[dev.fuzz] internal/fuzz: fix race in worker RPC logic

We want worker RPCs to return as soon as the context is cancelled,
which happens if the user presses ^C, we hit the time limit, or
another worker discovers a crasher. RPCs typically block when reading
pipes: the server waits for call arguments from the client, and the
client waits for results from the server.

Since io.Reader.Read doesn't accept a context.Context and reads on
pipe file descriptors are difficult to reliably unblock, we've done
this by calling Read in a goroutine, and returning from the parent
function when ctx.Done() is closed, even if the underlying goroutine
isn't finished.

In workerServer.serve, we also called the fuzz function in the same
goroutine. This resulted in a bug: serve could return while the fuzz
function was still running. The fuzz function could observe side
effects from cleanup functions registered with F.Cleanup.

This change refactors read cancellation logic into contextReader. Only
the underlying Read is done in a goroutine. workerServe.serve won't
return while the fuzz function is running.

Fixes #46632

Change-Id: Id1ed31f6521155c7c8e76dd52a2d70aa93cab201
Reviewed-on: https://go-review.googlesource.com/c/go/+/329920
Trust: Jay Conrod <jayconrod@google.com>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>

0 files changed, 0 insertions, 0 deletions