Messages in this thread Patch in this message | | | Date | Thu, 28 Dec 2006 12:24:47 -0600 | From | Corey Minyard <> | Subject | [PATCH] IPMI: fix some RCU problems |
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Fix some RCU problem pointed out by Paul McKenney of IBM. These are:
The wholesale move of the command receivers list into a new list was not safe because the list will point to the new tail during a traversal, so the traversal will never end on a reader if this happens during a read.
Memory barriers were needed to handle proper ordering of the setting of the IPMI interface as valid. Readers might not see proper ordering of data otherwise.
In ipmi_smi_watcher_register(), the use of the _rcu suffix on the list is unnecessary.
Signed-off-by: Corey Minyard <minyard@acm.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Index: linux-2.6.19/drivers/char/ipmi/ipmi_msghandler.c =================================================================== --- linux-2.6.19.orig/drivers/char/ipmi/ipmi_msghandler.c +++ linux-2.6.19/drivers/char/ipmi/ipmi_msghandler.c @@ -406,13 +406,31 @@ static void clean_up_interface_data(ipmi free_smi_msg_list(&intf->waiting_msgs); free_recv_msg_list(&intf->waiting_events); - /* Wholesale remove all the entries from the list in the - * interface and wait for RCU to know that none are in use. */ + /* + * Wholesale remove all the entries from the list in the + * interface and wait for RCU to know that none are in use. + */ mutex_lock(&intf->cmd_rcvrs_mutex); - list_add_rcu(&list, &intf->cmd_rcvrs); - list_del_rcu(&intf->cmd_rcvrs); + if (list_empty(&intf->cmd_rcvrs)) + INIT_LIST_HEAD(&list); + else { + list.next = intf->cmd_rcvrs.next; + list.prev = intf->cmd_rcvrs.prev; + INIT_LIST_HEAD(&intf->cmd_rcvrs); + + /* + * At this point the list body still points to + * intf->cmd_rcvrs. Wait for any readers to finish + * using the list before we switch the list body over + * to the new list. + */ + synchronize_rcu(); + + /* Ready the list for use. */ + list.next->prev = &list; + list.prev->next = &list; + } mutex_unlock(&intf->cmd_rcvrs_mutex); - synchronize_rcu(); list_for_each_entry_safe(rcvr, rcvr2, &list, link) kfree(rcvr); @@ -451,7 +469,7 @@ int ipmi_smi_watcher_register(struct ipm mutex_lock(&ipmi_interfaces_mutex); /* Build a list of things to deliver. */ - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { + list_for_each_entry(intf, &ipmi_interfaces, link) { if (intf->intf_num == -1) continue; e = kmalloc(sizeof(*e), GFP_KERNEL); @@ -838,6 +856,7 @@ int ipmi_create_user(unsigned int goto out_kfree; found: + smp_rmb(); /* Note that each existing user holds a refcount to the interface. */ kref_get(&intf->refcount); @@ -2761,6 +2780,7 @@ int ipmi_register_smi(struct ipmi_smi_ha kref_put(&intf->refcount, intf_free); } else { /* After this point the interface is legal to use. */ + smp_wmb(); /* Keep memory order straight for RCU readers. */ intf->intf_num = i; mutex_unlock(&ipmi_interfaces_mutex); call_smi_watchers(i, intf->si_dev); @@ -3924,6 +3944,8 @@ static void send_panic_events(char *str) /* Interface was not ready yet. */ continue; + smp_rmb(); + /* First job here is to figure out where to send the OEM events. There's no way in IPMI to send OEM events using an event send command, so we have to - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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