Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=a460ef8d0a98ac9ef6b829ae292c9b6c13bc0120
Commit: a460ef8d0a98ac9ef6b829ae292c9b6c13bc0120
Parent: 1cf24bdbbbd2eb5439796dc399ab1649d150ed1d
Author: Dean Nelson <[EMAIL PROTECTED]>
AuthorDate: Wed Nov 22 08:25:00 2006 -0600
Committer: Tony Luck <[EMAIL PROTECTED]>
CommitDate: Tue Dec 12 11:48:53 2006 -0800
[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 <[EMAIL PROTECTED]>
Signed-off-by: Tony Luck <[EMAIL PROTECTED]>
---
arch/ia64/sn/kernel/xpc_channel.c | 15 ++++++---
arch/ia64/sn/kernel/xpc_main.c | 64 +++++++++++++++++++++++++------------
include/asm-ia64/sn/xpc.h | 2 +-
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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