From 2fb4b6ace860a485be8afdf3ed523ab5f1f616c8 Mon Sep 17 00:00:00 2001
From: Erik Schilling <erik.schilling@linaro.org>
Date: Fri, 7 Jul 2023 12:23:28 +0200
Subject: [PATCH] tree-wide: continue unwinds on join failures

The error from joining a thread is a bit confusing. It is only printed
if the other thread panicked. This means, effectively, we only get here
if something called .unwrap(), .expect() or panicked in a different way.
In these cases an (ugly) error was already printend. Printing a pretty
message about the join failure does not really help a lot...

So let's just continue the unwind as suggested by the docs on the join
`Result` [1].

Before:

    thread '<unnamed>' panicked at 'Test panic', crates/gpio/src/backend.rs:146:13
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
    thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Any { .. }', crates/gpio/src/backend.rs:176:23

After:

    thread '<unnamed>' panicked at 'Test panic', crates/gpio/src/backend.rs:146:13
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[1]: https://doc.rust-lang.org/std/thread/type.Result.html

Signed-off-by: Erik Schilling <erik.schilling@linaro.org>
---
 vhost-device-gpio/src/backend.rs | 4 +---
 vhost-device-i2c/src/main.rs     | 4 +---
 vhost-device-rng/src/main.rs     | 4 +---
 vhost-device-vsock/src/main.rs   | 7 ++++++-
 4 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/vhost-device-gpio/src/backend.rs b/vhost-device-gpio/src/backend.rs
index e1e28152d..42dbdfc10 100644
--- a/vhost-device-gpio/src/backend.rs
+++ b/vhost-device-gpio/src/backend.rs
@@ -36,8 +36,6 @@ pub(crate) enum Error {
     DeviceDuplicate(u32),
     #[error("Failed while parsing to integer: {0:?}")]
     ParseFailure(ParseIntError),
-    #[error("Failed to join threads")]
-    FailedJoiningThreads,
     #[error("Could not open gpio device: {0}")]
     CouldNotOpenDevice(crate::gpio::Error),
     #[error("Could not create gpio controller: {0}")]
@@ -227,7 +225,7 @@ fn start_backend(args: GpioArgs) -> Result<()> {
     }
 
     for handle in handles {
-        handle.join().map_err(|_| Error::FailedJoiningThreads)??;
+        handle.join().map_err(std::panic::resume_unwind).unwrap()?;
     }
 
     Ok(())
diff --git a/vhost-device-i2c/src/main.rs b/vhost-device-i2c/src/main.rs
index eb838a09a..5b2712ffa 100644
--- a/vhost-device-i2c/src/main.rs
+++ b/vhost-device-i2c/src/main.rs
@@ -39,8 +39,6 @@ pub(crate) enum Error {
     I2cFailure(i2c::Error),
     #[error("Failed while parsing to integer: {0:?}")]
     ParseFailure(ParseIntError),
-    #[error("Failed to join threads")]
-    FailedJoiningThreads,
     #[error("Could not create backend: {0}")]
     CouldNotCreateBackend(vhu_i2c::Error),
     #[error("Could not create daemon: {0}")]
@@ -215,7 +213,7 @@ fn start_backend<D: 'static + I2cDevice + Send + Sync>(args: I2cArgs) -> Result<
     }
 
     for handle in handles {
-        handle.join().map_err(|_| Error::FailedJoiningThreads)??;
+        handle.join().map_err(std::panic::resume_unwind).unwrap()?;
     }
 
     Ok(())
diff --git a/vhost-device-rng/src/main.rs b/vhost-device-rng/src/main.rs
index b639aa528..a0e09a292 100644
--- a/vhost-device-rng/src/main.rs
+++ b/vhost-device-rng/src/main.rs
@@ -33,8 +33,6 @@ pub(crate) enum Error {
     InvalidPeriodInput(u128),
     #[error("Wrong socket count: {0}")]
     InvalidSocketCount(u32),
-    #[error("Threads can't be joined")]
-    FailedJoiningThreads,
     #[error("Could not create backend: {0}")]
     CouldNotCreateBackend(std::io::Error),
     #[error("Could not create daemon: {0}")]
@@ -139,7 +137,7 @@ pub(crate) fn start_backend(config: VuRngConfig) -> Result<()> {
     }
 
     for handle in handles {
-        handle.join().map_err(|_| Error::FailedJoiningThreads)??;
+        handle.join().map_err(std::panic::resume_unwind).unwrap()?;
     }
 
     Ok(())
diff --git a/vhost-device-vsock/src/main.rs b/vhost-device-vsock/src/main.rs
index 293779e10..d8858df11 100644
--- a/vhost-device-vsock/src/main.rs
+++ b/vhost-device-vsock/src/main.rs
@@ -281,7 +281,12 @@ pub(crate) fn start_backend_servers(configs: &[VsockConfig]) -> Result<(), Backe
 
     while !handles.is_empty() {
         let thread_id = receiver.recv().unwrap();
-        handles.remove(&thread_id).unwrap().join().unwrap()?;
+        handles
+            .remove(&thread_id)
+            .unwrap()
+            .join()
+            .map_err(std::panic::resume_unwind)
+            .unwrap()?;
     }
 
     Ok(())