runtime: check held locks with staticlockranking

When lock ranking is enabled, we can now assert that lock preconditions
are met by checking that the caller holds required locks on function
entry.

This change adds the infrastructure to add assertions. Actual assertions
will be added for various locks in subsequent changes.

Some functions are protected by locks that are not directly accessible
in the function. In that case, we can use assertRankHeld to check that
any lock with the rank is held. This is less precise, but it avoids
requiring passing the lock into the functions.

Updates #40677

Change-Id: I843c6874867f975e90a063f087b6e2ffc147877b
Reviewed-on: https://go-review.googlesource.com/c/go/+/245484
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/runtime/lockrank_off.go b/src/runtime/lockrank_off.go
index 32378a9627..c04b61edc7 100644
--- a/src/runtime/lockrank_off.go
+++ b/src/runtime/lockrank_off.go
@@ -44,3 +44,11 @@ func releaseLockRank(rank lockRank) {
 //go:nosplit
 func lockWithRankMayAcquire(l *mutex, rank lockRank) {
 }
+
+//go:nosplit
+func assertLockHeld(l *mutex) {
+}
+
+//go:nosplit
+func assertRankHeld(r lockRank) {
+}