Messages in this thread | | | Date | Thu, 15 May 2014 03:06:37 +0200 | From | Maarten Lankhorst <> | Subject | Re: [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences |
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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.
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.
~Maarten -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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