Messages in this thread | | | Date | Thu, 15 May 2014 11:21:06 +0200 | From | Christian König <> | Subject | Re: [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences |
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Am 15.05.2014 03:06, schrieb Maarten Lankhorst: > op 14-05-14 17:29, Christian König schreef: >>> + /* did fence get signaled after we enabled the sw irq? */ >>> + if >>> (atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq) >= >>> fence->seq) { >>> + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring); >>> + return false; >>> + } >>> + >>> + fence->fence_wake.flags = 0; >>> + fence->fence_wake.private = NULL; >>> + fence->fence_wake.func = radeon_fence_check_signaled; >>> + __add_wait_queue(&fence->rdev->fence_queue, &fence->fence_wake); >>> + fence_get(f); >> That looks like a race condition to me. The fence needs to be added >> to the wait queue before the check, not after. >> >> Apart from that the whole approach looks like a really bad idea to >> me. How for example is lockup detection supposed to happen with this? > It's not a race condition because fence_queue.lock is held when this > function is called. Ah, I see. That's also the reason why you moved the wake_up_all out of the processing function.
> > Lockup's a bit of a weird problem, the changes wouldn't allow core ttm > code to handle the lockup any more, > but any driver specific wait code would still handle this. I did this > by design, because in future patches the wait > function may be called from outside of the radeon driver. The official > wait function takes a timeout parameter, > so lockups wouldn't be fatal if the timeout is set to something like > 30*HZ for example, it would still return > and report that the function timed out. Timeouts help with the detection of the lockup, but not at all with the handling of them.
What we essentially need is a wait callback into the driver that is called in non atomic context without any locks held.
This way we can block for the fence to become signaled with a timeout and can then also initiate the reset handling if necessary.
The way you designed the interface now means that the driver never gets a chance to wait for the hardware to become idle and so never has the opportunity to the reset the whole thing.
Christian.
> > ~Maarten
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