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authorAlan Stern <stern@rowland.harvard.edu>2010-11-16 10:57:37 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2010-12-09 13:24:18 -0800
commitacfaf795b87fa4f34022a2c127930848a93742d3 (patch)
treecb4ed5090d35332491ba24b52aeebf1ab9137ecd
parent3ddf4f97bee674e72412d9b0a3be2695d80dad3a (diff)
downloadlwn-acfaf795b87fa4f34022a2c127930848a93742d3.tar.gz
lwn-acfaf795b87fa4f34022a2c127930848a93742d3.zip
USB: EHCI: fix obscure race in ehci_endpoint_disable
commit 02e2c51ba3e80acde600721ea784c3ef84da5ea1 upstream. This patch (as1435) fixes an obscure and unlikely race in ehci-hcd. When an async URB is unlinked, the corresponding QH is removed from the async list. If the QH's endpoint is then disabled while the URB is being given back, ehci_endpoint_disable() won't find the QH on the async list, causing it to believe that the QH has been lost. This will lead to a memory leak at best and quite possibly to an oops. The solution is to trust usbcore not to lose track of endpoints. If the QH isn't on the async list then it doesn't need to be taken off the list, but the driver should still wait for the QH to become IDLE before disabling it. In theory this fixes Bugzilla #20182. In fact the race is so rare that it's not possible to tell whether the bug is still present. However, adding delays and making other changes to force the race seems to show that the patch works. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de> CC: David Brownell <david-b@pacbell.net> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--drivers/usb/host/ehci-hcd.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 6ef2a8928186..b1690ba14c18 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -954,10 +954,11 @@ rescan:
tmp && tmp != qh;
tmp = tmp->qh_next.qh)
continue;
- /* periodic qh self-unlinks on empty */
- if (!tmp)
- goto nogood;
- unlink_async (ehci, qh);
+ /* periodic qh self-unlinks on empty, and a COMPLETING qh
+ * may already be unlinked.
+ */
+ if (tmp)
+ unlink_async(ehci, qh);
/* FALL THROUGH */
case QH_STATE_UNLINK: /* wait for hw to finish? */
case QH_STATE_UNLINK_WAIT:
@@ -972,7 +973,6 @@ idle_timeout:
}
/* else FALL THROUGH */
default:
-nogood:
/* caller was supposed to have unlinked any requests;
* that's not our job. just leak this memory.
*/