sync: panic rather than throw on nil *Pool

Fixes #61651

Change-Id: I27d581719e6bf38910f9d47dcf023bbff74ddf72
Reviewed-on: https://go-review.googlesource.com/c/go/+/514037
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/sync/pool.go b/src/sync/pool.go
index cf01e2e189..ffab67bf19 100644
--- a/src/sync/pool.go
+++ b/src/sync/pool.go
@@ -196,6 +196,13 @@ func (p *Pool) getSlow(pid int) any {
 // returns poolLocal pool for the P and the P's id.
 // Caller must call runtime_procUnpin() when done with the pool.
 func (p *Pool) pin() (*poolLocal, int) {
+	// Check whether p is nil to get a panic.
+	// Otherwise the nil dereference happens while the m is pinned,
+	// causing a fatal error rather than a panic.
+	if p == nil {
+		panic("nil Pool")
+	}
+
 	pid := runtime_procPin()
 	// In pinSlow we store to local and then to localSize, here we load in opposite order.
 	// Since we've disabled preemption, GC cannot happen in between.