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Subject[PATCH 3.12 097/116] SUNRPC: Avoid deep recursion in rpc_release_client
Date
3.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <Trond.Myklebust@netapp.com>

commit d07ba8422f1e58be94cc98a1f475946dc1b89f1b upstream.

In cases where an rpc client has a parent hierarchy, then
rpc_free_client may end up calling rpc_release_client() on the
parent, thus recursing back into rpc_free_client. If the hierarchy
is deep enough, then we can get into situations where the stack
simply overflows.

The fix is to have rpc_release_client() loop so that it can take
care of the parent rpc client hierarchy without needing to
recurse.

Reported-by: Jeff Layton <jlayton@redhat.com>
Reported-by: Weston Andros Adamson <dros@netapp.com>
Reported-by: Bruce Fields <bfields@fieldses.org>
Link: http://lkml.kernel.org/r/2C73011F-0939-434C-9E4D-13A1EB1403D7@netapp.com
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/sunrpc/clnt.c | 29 +++++++++++++++++------------
1 file changed, 17 insertions(+), 12 deletions(-)

--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -656,14 +656,16 @@ EXPORT_SYMBOL_GPL(rpc_shutdown_client);
/*
* Free an RPC client
*/
-static void
+static struct rpc_clnt *
rpc_free_client(struct rpc_clnt *clnt)
{
+ struct rpc_clnt *parent = NULL;
+
dprintk_rcu("RPC: destroying %s client for %s\n",
clnt->cl_program->name,
rcu_dereference(clnt->cl_xprt)->servername);
if (clnt->cl_parent != clnt)
- rpc_release_client(clnt->cl_parent);
+ parent = clnt->cl_parent;
rpc_clnt_remove_pipedir(clnt);
rpc_unregister_client(clnt);
rpc_free_iostats(clnt->cl_metrics);
@@ -672,18 +674,17 @@ rpc_free_client(struct rpc_clnt *clnt)
rpciod_down();
rpc_free_clid(clnt);
kfree(clnt);
+ return parent;
}

/*
* Free an RPC client
*/
-static void
+static struct rpc_clnt *
rpc_free_auth(struct rpc_clnt *clnt)
{
- if (clnt->cl_auth == NULL) {
- rpc_free_client(clnt);
- return;
- }
+ if (clnt->cl_auth == NULL)
+ return rpc_free_client(clnt);

/*
* Note: RPCSEC_GSS may need to send NULL RPC calls in order to
@@ -694,7 +695,8 @@ rpc_free_auth(struct rpc_clnt *clnt)
rpcauth_release(clnt->cl_auth);
clnt->cl_auth = NULL;
if (atomic_dec_and_test(&clnt->cl_count))
- rpc_free_client(clnt);
+ return rpc_free_client(clnt);
+ return NULL;
}

/*
@@ -705,10 +707,13 @@ rpc_release_client(struct rpc_clnt *clnt
{
dprintk("RPC: rpc_release_client(%p)\n", clnt);

- if (list_empty(&clnt->cl_tasks))
- wake_up(&destroy_wait);
- if (atomic_dec_and_test(&clnt->cl_count))
- rpc_free_auth(clnt);
+ do {
+ if (list_empty(&clnt->cl_tasks))
+ wake_up(&destroy_wait);
+ if (!atomic_dec_and_test(&clnt->cl_count))
+ break;
+ clnt = rpc_free_auth(clnt);
+ } while (clnt != NULL);
}
EXPORT_SYMBOL_GPL(rpc_release_client);




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