This is a note to let you know that I've just added the patch titled
usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
usb-ohci-proper-handling-of-ed_rm_list-to-handle-race-condition-between-usb_kill_urb-and-finish_unlinks.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 46408ea558df13b110e0866b99624384a33bdeba Mon Sep 17 00:00:00 2001
From: AMAN DEEP <aman.deep@xxxxxxxxxxx>
Date: Thu, 8 Feb 2018 11:55:01 +0800
Subject: usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()
From: AMAN DEEP <aman.deep@xxxxxxxxxxx>
commit 46408ea558df13b110e0866b99624384a33bdeba upstream.
There is a race condition between finish_unlinks->finish_urb() function
and usb_kill_urb() in ohci controller case. The finish_urb calls
spin_unlock(&ohci->lock) before usb_hcd_giveback_urb() function call,
then if during this time, usb_kill_urb is called for another endpoint,
then new ed will be added to ed_rm_list at beginning for unlink, and
ed_rm_list will point to newly added.
When finish_urb() is completed in finish_unlinks() and ed->td_list
becomes empty as in below code (in finish_unlinks() function):
if (list_empty(&ed->td_list)) {
*last = ed->ed_next;
ed->ed_next = NULL;
} else if (ohci->rh_state == OHCI_RH_RUNNING) {
*last = ed->ed_next;
ed->ed_next = NULL;
ed_schedule(ohci, ed);
}
The *last = ed->ed_next will make ed_rm_list to point to ed->ed_next
and previously added ed by usb_kill_urb will be left unreferenced by
ed_rm_list. This causes usb_kill_urb() hang forever waiting for
finish_unlink to remove added ed from ed_rm_list.
The main reason for hang in this race condtion is addition and removal
of ed from ed_rm_list in the beginning during usb_kill_urb and later
last* is modified in finish_unlinks().
As suggested by Alan Stern, the solution for proper handling of
ohci->ed_rm_list is to remove ed from the ed_rm_list before finishing
any URBs. Then at the end, we can add ed back to the list if necessary.
This properly handle the updated ohci->ed_rm_list in usb_kill_urb().
Fixes: 977dcfdc6031 ("USB: OHCI: don't lose track of EDs when a controller dies")
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
CC: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Aman Deep <aman.deep@xxxxxxxxxxx>
Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/host/ohci-q.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
--- a/drivers/usb/host/ohci-q.c
+++ b/drivers/usb/host/ohci-q.c
@@ -1018,6 +1018,8 @@ skip_ed:
* have modified this list. normally it's just prepending
* entries (which we'd ignore), but paranoia won't hurt.
*/
+ *last = ed->ed_next;
+ ed->ed_next = NULL;
modified = 0;
/* unlink urbs as requested, but rescan the list after
@@ -1076,21 +1078,22 @@ rescan_this:
goto rescan_this;
/*
- * If no TDs are queued, take ED off the ed_rm_list.
+ * If no TDs are queued, ED is now idle.
* Otherwise, if the HC is running, reschedule.
- * If not, leave it on the list for further dequeues.
+ * If the HC isn't running, add ED back to the
+ * start of the list for later processing.
*/
if (list_empty(&ed->td_list)) {
- *last = ed->ed_next;
- ed->ed_next = NULL;
ed->state = ED_IDLE;
list_del(&ed->in_use_list);
} else if (ohci->rh_state == OHCI_RH_RUNNING) {
- *last = ed->ed_next;
- ed->ed_next = NULL;
ed_schedule(ohci, ed);
} else {
- last = &ed->ed_next;
+ ed->ed_next = ohci->ed_rm_list;
+ ohci->ed_rm_list = ed;
+ /* Don't loop on the same ED */
+ if (last == &ohci->ed_rm_list)
+ last = &ed->ed_next;
}
if (modified)
Patches currently in stable-queue which might be from aman.deep@xxxxxxxxxxx are
queue-4.4/usb-ohci-proper-handling-of-ed_rm_list-to-handle-race-condition-between-usb_kill_urb-and-finish_unlinks.patch