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authorDean Nelson <dcn@sgi.com>2006-11-22 08:25:00 -0600
committerTony Luck <tony.luck@intel.com>2006-12-12 11:48:53 -0800
commita460ef8d0a98ac9ef6b829ae292c9b6c13bc0120 (patch)
treeda52a77a9fee80f98a8a82567814f33d2341234b
parent1cf24bdbbbd2eb5439796dc399ab1649d150ed1d (diff)
downloadop-kernel-dev-a460ef8d0a98ac9ef6b829ae292c9b6c13bc0120.zip
op-kernel-dev-a460ef8d0a98ac9ef6b829ae292c9b6c13bc0120.tar.gz
[IA64] fix possible XPC deadlock when disconnecting
This patch eliminates a potential deadlock that is possible when XPC disconnects a channel to a partition that has gone down. This deadlock will occur if at least one of the kthreads created by XPC for the purpose of making callouts to the channel's registerer is detained in the registerer and will not be returning back to XPC until some registerer request occurs on the now downed partition. The potential for a deadlock is removed by ensuring that there always is a kthread available to make the channel disconnecting callout to the registerer. Signed-off-by: Dean Nelson <dcn@sgi.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
-rw-r--r--arch/ia64/sn/kernel/xpc_channel.c15
-rw-r--r--arch/ia64/sn/kernel/xpc_main.c64
-rw-r--r--include/asm-ia64/sn/xpc.h2
3 files changed, 54 insertions, 27 deletions
diff --git a/arch/ia64/sn/kernel/xpc_channel.c b/arch/ia64/sn/kernel/xpc_channel.c
index 1f35408..c08db9c 100644
--- a/arch/ia64/sn/kernel/xpc_channel.c
+++ b/arch/ia64/sn/kernel/xpc_channel.c
@@ -632,7 +632,7 @@ xpc_process_connect(struct xpc_channel *ch, unsigned long *irq_flags)
ch->number, ch->partid);
spin_unlock_irqrestore(&ch->lock, *irq_flags);
- xpc_create_kthreads(ch, 1);
+ xpc_create_kthreads(ch, 1, 0);
spin_lock_irqsave(&ch->lock, *irq_flags);
}
@@ -754,12 +754,12 @@ xpc_process_disconnect(struct xpc_channel *ch, unsigned long *irq_flags)
/* make sure all activity has settled down first */
- if (atomic_read(&ch->references) > 0 ||
- ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
- !(ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE))) {
+ if (atomic_read(&ch->kthreads_assigned) > 0 ||
+ atomic_read(&ch->references) > 0) {
return;
}
- DBUG_ON(atomic_read(&ch->kthreads_assigned) != 0);
+ DBUG_ON((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+ !(ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE));
if (part->act_state == XPC_P_DEACTIVATING) {
/* can't proceed until the other side disengages from us */
@@ -1651,6 +1651,11 @@ xpc_disconnect_channel(const int line, struct xpc_channel *ch,
/* wake all idle kthreads so they can exit */
if (atomic_read(&ch->kthreads_idle) > 0) {
wake_up_all(&ch->idle_wq);
+
+ } else if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+ !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
+ /* start a kthread that will do the xpcDisconnecting callout */
+ xpc_create_kthreads(ch, 1, 1);
}
/* wake those waiting to allocate an entry from the local msg queue */
diff --git a/arch/ia64/sn/kernel/xpc_main.c b/arch/ia64/sn/kernel/xpc_main.c
index fa96dfc..7a387d2 100644
--- a/arch/ia64/sn/kernel/xpc_main.c
+++ b/arch/ia64/sn/kernel/xpc_main.c
@@ -681,7 +681,7 @@ xpc_activate_kthreads(struct xpc_channel *ch, int needed)
dev_dbg(xpc_chan, "create %d new kthreads, partid=%d, channel=%d\n",
needed, ch->partid, ch->number);
- xpc_create_kthreads(ch, needed);
+ xpc_create_kthreads(ch, needed, 0);
}
@@ -775,26 +775,28 @@ xpc_daemonize_kthread(void *args)
xpc_kthread_waitmsgs(part, ch);
}
- if (atomic_dec_return(&ch->kthreads_assigned) == 0) {
- spin_lock_irqsave(&ch->lock, irq_flags);
- if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
- !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
- ch->flags |= XPC_C_DISCONNECTINGCALLOUT;
- spin_unlock_irqrestore(&ch->lock, irq_flags);
+ /* let registerer know that connection is disconnecting */
- xpc_disconnect_callout(ch, xpcDisconnecting);
-
- spin_lock_irqsave(&ch->lock, irq_flags);
- ch->flags |= XPC_C_DISCONNECTINGCALLOUT_MADE;
- }
+ spin_lock_irqsave(&ch->lock, irq_flags);
+ if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
+ !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
+ ch->flags |= XPC_C_DISCONNECTINGCALLOUT;
spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+ xpc_disconnect_callout(ch, xpcDisconnecting);
+
+ spin_lock_irqsave(&ch->lock, irq_flags);
+ ch->flags |= XPC_C_DISCONNECTINGCALLOUT_MADE;
+ }
+ spin_unlock_irqrestore(&ch->lock, irq_flags);
+
+ if (atomic_dec_return(&ch->kthreads_assigned) == 0) {
if (atomic_dec_return(&part->nchannels_engaged) == 0) {
xpc_mark_partition_disengaged(part);
xpc_IPI_send_disengage(part);
}
}
-
xpc_msgqueue_deref(ch);
dev_dbg(xpc_chan, "kthread exiting, partid=%d, channel=%d\n",
@@ -818,7 +820,8 @@ xpc_daemonize_kthread(void *args)
* partition.
