[PATCH 4.18 139/228] intel_th: Fix device removal logic

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>

commit 8801922cd94c918e4dc3a108ecaa500c4d40583f upstream.

Commit a753bfcfdb1f ("intel_th: Make the switch allocate its subdevices")
brings in new subdevice addition/removal logic that's broken for "host
mode": the SWITCH device has no children to begin with, which is not
handled in the code. This results in a null dereference bug later down
the path.

This patch fixes the subdevice removal code to handle host mode correctly.

Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Fixes: a753bfcfdb1f ("intel_th: Make the switch allocate its subdevices")
CC: stable@xxxxxxxxxxxxxxx # v4.14+
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/hwtracing/intel_th/core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/hwtracing/intel_th/core.c
+++ b/drivers/hwtracing/intel_th/core.c
@@ -139,7 +139,8 @@ static int intel_th_remove(struct device
 			th->thdev[i] = NULL;
 		}
 
-		th->num_thdevs = lowest;
+		if (lowest >= 0)
+			th->num_thdevs = lowest;
 	}
 
 	if (thdrv->attr_group)