma-fence.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 90edf2b281b0..656e9ac2d028 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -208,6 +208,8 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
>         if (WARN_ON(timeout < 0))
>                 return -EINVAL;
>  
> +       might_sleep();

git grep matches your synopsis.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris