[v5,2/2] nfs: protect callback execution against per-net callback thread shutdown

Submitted by Stanislav Kinsburskiy on Nov. 8, 2017, 5:23 p.m.

Details

Message ID 20171108172340.32634.90342.stgit@localhost.localdomain
State New
Series "nfs: fix race between callback shutdown and execution"
Headers show

Commit Message

Stanislav Kinsburskiy Nov. 8, 2017, 5:23 p.m.
From: Stanislav Kinsburskiy <skinsbursky@parallels.com>

Here is the race:

CPU #0				CPU#1

cleanup_mnt			nfs41_callback_svc (get xprt from the list)
nfs_callback_down		...
...				...
svc_close_net			...
...				...
svc_xprt_free			...
svc_bc_sock_free		bc_svc_process
kfree(xprt)			svc_process_common
				rqstp->rq_xprt->xpt_ops (use after free)

The problem is that per-net SUNRPC transports shutdown is done regardless
current callback execution. This is a race leading to transport use-after-free
in callback handler.
This patch fixes it in stright-forward way. I.e. it protects callback
execution with the same mutex used for per-net data creation and destruction.
Hopefully, it won't slow down NFS client significantly.

https://jira.sw.ru/browse/PSBM-75751

v5: destroy all per-net backchannel requests before transports on in
nfs_callback_down_net

v4: use another mutex to protect callback execution agains per-net transports
shutdown.
This guarantees, that transports won't be destroyed by shutdown callback while
execution is in progress and vice versa.

v3: Fix mutex deadlock, when shutdown callback waits for thread to exit (with
mutex taken), while thread wait for the mutex to take.
The idea is to simply check if thread has to exit, if mutex lock has failed.
This is a busy loop, but it shouldn't happend often and for long.

Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
---
 fs/nfs/callback.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Patch hide | download patch | download mbox

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 0beb275..e18d774 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -99,6 +99,8 @@  nfs4_callback_up(struct svc_serv *serv)
 }
 
 #if defined(CONFIG_NFS_V4_1)
+static DEFINE_MUTEX(nfs41_callback_mutex);
+
 /*
  * The callback service for NFSv4.1 callbacks
  */
@@ -117,6 +119,12 @@  nfs41_callback_svc(void *vrqstp)
 		if (try_to_freeze())
 			continue;
 
+		mutex_lock(&nfs41_callback_mutex);
+		if (kthread_should_stop()) {
+			mutex_unlock(&nfs41_callback_mutex);
+			return 0;
+		}
+
 		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
 		spin_lock_bh(&serv->sv_cb_lock);
 		if (!list_empty(&serv->sv_cb_list)) {
@@ -129,8 +137,10 @@  nfs41_callback_svc(void *vrqstp)
 			error = bc_svc_process(serv, req, rqstp);
 			dprintk("bc_svc_process() returned w/ error code= %d\n",
 				error);
+			mutex_unlock(&nfs41_callback_mutex);
 		} else {
 			spin_unlock_bh(&serv->sv_cb_lock);
+			mutex_unlock(&nfs41_callback_mutex);
 			schedule();
 			finish_wait(&serv->sv_cb_waitq, &wq);
 		}
@@ -242,6 +252,7 @@  static void nfs_callback_down_net(u32 minorversion, struct svc_serv *serv, struc
 		return;
 
 	dprintk("NFS: destroy per-net callback data; net=%p\n", net);
+	bc_svc_flush_queue_net(serv, net);
 	svc_shutdown_net(serv, net);
 }
 
@@ -377,7 +388,13 @@  void nfs_callback_down(int minorversion, struct net *net)
 	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
 
 	mutex_lock(&nfs_callback_mutex);
+#if defined(CONFIG_NFS_V4_1)
+	mutex_lock(&nfs41_callback_mutex);
+	nfs_callback_down_net(minorversion, cb_info->serv, net);
+	mutex_unlock(&nfs41_callback_mutex);
+#else
 	nfs_callback_down_net(minorversion, cb_info->serv, net);
+#endif
 	cb_info->users--;
 	if (cb_info->users == 0 && cb_info->task != NULL) {
 		kthread_stop(cb_info->task);

