fix goroutine leaks in events and logs backend

When running a single podman logs this is not really important since we
will exit when we finish reading the logs. However for the system
service this is very important. Leaking goroutines will cause an
increased memory and CPU ussage over time.

Both the the event and log backend have goroutine leaks with both the
file and journald drivers.

The journald backend has the problem that journal.Wait(IndefiniteWait)
will block until we get a new journald event. So when a client closes
the connection the goroutine would still wait until there is a new
journal entry. To fix this we just wait for a maximum of 5 seconds,
after that we can check if the client connection was closed and exit
correctly in this case.

For the file backend we can fix this by waiting for either the log line
or context cancel at the same time. Currently it would block waiting for
new log lines and only check afterwards if the client closed the
connection and thus hang forever if there are no new log lines.

[NO NEW TESTS NEEDED] I am open to ideas how we can test memory leaks in
CI.
To test manually run a container like this:
`podman run --log-driver $driver  --name test -d alpine sh -c 'i=1; while [ "$i" -ne 1000 ]; do echo "line $i"; i=$((i + 1)); done; sleep inf'`
where `$driver` can be either `journald` or `k8s-file`.
Then start the podman system service and use:
`curl -m 1 --output -  --unix-socket $XDG_RUNTIME_DIR/podman/podman.sock -v 'http://d/containers/test/logs?follow=1&since=0&stderr=1&stdout=1' &>/dev/null`
to get the logs from the API and then it closes the connection after 1 second.
Now run the curl command several times and check the memory usage of the service.

Fixes #14879

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

libpod/container_log.go

@@ -10,6 +10,7 @@ import (
 	"github.com/containers/podman/v4/libpod/define"
 	"github.com/containers/podman/v4/libpod/events"
 	"github.com/containers/podman/v4/libpod/logs"
+	"github.com/nxadm/tail"
 	"github.com/nxadm/tail/watch"
 	"github.com/sirupsen/logrus"
 )
@@ -74,14 +75,19 @@ func (c *Container) readFromLogFile(ctx context.Context, options *logs.LogOption
 
 	go func() {
 		defer options.WaitGroup.Done()
-
+		var line *tail.Line
-		for line := range t.Lines {
+		var ok bool
+		for {
 			select {
 			case <-ctx.Done():
 				// the consumer has cancelled
+				t.Kill(errors.New("hangup by client"))
 				return
-			default:
+			case line, ok = <-t.Lines:
-				// fallthrough
+				if !ok {
+					// channel was closed
+					return
+				}
 			}
 			nll, err := logs.NewLogLine(line.Text)
 			if err != nil {

libpod/container_log_linux.go

@@ -178,8 +178,13 @@ func (c *Container) readFromJournal(ctx context.Context, options *logs.LogOption
 				if !options.Follow || !containerCouldBeLogging {
 					return
 				}
-				// Sleep until something's happening on the journal.
+
-				journal.Wait(sdjournal.IndefiniteWait)
+				// journal.Wait() is blocking, this would cause the goroutine to hang forever
+				// if no more journal entries are generated and thus if the client
+				// has closed the connection in the meantime to leak memory.
+				// Waiting only 5 seconds makes sure we can check if the client closed in the
+				// meantime at least every 5 seconds.
+				journal.Wait(5 * time.Second)
 				continue
 			}
 			lastReadCursor = cursor

libpod/events/journal_linux.go

@@ -141,9 +141,18 @@ func (e EventJournalD) Read(ctx context.Context, options ReadOptions) error {
 			if !options.Stream || (len(options.Until) > 0 && time.Now().After(untilTime)) {
 				break
 			}
-			t := sdjournal.IndefiniteWait
+
+			// j.Wait() is blocking, this would cause the goroutine to hang forever
+			// if no more journal entries are generated and thus if the client
+			// has closed the connection in the meantime to leak memory.
+			// Waiting only 5 seconds makes sure we can check if the client closed in the
+			// meantime at least every 5 seconds.
+			t := 5 * time.Second
 			if len(options.Until) > 0 {
-				t = time.Until(untilTime)
+				until := time.Until(untilTime)
+				if until < t {
+					t = until
+				}
 			}
 			_ = j.Wait(t)
 			continue

libpod/events/logfile.go

@@ -108,23 +108,19 @@ func (e EventLogFile) Read(ctx context.Context, options ReadOptions) error {
 			}
 		}()
 	}
-	funcDone := make(chan bool)
+	var line *tail.Line
-	copy := true
+	var ok bool
-	go func() {
+	for {
-		select {
-		case <-funcDone:
-			// Do nothing
-		case <-ctx.Done():
-			copy = false
-			t.Kill(errors.New("hangup by client"))
-		}
-	}()
-	for line := range t.Lines {
 		select {
 		case <-ctx.Done():
 			// the consumer has cancelled
+			t.Kill(errors.New("hangup by client"))
 			return nil
-		default:
+		case line, ok = <-t.Lines:
+			if !ok {
+				// channel was closed
+				return nil
+			}
 			// fallthrough
 		}
 
@@ -138,12 +134,10 @@ func (e EventLogFile) Read(ctx context.Context, options ReadOptions) error {
 		default:
 			return fmt.Errorf("event type %s is not valid in %s", event.Type.String(), e.options.LogFilePath)
 		}
-		if copy && applyFilters(event, filterMap) {
+		if applyFilters(event, filterMap) {
 			options.EventChannel <- event
 		}
 	}
-	funcDone <- true
-	return nil
 }
 
 // String returns a string representation of the logger