Fix deadlock in gofer direct IO.

Fixes several java runtime tests:
java/nio/channels/FileChannel/directio/ReadDirect.java
java/nio/channels/FileChannel/directio/PreadDirect.java

Updates #3576.

PiperOrigin-RevId: 328281849

pkg/sentry/fsimpl/gofer/regular_file.go

@@ -123,6 +123,10 @@ func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offs
 		return 0, io.EOF
 	}
 
+	var (
+		n       int64
+		readErr error
+	)
 	if fd.vfsfd.StatusFlags()&linux.O_DIRECT != 0 {
 		// Lock d.metadataMu for the rest of the read to prevent d.size from
 		// changing.
@@ -133,20 +137,25 @@ func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offs
 		if err := d.writeback(ctx, offset, dst.NumBytes()); err != nil {
 			return 0, err
 		}
-	}
-
-	rw := getDentryReadWriter(ctx, d, offset)
-	if fd.vfsfd.StatusFlags()&linux.O_DIRECT != 0 {
+		rw := getDentryReadWriter(ctx, d, offset)
 		// Require the read to go to the remote file.
 		rw.direct = true
+		n, readErr = dst.CopyOutFrom(ctx, rw)
+		putDentryReadWriter(rw)
+		if d.fs.opts.interop != InteropModeShared {
+			// Compare Linux's mm/filemap.c:do_generic_file_read() => file_accessed().
+			d.touchAtimeLocked(fd.vfsfd.Mount())
+		}
+	} else {
+		rw := getDentryReadWriter(ctx, d, offset)
+		n, readErr = dst.CopyOutFrom(ctx, rw)
+		putDentryReadWriter(rw)
+		if d.fs.opts.interop != InteropModeShared {
+			// Compare Linux's mm/filemap.c:do_generic_file_read() => file_accessed().
+			d.touchAtime(fd.vfsfd.Mount())
+		}
 	}
-	n, err := dst.CopyOutFrom(ctx, rw)
-	putDentryReadWriter(rw)
-	if d.fs.opts.interop != InteropModeShared {
-		// Compare Linux's mm/filemap.c:do_generic_file_read() => file_accessed().
-		d.touchAtime(fd.vfsfd.Mount())
-	}
-	return n, err
+	return n, readErr
 }
 
 // Read implements vfs.FileDescriptionImpl.Read.

pkg/sentry/fsimpl/gofer/time.go

@@ -52,6 +52,20 @@ func (d *dentry) touchAtime(mnt *vfs.Mount) {
 	mnt.EndWrite()
 }
 
+// Preconditions: d.metadataMu is locked. d.cachedMetadataAuthoritative() == true.
+func (d *dentry) touchAtimeLocked(mnt *vfs.Mount) {
+	if mnt.Flags.NoATime || mnt.ReadOnly() {
+		return
+	}
+	if err := mnt.CheckBeginWrite(); err != nil {
+		return
+	}
+	now := d.fs.clock.Now().Nanoseconds()
+	atomic.StoreInt64(&d.atime, now)
+	atomic.StoreUint32(&d.atimeDirty, 1)
+	mnt.EndWrite()
+}
+
 // Preconditions:
 // * d.cachedMetadataAuthoritative() == true.
 // * The caller has successfully called vfs.Mount.CheckBeginWrite().