Comments

Kirill Tkhai Nov. 9, 2017, 9:33 a.m.
On 08.11.2017 20:23, Stanislav Kinsburskiy wrote:
> From: Stanislav Kinsburskiy <skinsbursky@parallels.com>
> 
> Here is the race:
> 
> CPU #0				CPU#1
> 
> cleanup_mnt			nfs41_callback_svc (get xprt from the list)
> nfs_callback_down		...
> ...				...
> svc_close_net			...
> ...				...
> svc_xprt_free			...
> svc_bc_sock_free		bc_svc_process
> kfree(xprt)			svc_process_common
> 				rqstp->rq_xprt->xpt_ops (use after free)
> 
> The problem is that per-net SUNRPC transports shutdown is done regardless
> current callback execution. This is a race leading to transport use-after-free
> in callback handler.
> This patch fixes it in stright-forward way. I.e. it protects callback
> execution with the same mutex used for per-net data creation and destruction.
> Hopefully, it won't slow down NFS client significantly.
> 
> https://jira.sw.ru/browse/PSBM-75751
> 
> v5: destroy all per-net backchannel requests before transports on in
> nfs_callback_down_net
> 
> v4: use another mutex to protect callback execution agains per-net transports
> shutdown.
> This guarantees, that transports won't be destroyed by shutdown callback while
> execution is in progress and vice versa.
> 
> v3: Fix mutex deadlock, when shutdown callback waits for thread to exit (with
> mutex taken), while thread wait for the mutex to take.
> The idea is to simply check if thread has to exit, if mutex lock has failed.
> This is a busy loop, but it shouldn't happend often and for long.
> 
> Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
> ---
>  fs/nfs/callback.c |   17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
> index 0beb275..e18d774 100644
> --- a/fs/nfs/callback.c
> +++ b/fs/nfs/callback.c
> @@ -99,6 +99,8 @@ nfs4_callback_up(struct svc_serv *serv)
>  }
>  
>  #if defined(CONFIG_NFS_V4_1)
> +static DEFINE_MUTEX(nfs41_callback_mutex);
> +
>  /*
>   * The callback service for NFSv4.1 callbacks
>   */
> @@ -117,6 +119,12 @@ nfs41_callback_svc(void *vrqstp)
>  		if (try_to_freeze())
>  			continue;
>  
> +		mutex_lock(&nfs41_callback_mutex);
> +		if (kthread_should_stop()) {
> +			mutex_unlock(&nfs41_callback_mutex);
> +			return 0;
> +		}
> +
>  		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
>  		spin_lock_bh(&serv->sv_cb_lock);
>  		if (!list_empty(&serv->sv_cb_list)) {
> @@ -129,8 +137,10 @@ nfs41_callback_svc(void *vrqstp)
>  			error = bc_svc_process(serv, req, rqstp);
>  			dprintk("bc_svc_process() returned w/ error code= %d\n",
>  				error);
> +			mutex_unlock(&nfs41_callback_mutex);
>  		} else {
>  			spin_unlock_bh(&serv->sv_cb_lock);
> +			mutex_unlock(&nfs41_callback_mutex);
>  			schedule();
>  			finish_wait(&serv->sv_cb_waitq, &wq);
>  		}
> @@ -242,6 +252,7 @@ static void nfs_callback_down_net(u32 minorversion, struct svc_serv *serv, struc
>  		return;
>  
>  	dprintk("NFS: destroy per-net callback data; net=%p\n", net);
> +	bc_svc_flush_queue_net(serv, net);
>  	svc_shutdown_net(serv, net);
>  }
>  
> @@ -377,7 +388,13 @@ void nfs_callback_down(int minorversion, struct net *net)
>  	struct nfs_callback_data *cb_info = &nfs_callback_info[minorversion];
>  
>  	mutex_lock(&nfs_callback_mutex);
> +#if defined(CONFIG_NFS_V4_1)
> +	mutex_lock(&nfs41_callback_mutex);
> +	nfs_callback_down_net(minorversion, cb_info->serv, net);
> +	mutex_unlock(&nfs41_callback_mutex);
> +#else
>  	nfs_callback_down_net(minorversion, cb_info->serv, net);
> +#endif
>  	cb_info->users--;
>  	if (cb_info->users == 0 && cb_info->task != NULL) {
>  		kthread_stop(cb_info->task);
> 

Looks good for me, except there is one more call of nfs_callback_down_net() in nfs_callback_up().
It's not clear for me, we shouldn't protect it via the mutex too. Should we?
Stanislav Kinsburskiy Nov. 9, 2017, 9:46 a.m.
09.11.2017 10:33, Kirill Tkhai пишет:
> 
> Looks good for me, except there is one more call of nfs_callback_down_net() in nfs_callback_up().
> It's not clear for me, we shouldn't protect it via the mutex too. Should we?
> 

Looks like no, mount is not ready yet and there is no connection to server, thus no request from server can
come to the moment and we don't need any additional protection here.