git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From 46408ea558df13b110e0866b99624384a33bdeba Mon Sep 17 00:00:00 2001
   2 From: AMAN DEEP <aman.deep@samsung.com>
   3 Date: Thu, 8 Feb 2018 11:55:01 +0800
   4 Subject: usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()
   5
   6 From: AMAN DEEP <aman.deep@samsung.com>
   7
   8 commit 46408ea558df13b110e0866b99624384a33bdeba upstream.
   9
  10 There is a race condition between finish_unlinks->finish_urb() function
  11 and usb_kill_urb() in ohci controller case. The finish_urb calls
  12 spin_unlock(&ohci->lock) before usb_hcd_giveback_urb() function call,
  13 then if during this time, usb_kill_urb is called for another endpoint,
  14 then new ed will be added to ed_rm_list at beginning for unlink, and
  15 ed_rm_list will point to newly added.
  16
  17 When finish_urb() is completed in finish_unlinks() and ed->td_list
  18 becomes empty as in below code (in finish_unlinks() function):
  19
  20         if (list_empty(&ed->td_list)) {
  21                 *last = ed->ed_next;
  22                 ed->ed_next = NULL;
  23         } else if (ohci->rh_state == OHCI_RH_RUNNING) {
  24                 *last = ed->ed_next;
  25                 ed->ed_next = NULL;
  26                 ed_schedule(ohci, ed);
  27         }
  28
  29 The *last = ed->ed_next will make ed_rm_list to point to ed->ed_next
  30 and previously added ed by usb_kill_urb will be left unreferenced by
  31 ed_rm_list. This causes usb_kill_urb() hang forever waiting for
  32 finish_unlink to remove added ed from ed_rm_list.
  33
  34 The main reason for hang in this race condtion is addition and removal
  35 of ed from ed_rm_list in the beginning during usb_kill_urb and later
  36 last* is modified in finish_unlinks().
  37
  38 As suggested by Alan Stern, the solution for proper handling of
  39 ohci->ed_rm_list is to remove ed from the ed_rm_list before finishing
  40 any URBs. Then at the end, we can add ed back to the list if necessary.
  41
  42 This properly handle the updated ohci->ed_rm_list in usb_kill_urb().
  43
  44 Fixes: 977dcfdc6031 ("USB: OHCI: don't lose track of EDs when a controller dies")
  45 Acked-by: Alan Stern <stern@rowland.harvard.edu>
  46 CC: <stable@vger.kernel.org>
  47 Signed-off-by: Aman Deep <aman.deep@samsung.com>
  48 Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
  49 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  50
  51 diff --git a/drivers/usb/host/ohci-q.c b/drivers/usb/host/ohci-q.c
  52 index b2ec8c399363..4ccb85a67bb3 100644
  53 --- a/drivers/usb/host/ohci-q.c
  54 +++ b/drivers/usb/host/ohci-q.c
  55 @@ -1019,6 +1019,8 @@ static void finish_unlinks(struct ohci_hcd *ohci)
  56                  * have modified this list.  normally it's just prepending
  57                  * entries (which we'd ignore), but paranoia won't hurt.
  58                  */
  59 +               *last = ed->ed_next;
  60 +               ed->ed_next = NULL;
  61                 modified = 0;
  62
  63                 /* unlink urbs as requested, but rescan the list after
  64 @@ -1077,21 +1079,22 @@ static void finish_unlinks(struct ohci_hcd *ohci)
  65                         goto rescan_this;
  66
  67                 /*
  68 -                * If no TDs are queued, take ED off the ed_rm_list.
  69 +                * If no TDs are queued, ED is now idle.
  70                  * Otherwise, if the HC is running, reschedule.
  71 -                * If not, leave it on the list for further dequeues.
  72 +                * If the HC isn't running, add ED back to the
  73 +                * start of the list for later processing.
  74                  */
  75                 if (list_empty(&ed->td_list)) {
  76 -                       *last = ed->ed_next;
  77 -                       ed->ed_next = NULL;
  78                         ed->state = ED_IDLE;
  79                         list_del(&ed->in_use_list);
  80                 } else if (ohci->rh_state == OHCI_RH_RUNNING) {
  81 -                       *last = ed->ed_next;
  82 -                       ed->ed_next = NULL;
  83                         ed_schedule(ohci, ed);
  84                 } else {
  85 -                       last = &ed->ed_next;
  86 +                       ed->ed_next = ohci->ed_rm_list;
  87 +                       ohci->ed_rm_list = ed;
  88 +                       /* Don't loop on the same ED */
  89 +                       if (last == &ohci->ed_rm_list)
  90 +                               last = &ed->ed_next;
  91                 }
  92
  93                 if (modified)