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runtime: replace rwmutexR/W with per-rwmutex lock rank
CL 549536 intended to decouple the internal implementation of rwmutex from the semantic meaning of an rwmutex read/write lock in the static lock ranking. Unfortunately, it was not thought through well enough. The internals were represented with the rwmutexR and rwmutexW lock ranks. The idea was that the internal lock ranks need not model the higher-level ordering, since those have separate rankings. That is incorrect; rwmutexW is held for the duration of a write lock, so it must be ranked before any lock taken while any write lock is held, which is precisely what we were trying to avoid. This is visible in violations like: 0 : execW 11 0x0 1 : rwmutexW 51 0x111d9c8 2 : fin 30 0x111d3a0 fatal error: lock ordering problem execW < fin is modeled, but rwmutexW < fin is missing. Fix this by eliminating the rwmutexR/W lock ranks shared across different types of rwmutex. Instead require users to define an additional "internal" lock rank to represent the implementation details of rwmutex.rLock. We can avoid an additional "internal" lock rank for rwmutex.wLock because the existing writeRank has the same semantics for semantic and internal locking. i.e., writeRank is held for the duration of a write lock, which is exactly how rwmutex.wLock is used, so we can use writeRank directly on wLock. For #64722. Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-staticlockranking Change-Id: Ia572de188a46ba8fe054ae28537648beaa16b12c Reviewed-on: https://go-review.googlesource.com/c/go/+/555055 LUCI-TryBot-Result: Go LUCI <[email protected]> Reviewed-by: Michael Knyszek <[email protected]>
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‎src/runtime/export_test.go‎

Lines changed: 1 addition & 1 deletion
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@@ -587,7 +587,7 @@ type RWMutex struct {
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}
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func (rw *RWMutex) Init() {
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rw.rw.init(lockRankTestR, lockRankTestW)
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rw.rw.init(lockRankTestR, lockRankTestRInternal, lockRankTestW)
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}
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func (rw *RWMutex) RLock() {

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