From 22e57c6655288e129fa807eecf936fdf5ac2ced8 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Thu, 19 Nov 2015 13:26:43 -0500 Subject: [PATCH] runtime: make stack barrier locking more robust The stack barrier locking functions use a simple cas lock because they need to support trylock, but currently don't increment g.m.locks. This is okay right now because they always run on the system stack or the signal stack and are hence non-preemtible, but this could lead to difficult-to-reproduce deadlocks if these conditions change in the future. Make these functions more robust by incrementing g.m.locks and making them nosplit to enforce non-preemtibility. Change-Id: I73d60a35bd2ad2d81c73aeb20dbd37665730eb1b Reviewed-on: https://go-review.googlesource.com/17058 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Ingo Oeser Reviewed-by: Russ Cox --- src/runtime/mstkbar.go | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/src/runtime/mstkbar.go b/src/runtime/mstkbar.go index 6f5b459853..1c1c2eaf0a 100644 --- a/src/runtime/mstkbar.go +++ b/src/runtime/mstkbar.go @@ -300,16 +300,26 @@ func setNextBarrierPC(pc uintptr) { // This is necessary because a sigprof during barrier installation or // removal could observe inconsistencies between the stkbar array and // the stack itself and crash. +// +//go:nosplit func gcLockStackBarriers(gp *g) { + acquirem() for !atomic.Cas(&gp.stackLock, 0, 1) { osyield() } } +//go:nosplit func gcTryLockStackBarriers(gp *g) bool { - return atomic.Cas(&gp.stackLock, 0, 1) + mp := acquirem() + result := atomic.Cas(&gp.stackLock, 0, 1) + if !result { + releasem(mp) + } + return result } func gcUnlockStackBarriers(gp *g) { atomic.Store(&gp.stackLock, 0) + releasem(getg().m) } -- 2.50.0