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Close eventfd shutdown/wakeup race by closely tracking epoll edges #9586

Merged
merged 3 commits into from Sep 23, 2019
Merged

Close eventfd shutdown/wakeup race by closely tracking epoll edges #9586

merged 3 commits into from Sep 23, 2019

Commits on Sep 20, 2019

  1. Close eventfd shutdown/wakeup race by closely tracking epoll edges 

    Motivation

This is another iteration of #9476.

Modifications

Instead of maintaining a count of all writes performed and then using
reads during shutdown to ensure all are accounted for, just set a flag
after each write and don't reset it until the corresponding event has
been returned from epoll_wait.

This requires that while a write is still pending we don't reset
wakenUp, i.e. continue to block writes from the wakeup() method.

Result

Race condition eliminated. Fixes #9362

Co-authored-by: Norman Maurer <norman_maurer@apple.com>
    @njhill @normanmaurer
    njhill and normanmaurer committed Sep 20, 2019
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  2. Use volatile store to reset wakenUp field; add log for missed evfd write

    @njhill
    njhill committed Sep 20, 2019
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  3. Don't use timerfd for epollWaitTimeboxed()

    @njhill
    njhill committed Sep 20, 2019
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