From: AMAN DEEP aman.deep@samsung.com
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@rowland.harvard.edu CC: stable@vger.kernel.org Signed-off-by: Aman Deep aman.deep@samsung.com Signed-off-by: Jeffy Chen jeffy.chen@rock-chips.com ---
Changes in v6: This is a resend of Aman Deep's v5 patch [0], which solved the hang we hit [1]. (Thanks Aman :)
The v5 has some format issues, so i slightly adjust the commit message.
[0] https://www.spinics.net/lists/linux-usb/msg129010.html [1] https://bugs.chromium.org/p/chromium/issues/detail?id=803749
drivers/usb/host/ohci-q.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/drivers/usb/host/ohci-q.c b/drivers/usb/host/ohci-q.c index b2ec8c399363..4ccb85a67bb3 100644 --- a/drivers/usb/host/ohci-q.c +++ b/drivers/usb/host/ohci-q.c @@ -1019,6 +1019,8 @@ static void finish_unlinks(struct ohci_hcd *ohci) * 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 @@ -1077,21 +1079,22 @@ static void finish_unlinks(struct ohci_hcd *ohci) 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)