Port aio to VFS2.

In order to make sure all aio goroutines have stopped during S/R, a new
WaitGroup was added to TaskSet, analagous to runningGoroutines. This WaitGroup
is incremented with each aio goroutine, and waited on during kernel.Pause.

The old VFS1 aio code was changed to use this new WaitGroup, rather than
fs.Async. The only uses of fs.Async are now inode and mount Release operations,
which do not call fs.Async recursively. This fixes a lock-ordering violation
that can cause deadlocks.

Updates #1035.

PiperOrigin-RevId: 316689380

1 files changed, 7 insertions, 0 deletions

diff --git a/pkg/sentry/kernel/threads.go b/pkg/sentry/kernel/threads.go
index bf2dabb6e..872e1a82d 100644
--- a/pkg/sentry/kernel/threads.go
+++ b/pkg/sentry/kernel/threads.go
@@ -87,6 +87,13 @@ type TaskSet struct {
 	// at time of save (but note that this is not necessarily the same thing as
 	// sync.WaitGroup's zero value).
 	runningGoroutines sync.WaitGroup `state:"nosave"`
+
+	// aioGoroutines is the number of goroutines running async I/O
+	// callbacks.
+	//
+	// aioGoroutines is not saved but is required to be zero at the time of
+	// save.
+	aioGoroutines sync.WaitGroup `state:"nosave"`
 }
 
 // newTaskSet returns a new, empty TaskSet.