| 1 | commit b3e670443b7fb8a2d29831b62b44a039c283e351 |
| 2 | Author: Christian Lamparter <chunkeey@googlemail.com> |
| 3 | Date: Tue Aug 3 02:32:28 2010 +0200 |
| 4 | |
| 5 | USB: fix thread-unsafe anchor utiliy routines |
| 6 | |
| 7 | This patch fixes a race condition in two utility routines |
| 8 | related to the removal/unlinking of urbs from an anchor. |
| 9 | |
| 10 | If two threads are concurrently accessing the same anchor, |
| 11 | both could end up with the same urb - thinking they are |
| 12 | the exclusive owner. |
| 13 | |
| 14 | Alan Stern pointed out a related issue in |
| 15 | usb_unlink_anchored_urbs: |
| 16 | |
| 17 | "The URB isn't removed from the anchor until it completes |
| 18 | (as a by-product of completion, in fact), which might not |
| 19 | be for quite some time after the unlink call returns. |
| 20 | In the meantime, the subroutine will keep trying to unlink |
| 21 | it, over and over again." |
| 22 | |
| 23 | Cc: stable <stable@kernel.org> |
| 24 | Cc: Oliver Neukum <oneukum@suse.de> |
| 25 | Cc: Greg Kroah-Hartman <greg@kroah.com> |
| 26 | Acked-by: Alan Stern <stern@rowland.harvard.edu> |
| 27 | Signed-off-by: Christian Lamparter <chunkeey@googlemail.com> |
| 28 | Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| 29 | |
| 30 | --- a/drivers/usb/core/urb.c |
| 31 | +++ b/drivers/usb/core/urb.c |
| 32 | @@ -137,6 +137,16 @@ void usb_anchor_urb(struct urb *urb, str |
| 33 | } |
| 34 | EXPORT_SYMBOL_GPL(usb_anchor_urb); |
| 35 | |
| 36 | +/* Callers must hold anchor->lock */ |
| 37 | +static void __usb_unanchor_urb(struct urb *urb, struct usb_anchor *anchor) |
| 38 | +{ |
| 39 | + urb->anchor = NULL; |
| 40 | + list_del(&urb->anchor_list); |
| 41 | + usb_put_urb(urb); |
| 42 | + if (list_empty(&anchor->urb_list)) |
| 43 | + wake_up(&anchor->wait); |
| 44 | +} |
| 45 | + |
| 46 | /** |
| 47 | * usb_unanchor_urb - unanchors an URB |
| 48 | * @urb: pointer to the urb to anchor |
| 49 | @@ -156,17 +166,14 @@ void usb_unanchor_urb(struct urb *urb) |
| 50 | return; |
| 51 | |
| 52 | spin_lock_irqsave(&anchor->lock, flags); |
| 53 | - if (unlikely(anchor != urb->anchor)) { |
| 54 | - /* we've lost the race to another thread */ |
| 55 | - spin_unlock_irqrestore(&anchor->lock, flags); |
| 56 | - return; |
| 57 | - } |
| 58 | - urb->anchor = NULL; |
| 59 | - list_del(&urb->anchor_list); |
| 60 | + /* |
| 61 | + * At this point, we could be competing with another thread which |
| 62 | + * has the same intention. To protect the urb from being unanchored |
| 63 | + * twice, only the winner of the race gets the job. |
| 64 | + */ |
| 65 | + if (likely(anchor == urb->anchor)) |
| 66 | + __usb_unanchor_urb(urb, anchor); |
| 67 | spin_unlock_irqrestore(&anchor->lock, flags); |
| 68 | - usb_put_urb(urb); |
| 69 | - if (list_empty(&anchor->urb_list)) |
| 70 | - wake_up(&anchor->wait); |
| 71 | } |
| 72 | EXPORT_SYMBOL_GPL(usb_unanchor_urb); |
| 73 | |
| 74 | @@ -713,20 +720,11 @@ EXPORT_SYMBOL_GPL(usb_unpoison_anchored_ |
| 75 | void usb_unlink_anchored_urbs(struct usb_anchor *anchor) |
| 76 | { |
| 77 | struct urb *victim; |
| 78 | - unsigned long flags; |
| 79 | |
| 80 | - spin_lock_irqsave(&anchor->lock, flags); |
| 81 | - while (!list_empty(&anchor->urb_list)) { |
| 82 | - victim = list_entry(anchor->urb_list.prev, struct urb, |
| 83 | - anchor_list); |
| 84 | - usb_get_urb(victim); |
| 85 | - spin_unlock_irqrestore(&anchor->lock, flags); |
| 86 | - /* this will unanchor the URB */ |
| 87 | + while ((victim = usb_get_from_anchor(anchor)) != NULL) { |
| 88 | usb_unlink_urb(victim); |
| 89 | usb_put_urb(victim); |
| 90 | - spin_lock_irqsave(&anchor->lock, flags); |
| 91 | } |
| 92 | - spin_unlock_irqrestore(&anchor->lock, flags); |
| 93 | } |
| 94 | EXPORT_SYMBOL_GPL(usb_unlink_anchored_urbs); |
| 95 | |
| 96 | @@ -763,12 +761,11 @@ struct urb *usb_get_from_anchor(struct u |
| 97 | victim = list_entry(anchor->urb_list.next, struct urb, |
| 98 | anchor_list); |
| 99 | usb_get_urb(victim); |
| 100 | - spin_unlock_irqrestore(&anchor->lock, flags); |
| 101 | - usb_unanchor_urb(victim); |
| 102 | + __usb_unanchor_urb(victim, anchor); |
| 103 | } else { |
| 104 | - spin_unlock_irqrestore(&anchor->lock, flags); |
| 105 | victim = NULL; |
| 106 | } |
| 107 | + spin_unlock_irqrestore(&anchor->lock, flags); |
| 108 | |
| 109 | return victim; |
| 110 | } |
| 111 | @@ -790,12 +787,7 @@ void usb_scuttle_anchored_urbs(struct us |
| 112 | while (!list_empty(&anchor->urb_list)) { |
| 113 | victim = list_entry(anchor->urb_list.prev, struct urb, |
| 114 | anchor_list); |
| 115 | - usb_get_urb(victim); |
| 116 | - spin_unlock_irqrestore(&anchor->lock, flags); |
| 117 | - /* this may free the URB */ |
| 118 | - usb_unanchor_urb(victim); |
| 119 | - usb_put_urb(victim); |
| 120 | - spin_lock_irqsave(&anchor->lock, flags); |
| 121 | + __usb_unanchor_urb(victim, anchor); |
| 122 | } |
| 123 | spin_unlock_irqrestore(&anchor->lock, flags); |
| 124 | } |
| 125 | |
