diff options
| author | AMAN DEEP <aman.deep@samsung.com> | 2018-02-08 06:55:01 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-02-15 20:45:34 +0300 |
| commit | 46408ea558df13b110e0866b99624384a33bdeba (patch) | |
| tree | 0022901a5c3a6c9f35e8179ad1be00b313f2ec24 /drivers/usb | |
| parent | 91b119359c1c3033a6621909d3c5dbbdf201d6b4 (diff) | |
| download | linux-46408ea558df13b110e0866b99624384a33bdeba.tar.xz | |
usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb')
| -rw-r--r-- | drivers/usb/host/ohci-q.c | 17 |
1 files 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 @@ 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 @@ -1077,21 +1079,22 @@ 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) |