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Subject: Re: [PATCH] dma-fence: add might_sleep annotation to _wait()
To:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        DRI Development <dri-devel@lists.freedesktop.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Lucas Stach <l.stach@pengutronix.de>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Ben Skeggs <bskeggs@redhat.com>,
        VMware Graphics <linux-graphics-maintainer@vmware.com>,
        Oded Gabbay <oded.gabbay@gmail.com>,
        linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
        linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Daniel Vetter <daniel.vetter@intel.com>
References: <20200519132756.682888-1-daniel.vetter@ffwll.ch>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Am 19.05.20 um 15:27 schrieb Daniel Vetter:
> 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@amd.com>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: "VMware Graphics" <linux-graphics-maintainer@vmware.com>
> Cc: Oded Gabbay <oded.gabbay@gmail.com>
> Cc: linux-media@vger.kernel.org
> Cc: linaro-mm-sig@lists.linaro.org
> Cc: linux-rdma@vger.kernel.org
> Cc: amd-gfx@lists.freedesktop.org
> Cc: intel-gfx@lists.freedesktop.org
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Reviewed-by: Christian König <christian.koenig@amd.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();
> +
>   	trace_dma_fence_wait_start(fence);
>   	if (fence->ops->wait)
>   		ret = fence->ops->wait(fence, intr, timeout);