From 577bb3d0ce576b2ca311e58dd942f189838b80fc Mon Sep 17 00:00:00 2001 From: Michael Pratt Date: Fri, 14 Mar 2025 10:50:25 -0400 Subject: runtime: only set isExtraInC if there are no Go frames left mp.isExtraInC is intended to indicate that this M has no Go frames at all; it is entirely executing in C. If there was a cgocallback to Go and then a cgocall to C, such that the leaf frames are C, that is fine. e.g., traceback can handle this fine with SetCgoTraceback (or by simply skipping the C frames). However, we currently mismanage isExtraInC, unconditionally setting it on return from cgocallback. This means that if there are two levels of cgocallback, we end up running Go code with isExtraInC set. 1. C-created thread calls into Go function 1 (via cgocallback). 2. Go function 1 calls into C function 1 (via cgocall). 3. C function 1 calls into Go function 2 (via cgocallback). 4. Go function 2 returns back to C function 1 (returning via the remainder of cgocallback). 5. C function 1 returns back to Go function 1 (returning via the remainder of cgocall). 6. Go function 1 is now running with mp.isExtraInC == true. The fix is simple; only set isExtraInC on return from cgocallback if there are no more Go frames. There can't be more Go frames unless there is an active cgocall out of the Go frames. Fixes #72870. Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest Change-Id: I6a6a636c4e7ba75a29639d7036c5af3738033467 Reviewed-on: https://go-review.googlesource.com/c/go/+/658035 Reviewed-by: Cherry Mui Commit-Queue: Michael Pratt Auto-Submit: Michael Pratt Reviewed-by: Michael Knyszek LUCI-TryBot-Result: Go LUCI --- src/runtime/runtime2.go | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/runtime/runtime2.go') diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go index 0c70d2cc81..6b9f49d503 100644 --- a/src/runtime/runtime2.go +++ b/src/runtime/runtime2.go @@ -554,7 +554,7 @@ type m struct { printlock int8 incgo bool // m is executing a cgo call isextra bool // m is an extra m - isExtraInC bool // m is an extra m that is not executing Go code + isExtraInC bool // m is an extra m that does not have any Go frames isExtraInSig bool // m is an extra m in a signal handler freeWait atomic.Uint32 // Whether it is safe to free g0 and delete m (one of freeMRef, freeMStack, freeMWait) needextram bool -- cgit v1.3