Ensure fsimpl/gofer.dentryPlatformFile.hostFileMapper is initialized.

Fixes #1812. (The more direct cause of the deadlock is panic unsafety because
the historically high cost of defer means that we avoid it in hot paths,
including much of MM; defer is much cheaper as of Go 1.14, but still a
measurable overhead.)

PiperOrigin-RevId: 294560316

1 files changed, 5 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index 8e11e06b3..54c1031a7 100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -571,6 +571,8 @@ func (fd *regularFileFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpt
 	default:
 		panic(fmt.Sprintf("unknown InteropMode %v", d.fs.opts.interop))
 	}
+	// After this point, d may be used as a memmap.Mappable.
+	d.pf.hostFileMapperInitOnce.Do(d.pf.hostFileMapper.Init)
 	return vfs.GenericConfigureMMap(&fd.vfsfd, d, opts)
 }
 
@@ -799,6 +801,9 @@ type dentryPlatformFile struct {
 	// If this dentry represents a regular file, and handle.fd >= 0,
 	// hostFileMapper caches mappings of handle.fd.
 	hostFileMapper fsutil.HostFileMapper
+
+	// hostFileMapperInitOnce is used to lazily initialize hostFileMapper.
+	hostFileMapperInitOnce sync.Once
 }
 
 // IncRef implements platform.File.IncRef.