*/
void
-xpc_create_kthreads(struct xpc_channel *ch, int needed)
+xpc_create_kthreads(struct xpc_channel *ch, int needed,
+ int ignore_disconnecting)
{
unsigned long irq_flags;
pid_t pid;
@@ -833,16 +836,38 @@ xpc_create_kthreads(struct xpc_channel *ch, int needed)
* kthread. That kthread is responsible for doing the
* counterpart to the following before it exits.
*/
+ if (ignore_disconnecting) {
+ if (!atomic_inc_not_zero(&ch->kthreads_assigned)) {
+ /* kthreads assigned had gone to zero */
+ BUG_ON(!(ch->flags &
+ XPC_C_DISCONNECTINGCALLOUT_MADE));
+ break;
+ }
+
+ } else if (ch->flags & XPC_C_DISCONNECTING) {
+ break;
+
+ } else if (atomic_inc_return(&ch->kthreads_assigned) == 1) {
+ if (atomic_inc_return(&part->nchannels_engaged) == 1)
+ xpc_mark_partition_engaged(part);
+ }
(void) xpc_part_ref(part);
xpc_msgqueue_ref(ch);
- if (atomic_inc_return(&ch->kthreads_assigned) == 1 &&
- atomic_inc_return(&part->nchannels_engaged) == 1) {
- xpc_mark_partition_engaged(part);
- }
pid = kernel_thread(xpc_daemonize_kthread, (void *) args, 0);
if (pid < 0) {
/* the fork failed */
+
+ /*
+ * NOTE: if (ignore_disconnecting &&
+ * !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) is true,
+ * then we'll deadlock if all other kthreads assigned
+ * to this channel are blocked in the channel's
+ * registerer, because the only thing that will unblock
+ * them is the xpcDisconnecting callout that this
+ * failed kernel_thread would have made.
+ */
+
if (atomic_dec_return(&ch->kthreads_assigned) == 0 &&
atomic_dec_return(&part->nchannels_engaged) == 0) {
xpc_mark_partition_disengaged(part);
@@ -857,9 +882,6 @@ xpc_create_kthreads(struct xpc_channel *ch, int needed)
* Flag this as an error only if we have an
* insufficient #of kthreads for the channel
* to function.
- *
- * No xpc_msgqueue_ref() is needed here since
- * the channel mgr is doing this.
*/
spin_lock_irqsave(&ch->lock, irq_flags);
XPC_DISCONNECT_CHANNEL(ch, xpcLackOfResources,
diff --git a/include/asm-ia64/sn/xpc.h b/include/asm-ia64/sn/xpc.h
index 1d45e15..e52b850 100644
--- a/include/asm-ia64/sn/xpc.h
+++ b/include/asm-ia64/sn/xpc.h
@@ -673,7 +673,7 @@ extern irqreturn_t xpc_notify_IRQ_handler(int, void *);
extern void xpc_dropped_IPI_check(struct xpc_partition *);
extern void xpc_activate_partition(struct xpc_partition *);
extern void xpc_activate_kthreads(struct xpc_channel *, int);
-extern void xpc_create_kthreads(struct xpc_channel *, int);
+extern void xpc_create_kthreads(struct xpc_channel *, int, int);
extern void xpc_disconnect_wait(int);
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