On Wed, Apr 11, 2018 at 04:22:13PM +0100, Alexandru Gheorghe wrote:
> vsyncworker::Routine assumes that when -EINTR is returned by
> WaitForSignalOrExitLocked the lock as been released, which is not
> true, so it hangs if a vsyncworker is never enabled and Exit is
> called.
>
> There are two code paths in WaitForSignalOrExitLocked that return
> -EINTR, one releases the lock the other doesn't.
> Looking at the clients of WaitForSignalOrExitLocked all assume the lock
> is still held, except vsyncworker::Routine.
> So, the proper fix needs two changes:
> - Make WaitForSignalOrExitLocked consistent and always hold the lock
> when exiting.
> - Release lock in vsynworker::Routine on all code paths.
>
> Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@xxxxxxx>
> ---
> vsyncworker.cpp | 1 +
> worker.cpp | 6 +++---
> 2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/vsyncworker.cpp b/vsyncworker.cpp
> index 3bfe4be..7c0c741 100644
> --- a/vsyncworker.cpp
> +++ b/vsyncworker.cpp
> @@ -120,6 +120,7 @@ void VSyncWorker::Routine() {
> if (!enabled_) {
> ret = WaitForSignalOrExitLocked();
> if (ret == -EINTR) {
> + Unlock();
> return;
> }
> }
> diff --git a/worker.cpp b/worker.cpp
> index da6c580..5b351e0 100644
> --- a/worker.cpp
> +++ b/worker.cpp
> @@ -66,13 +66,13 @@ int Worker::WaitForSignalOrExitLocked(int64_t max_nanoseconds) {
> ret = -ETIMEDOUT;
> }
>
> + // release leaves mutex locked when going out of scope
> + lk.release();
> +
> // exit takes precedence on timeout
> if (should_exit())
> ret = -EINTR;
>
> - // release leaves mutex locked when going out of scope
> - lk.release();
> -
I'm not sure why this chunk makes a difference? If the above was
"return -EINTR;" it would, but it's just assigning ret.
Sean
> return ret;
> }
>
> --
> 2.7.4
>
--
Sean Paul, Software Engineer, Google / Chromium OS
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