No need, since end_unlink_async() only got called when reclaim is not
NULL, please check the file ehci-hcd.c.
regards,
Yuping Luo
On Fri, Jan 22, 2010 at 5:16 PM, jidong xiao <jidong.xiao@xxxxxxxxx> wrote:
> Hi,
>
> I am reading the source code of drivers/usb/host/ehci-q.c, and
> following is the source code of function end_unlink_async().
>
> My question is, is there a potential NULL pointer dereference issue in
> this function, I mean, in line 1136 we get 'qh', but if this pointer
> is NULL, then when we run line 1142 and the lines after that, we may
> encounter NULL pointer dereference issue. I guess we have to ensure
> if(qh!=NULL) it true before we do any operation with its member.
>
> Regards
> Jason
>
> 1132 /* the async qh for the qtds being reclaimed are now unlinked
> from the HC */
> 1133
> 1134 static void end_unlink_async (struct ehci_hcd *ehci)
> 1135 {
> 1136 struct ehci_qh *qh = ehci->reclaim;
> 1137 struct ehci_qh *next;
> 1138
> 1139 iaa_watchdog_done(ehci);
> 1140
> 1141 // qh->hw_next = cpu_to_hc32(qh->qh_dma);
> 1142 qh->qh_state = QH_STATE_IDLE;
> 1143 qh->qh_next.qh = NULL;
> 1144 qh_put (qh); // refcount from reclaim
> 1145
> 1146 /* other unlink(s) may be pending (in QH_STATE_UNLINK_WAIT) */
> 1147 next = qh->reclaim;
> 1148 ehci->reclaim = next;
> 1149 qh->reclaim = NULL;
> 1150
> 1151 qh_completions (ehci, qh);
> 1152
> 1153 if (!list_empty (&qh->qtd_list)
> 1154 && HC_IS_RUNNING (ehci_to_hcd(ehci)->state))
> 1155 qh_link_async (ehci, qh);
> 1156 else {
> 1157 /* it's not free to turn the async schedule
> on/off; leave it
> 1158 * active but idle for a while once it empties.
> 1159 */
> 1160 if (HC_IS_RUNNING (ehci_to_hcd(ehci)->state)
> 1161 && ehci->async->qh_next.qh == NULL)
> 1162 timer_action (ehci, TIMER_ASYNC_OFF);
> 1163 }
> 1164 qh_put(qh); /* refcount from async list */
> 1165
> 1166 if (next) {
> 1167 ehci->reclaim = NULL;
> 1168 start_unlink_async (ehci, next);
> 1169 }
> 1170 }
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