Backport: tm: fix replmanager deadlock#6633
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deepthi merged 3 commits intovitessio:release-7.0from Aug 26, 2020
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And fix flaky test Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Change actionMutex to a semaphore to implement a tryLock function in tm, and use it in replManager. Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
Signed-off-by: Sugu Sougoumarane <ssougou@gmail.com>
deepthi
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Aug 26, 2020
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of #6625
A deadlock was found during a PRS. The root cause was a fix where we changed the replmanager to take the action lock. Otherwise, it would potentially race and conflict with other actions. But this led to a deadlock because PromoteReplica also waits for the replmanager to finish its fix.
We could have spot-fixed this for the specific use case. But in the interest of preventing other corner cases, the better fix was to change replmanager to not wait if it couldn't obtain a lock.
However, the implementation of lock with context timeout was flawed, because it wouldn't really timeout if the context expired. So, I implemented a new AcquireContext in sync2.Semaphore to, which encouraged to fix the flaky tests there.
Using the semaphore allowed me to implement a real tryLock, and replManager could use it.
Since this was a race condition, I tested it manually. The test that failed previously now passes.