| Message ID | 1438302223.32325.7.camel@haakon3.risingtidesystems.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jul 30, 2015 at 05:23:43PM -0700, Nicholas A. Bellinger wrote: > On Thu, 2015-07-30 at 06:07 -0700, Paul E. McKenney wrote: > > 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. > > > > Ah, was getting confused by rcu_barrier_tasks() being specific to > CONFIG_TASKS_RCU in update.c code, and missing rcu_barrier() in > tree_plugin.h. > > Should have taken a look at Documentation/RCU/rcubarrier.txt.. > > > So please replace the two synchronize_rcu() calls with rcu_barrier(). > > > > <nod>, below is the updated version. > > Thanks for the review! Much better! Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --nab > > >From 9721910116f9883c7afded613ec88dc2de12339a Mon Sep 17 00:00:00 2001 > From: Nicholas Bellinger <nab@linux-iscsi.org> > Date: Wed, 29 Jul 2015 22:27:13 -0700 > Subject: [PATCH] target: Perform RCU callback barrier before backend/fabric > unload > > This patch addresses a v4.2-rc1 regression where backend driver > module unload happening immediately after TBO->free_device() > does internal call_rcu(), will currently result in IRQ context > rcu_process_callbacks() use-after-free paging OOPsen. > > It adds the missing rcu_barrier() in target_backend_unregister() > to perform an explicit RCU barrier waiting for all RCU callbacks > to complete before releasing target_backend_ops memory, and > allowing TBO->module exit to proceed. > > Also, do the same for fabric drivers in target_unregister_template() > to ensure se_deve_entry->rcu_head -> kfree_rcu() callbacks have > completed, 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 | 9 ++++++++- > drivers/target/target_core_hba.c | 10 +++++++++- > 2 files changed, 17 insertions(+), 2 deletions(-) > > diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c > index c2e9fea..860e840 100644 > --- a/drivers/target/target_core_configfs.c > +++ b/drivers/target/target_core_configfs.c > @@ -457,8 +457,15 @@ 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); > + /* > + * Wait for any outstanding fabric se_deve_entry->rcu_head > + * callbacks to complete post kfree_rcu(), before allowing > + * fabric driver unload of TFO->module to proceed. > + */ > + rcu_barrier(); > 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..be9cefc 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); > + /* > + * Wait for any outstanding backend driver ->rcu_head > + * callbacks to complete post TBO->free_device() -> > + * call_rcu(), before allowing backend driver module > + * unload of target_backend_ops->owner to proceed. > + */ > + rcu_barrier(); > 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..860e840 100644 --- a/drivers/target/target_core_configfs.c +++ b/drivers/target/target_core_configfs.c @@ -457,8 +457,15 @@ 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); + /* + * Wait for any outstanding fabric se_deve_entry->rcu_head + * callbacks to complete post kfree_rcu(), before allowing + * fabric driver unload of TFO->module to proceed. + */ + rcu_barrier(); 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..be9cefc 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); + /* + * Wait for any outstanding backend driver ->rcu_head + * callbacks to complete post TBO->free_device() -> + * call_rcu(), before allowing backend driver module + * unload of target_backend_ops->owner to proceed. + */ + rcu_barrier(); kfree(tb); - break; + return; } } mutex_unlock(&backend_mutex);