• Austin Clements's avatar
    runtime: fix hangs in TestDebugCall* · a27f3d5c
    Austin Clements authored
    This fixes a few different issues that led to hangs and general
    flakiness in the TestDebugCall* tests.
    
    1. This fixes missing wake-ups in two error paths of the SIGTRAP
       signal handler. If the goroutine was in an unknown state, or if
       there was an unknown debug call status, we currently don't wake the
       injection coordinator. These are terminal states, so this resulted
       in a hang.
    
    2. This adds a retry if the target goroutine is in a transient state
       that prevents us from injecting a call. The most common failure
       mode here is that the target goroutine is in _Grunnable, but this
       was previously masked because it deadlocked the test.
    
    3. Related to 2, this switches the "ready" signal from the target
       goroutine from a blocking channel send to a non-blocking channel
       send. This makes it much less likely that we'll catch this
       goroutine while it's in the runtime performing that send.
    
    4. This increases GOMAXPROCS from 2 to 8 during these tests. With the
       current setting of 2, we can have at most the non-preemptible
       goroutine we're injecting a call in to and the goroutine that's
       trying to make it exit. If anything else comes along, it can
       deadlock. One particular case I observed was in TestDebugCallGC,
       where runtime.GC() returns before the forEachP that prepares
       sweeping on all goroutines has finished. When this happens, the
       forEachP blocks on the non-preemptible loop, which means we now
       have at least three goroutines that need to run.
    
    Fixes #25519.
    
    Updates #29124.
    
    Change-Id: I7bc41dc0b865b7d0bb379cb654f9a1218bc37428
    Reviewed-on: https://go-review.googlesource.com/c/154112
    Run-TryBot: Austin Clements <austin@google.com>
    Reviewed-by: 's avatarMichael Knyszek <mknyszek@google.com>
    a27f3d5c
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