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13afcb7ab3
There's a very small but existing uncertainty window when waking another thread up where it is possible for task_wakeup() not to wake the other task up because it's still running while this once is in the process of finishing and loses its TASK_RUNNING flag. In this case the wakeup will be missed. The problem is that we have a single flag to store 3 states, since the transition from running to sleeping isn't atomic. Thus we need to have another flag to cover this part. This patch introduces TASK_QUEUED to mention that the task is already in the run queue, running or not. This bit will be removed while TASK_RUNNING is kept once dequeued, and will be used when removing TASK_RUNNING to check if the task has been requeued. It might be possible to slightly improve this but the occurrence rate is quite low and we don't really need to complexify the scheduler to optimize for a rare case. The impact with the current code is very low since we have few inter- thread wakeups. Most of them are caused by checks killing sessions. This must be backported to 1.9. |
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