957259b7e2
On Windows, we implement asynchronous preemption using SuspendThread to suspend other threads in our process. However, SuspendThread is itself actually asynchronous (it enqueues a kernel "asynchronous procedure call" and returns). Unfortunately, Windows' ExitProcess API kills all threads except the calling one and then runs APCs. As a result, if SuspendThread and ExitProcess are called simultaneously, the exiting thread can be suspended and the suspending thread can be exited, leaving behind a ghost process consisting of a single thread that's suspended. We've already protected against the runtime's own calls to ExitProcess, but if Go code calls external code, there's nothing stopping that code from calling ExitProcess. For example, in #35775, our own call to racefini leads to C code calling ExitProcess and occasionally causing a deadlock. This CL fixes this by introducing synchronization between calling external code on Windows and preemption. It adds an atomic field to the M that participates in a simple CAS-based synchronization protocol to prevent suspending a thread running external code. We use this to protect cgocall (which is used for both cgo calls and system calls on Windows) and racefini. Tested by running the flag package's TestParse test compiled in race mode in a loop. Before this change, this would reliably deadlock after a few minutes. Fixes #35775. Updates #10958, #24543. Change-Id: I50d847abcdc2688b4f71eee6a75eca0f2fee892c Reviewed-on: https://go-review.googlesource.com/c/go/+/213837 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Cherry Zhang <cherryyz@google.com> Reviewed-by: David Chase <drchase@google.com> |
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