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Prevent file and goroutine leaks during self-hosted log tailing #828

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Merged
seanlinsley merged 3 commits into from
Jul 9, 2026
Merged

Prevent file and goroutine leaks during self-hosted log tailing #828

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89d7684
Prevent file descriptor and goroutine leaks in log tailing
seanlinsley Jul 8, 2026
43c7fba
Update go-tail to address deadlock on close
seanlinsley Jul 9, 2026
d9b5bf3
Add test coverage
seanlinsley Jul 9, 2026
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27 changes: 17 additions & 10 deletions input/system/selfhosted/logs.go
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Original file line number Diff line number Diff line change
Expand Up @@ -235,8 +235,16 @@ func tailFile(ctx context.Context, path string, out chan<- SelfHostedLogStreamIt
TailLoop:
for {
select {
case line := <-t.Lines():
out <- SelfHostedLogStreamItem{Line: line.String()}
case line, ok := <-t.Lines():
if !ok {
break TailLoop

@seanlinsley seanlinsley Jul 8, 2026

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The Lines channel could close due to an internal error. In that case we should break out of the loop to free the file descriptor

}
select {
case out <- SelfHostedLogStreamItem{Line: line.String()}:
case <-ctx.Done():

@seanlinsley seanlinsley Jul 8, 2026

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Check for context cancellation before writing to the out channel to avoid a possible deadlock

@lfittl lfittl Jul 8, 2026 •
edited
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Makes sense especially since that channel is currently unbuffered (and it seems beneficial to keep that, or at most use a low capacity, so that we backpressure on the actual file read in go-tail to avoid high memory use with large log lines).

prefixedLogger.PrintVerbose("Stopping log tail for %s (stop requested)", path)
break TailLoop
}
case <-ctx.Done():
prefixedLogger.PrintVerbose("Stopping log tail for %s (stop requested)", path)
break TailLoop
Expand Down Expand Up @@ -329,6 +337,12 @@ func setupLogLocationTail(ctx context.Context, logLocation string, out chan<- Se
return fmt.Errorf("fsnotify new: %s", err)
}

err = watcher.Add(logLocation)
if err != nil {
watcher.Close()
return fmt.Errorf("fsnotify add \"%s\": %s", logLocation, err)

@seanlinsley seanlinsley Jul 8, 2026

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watcher.Add is now before the goroutine launch so Add failures don't orphan the watcher goroutine and its open file tails.

}

go func() {
defer watcher.Close()
for {
Expand Down Expand Up @@ -358,7 +372,7 @@ func setupLogLocationTail(ctx context.Context, logLocation string, out chan<- Se
}
}
}
if event.Op&fsnotify.Remove == fsnotify.Remove || event.Op&fsnotify.Rename == fsnotify.Rename || event.Op&fsnotify.Chmod == fsnotify.Chmod {
if event.Op&fsnotify.Remove == fsnotify.Remove || event.Op&fsnotify.Rename == fsnotify.Rename {

@seanlinsley seanlinsley Jul 8, 2026

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Not related to the rest of the changes, but I'm not sure it makes sense to close the tail if the permissions change. At the very least we can end up losing in-progress logs.

@lfittl lfittl Jul 8, 2026

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Seems reasonable.

tailCancel, ok := openFiles[event.Name]
if ok {
tailCancel()
Expand All @@ -371,8 +385,6 @@ func setupLogLocationTail(ctx context.Context, logLocation string, out chan<- Se
case <-ctx.Done():
prefixedLogger.PrintVerbose("Log file fsnotify watcher received stop signal")
for fileName, tailCancel := range openFiles {
// TODO: This cancel might actually not be necessary since we are
// already canceling the parent context?
tailCancel()
delete(openFiles, fileName)
}
Expand All @@ -382,11 +394,6 @@ func setupLogLocationTail(ctx context.Context, logLocation string, out chan<- Se
}
}()

err = watcher.Add(logLocation)
if err != nil {
return fmt.Errorf("fsnotify add \"%s\": %s", logLocation, err)
}

return nil
}

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