| Message ID | 1438236923-17889-1-git-send-email-nab@daterainc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jul 30, 2015 at 06:15:23AM +0000, Nicholas A. Bellinger wrote: > From: Nicholas Bellinger <nab@linux-iscsi.org> > > This patch addresses a v4.2-rc1 regression where backend driver > struct module unload immediately after ->free_device() has done > an internal call_rcu(), results in IRQ rcu_process_callbacks() > use-after-free paging OOPsen. > > It adds a explicit synchronize_rcu() in target_backend_unregister() > to wait a full RCU grace period before releasing target_backend_ops > memory, and allowing TBO->module exit to proceed. Good catch, but... You need rcu_barrier() rather than synchronize_rcu() in this case. All that synchronize_rcu() does is wait for pre-existing RCU readers, when what is needed is to wait for all pre-existing RCU callbacks to be invoked. So please replace the two synchronize_rcu() calls with rcu_barrier(). Thanx, Paul > Also, go ahead and do the same for target_unregister_template() > to ensure se_deve_entry->rcu_head -> kfree_rcu() grace period has > passed, before allowing target_core_fabric_ops->owner module exit > to proceed. > > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Christoph Hellwig <hch@lst.de> > Cc: Hannes Reinecke <hare@suse.de> > Cc: Sagi Grimberg <sagig@mellanox.com> > Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org> > --- > drivers/target/target_core_configfs.c | 10 +++++++++- > drivers/target/target_core_hba.c | 10 +++++++++- > 2 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c > index c2e9fea..b4c3ae0 100644 > --- a/drivers/target/target_core_configfs.c > +++ b/drivers/target/target_core_configfs.c > @@ -457,8 +457,16 @@ void target_unregister_template(const struct target_core_fabric_ops *fo) > if (!strcmp(t->tf_ops->name, fo->name)) { > BUG_ON(atomic_read(&t->tf_access_cnt)); > list_del(&t->tf_list); > + mutex_unlock(&g_tf_lock); > + /* > + * Allow any outstanding fabric se_deve_entry->rcu_head > + * grace periods to expire post kfree_rcu(), before allowing > + * fabric driver unload of target_core_fabric_ops->module > + * to proceed. > + */ > + synchronize_rcu(); > kfree(t); > - break; > + return; > } > } > mutex_unlock(&g_tf_lock); > diff --git a/drivers/target/target_core_hba.c b/drivers/target/target_core_hba.c > index 62ea4e8..0fb830b 100644 > --- a/drivers/target/target_core_hba.c > +++ b/drivers/target/target_core_hba.c > @@ -84,8 +84,16 @@ void target_backend_unregister(const struct target_backend_ops *ops) > list_for_each_entry(tb, &backend_list, list) { > if (tb->ops == ops) { > list_del(&tb->list); > + mutex_unlock(&backend_mutex); > + /* > + * Allow any outstanding backend driver ->rcu_head grace > + * period to expire post ->free_device() -> call_rcu(), > + * before allowing backend driver module unload of > + * target_backend_ops->owner to proceed. > + */ > + synchronize_rcu(); > kfree(tb); > - break; > + return; > } > } > mutex_unlock(&backend_mutex); > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c index c2e9fea..b4c3ae0 100644 --- a/drivers/target/target_core_configfs.c +++ b/drivers/target/target_core_configfs.c @@ -457,8 +457,16 @@ void target_unregister_template(const struct target_core_fabric_ops *fo) if (!strcmp(t->tf_ops->name, fo->name)) { BUG_ON(atomic_read(&t->tf_access_cnt)); list_del(&t->tf_list); + mutex_unlock(&g_tf_lock); + /* + * Allow any outstanding fabric se_deve_entry->rcu_head + * grace periods to expire post kfree_rcu(), before allowing + * fabric driver unload of target_core_fabric_ops->module + * to proceed. + */ + synchronize_rcu(); kfree(t); - break; + return; } } mutex_unlock(&g_tf_lock); diff --git a/drivers/target/target_core_hba.c b/drivers/target/target_core_hba.c index 62ea4e8..0fb830b 100644 --- a/drivers/target/target_core_hba.c +++ b/drivers/target/target_core_hba.c @@ -84,8 +84,16 @@ void target_backend_unregister(const struct target_backend_ops *ops) list_for_each_entry(tb, &backend_list, list) { if (tb->ops == ops) { list_del(&tb->list); + mutex_unlock(&backend_mutex); + /* + * Allow any outstanding backend driver ->rcu_head grace + * period to expire post ->free_device() -> call_rcu(), + * before allowing backend driver module unload of + * target_backend_ops->owner to proceed. + */ + synchronize_rcu(); kfree(tb); - break; + return; } } mutex_unlock(&backend_mutex);