[ldv-project] [PATCH] usb: host: oxu210hp-hcd: Fix deadlock in oxu_qh_alloc()

[Alexey Khoroshilov]

oxu_qh_alloc() acquires oxu->mem_lock spinlock, finds free qh slot
and calls ehci_qtd_alloc() to initialize qh->dummy, but
ehci_qtd_alloc() acquires oxu->mem_lock as well.
That means an unavoidable deadlock in oxu_qh_alloc().

The patch fixes the issue by introduction of unlocked version
of ehci_qtd_alloc().

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov at ispras.ru>
---
 drivers/usb/host/oxu210hp-hcd.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/host/oxu210hp-hcd.c b/drivers/usb/host/oxu210hp-hcd.c
index 036924e640f5..15d4cf2c35cd 100644
--- a/drivers/usb/host/oxu210hp-hcd.c
+++ b/drivers/usb/host/oxu210hp-hcd.c
@@ -573,13 +573,11 @@ static inline void oxu_qtd_free(struct oxu_hcd *oxu, struct ehci_qtd *qtd)
 	spin_unlock(&oxu->mem_lock);
 }
 
-static struct ehci_qtd *ehci_qtd_alloc(struct oxu_hcd *oxu)
+static struct ehci_qtd *ehci_qtd_alloc_unlocked(struct oxu_hcd *oxu)
 {
 	int i;
 	struct ehci_qtd *qtd = NULL;
 
-	spin_lock(&oxu->mem_lock);
-
 	for (i = 0; i < QTD_NUM; i++)
 		if (!oxu->qtd_used[i])
 			break;
@@ -598,6 +596,17 @@ static struct ehci_qtd *ehci_qtd_alloc(struct oxu_hcd *oxu)
 		oxu->qtd_used[i] = 1;
 	}
 
+	return qtd;
+}
+
+static struct ehci_qtd *ehci_qtd_alloc(struct oxu_hcd *oxu)
+{
+	struct ehci_qtd *qtd;
+
+	spin_lock(&oxu->mem_lock);
+
+	qtd = ehci_qtd_alloc_unlocked(oxu);
+
 	spin_unlock(&oxu->mem_lock);
 
 	return qtd;
@@ -651,7 +660,7 @@ static struct ehci_qh *oxu_qh_alloc(struct oxu_hcd *oxu)
 		INIT_LIST_HEAD(&qh->qtd_list);
 
 		/* dummy td enables safe urb queuing */
-		qh->dummy = ehci_qtd_alloc(oxu);
+		qh->dummy = ehci_qtd_alloc_unlocked(oxu);
 		if (qh->dummy == NULL) {
 			oxu_dbg(oxu, "no dummy td\n");
 			oxu->qh_used[i] = 0;
-- 
1.9.1