2d8c1995b9
Dan Scales pointed out a theoretical deadlock in the runtime. The timer code runs timer functions while holding the timers lock for a P. The scavenger queues up a timer function that calls wakeScavenger, which acquires the scavenger lock. The scavengeSleep function acquires the scavenger lock, then calls resetTimer which can call addInitializedTimer which acquires the timers lock for the current P. So there is a potential deadlock, in that the scavenger lock and the timers lock for some P may both be acquired in different order. It's not clear to me whether this deadlock can ever actually occur. Issue 35532 describes another possible deadlock. The pollSetDeadline function acquires pd.lock for some poll descriptor, and in some cases calls resettimer which can in some cases acquire the timers lock for the current P. The timer code runs timer functions while holding the timers lock for a P. The timer function for poll descriptors winds up in netpolldeadlineimpl which acquires pd.lock. So again there is a potential deadlock, in that the pd lock for some poll descriptor and the timers lock for some P may both be acquired in different order. I think this can happen if we change the deadline for a network connection exactly as the former deadline expires. Looking at the code, I don't see any reason why we have to hold the timers lock while running a timer function. This CL implements that change. Updates #6239 Updates #27707 Fixes #35532 Change-Id: I17792f5a0120e01ea07cf1b2de8434d5c10704dd Reviewed-on: https://go-review.googlesource.com/c/go/+/207348 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Michael Knyszek <mknyszek@google.com> |
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