2520e72d3b
As a cleanup, golang.org/cl/307914 unintentionally caused the idle GC work recheck to drop sched.lock between acquiring a P and committing to keep it (once a worker G was found). This is unsafe, as releasing a P requires extra checks once sched.lock is taken (such as for runSafePointFn). Since checkIdleGCNoP does not perform these extra checks, we can now race with other users. In the case of #45975, we may hang with this sequence: 1. M1: checkIdleGCNoP takes sched.lock, gets P1, releases sched.lock. 2. M2: forEachP takes sched.lock, iterates over sched.pidle without finding P1, releases sched.lock. 3. M1: checkIdleGCNoP puts P1 back in sched.pidle. 4. M2: forEachP waits forever for P1 to run the safePointFn. Change back to the old behavior of releasing sched.lock only after we are certain we will keep the P. Thus if we put it back its removal from sched.pidle was never visible. Fixes #45975 For #45916 For #45885 For #45884 Change-Id: I191a1800923b206ccaf96bdcdd0bfdad17b532e9 Reviewed-on: https://go-review.googlesource.com/c/go/+/318569 Trust: Michael Pratt <mpratt@google.com> Run-TryBot: Michael Pratt <mpratt@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com> |
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