[PATCH v2 1/5] sunrpc: keep a count of swapfiles associated with the rpc_clnt

Jeff Layton
2015-06-03T14:44:11Z

Jerome reported seeing a warning pop when working with a swapfile on
NFS. The nfs_swap_activate can end up calling sk_set_memalloc while
holding the rcu_read_lock and that function can sleep.

To fix that, we need to take a reference to the xprt while holding the
rcu_read_lock, set the socket up for swapping and then drop that
reference. But, xprt_put is not exported and having NFS deal with the
underlying xprt is a bit of layering violation anyway.

Fix this by adding a set of activate/deactivate functions that take a
rpc_clnt pointer instead of an rpc_xprt, and have nfs_swap_activate and
nfs_swap_deactivate call those.

Also, add a per-rpc_clnt atomic counter to keep track of the number of
active swapfiles associated with it. When the counter does a 0->1
transition, we enable swapping on the xprt, when we do a 1->0 transition
we disable swapping on it.

This also allows us to be a bit more selective with the RPC_TASK_SWAPPER
flag. If non-swapper and swapper clnts are sharing a xprt, then we only
need to flag the tasks from the swapper clnt with that flag.

Acked-by: Mel Gorman <mgorman@suse.de>
Reported-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
---
fs/nfs/file.c | 11 ++------
include/linux/sunrpc/clnt.h | 1 +
include/linux/sunrpc/sched.h | 16 +++++++++++
net/sunrpc/clnt.c | 67 ++++++++++++++++++++++++++++++++++++++------
net/sunrpc/xprtsock.c | 1 -
5 files changed, 77 insertions(+), 19 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 8b8d83a526ce..7b26840ccfe1 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -559,25 +559,18 @@ static int nfs_launder_page(struct page *page)
static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
sector_t *span)
{
- int ret;
struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);

*span = sis->pages;

- rcu_read_lock();
- ret = xs_swapper(rcu_dereference(clnt->cl_xprt), 1);
- rcu_read_unlock();
-
- return ret;
+ return rpc_clnt_swap_activate(clnt);
}

static void nfs_swap_deactivate(struct file *file)
{
struct rpc_clnt *clnt = NFS_CLIENT(file->f_mapping->host);

- rcu_read_lock();
- xs_swapper(rcu_dereference(clnt->cl_xprt), 0);
- rcu_read_unlock();
+ rpc_clnt_swap_deactivate(clnt);
}
#endif

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index 598ba80ec30c..131032f15cc1 100644
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -56,6 +56,7 @@ struct rpc_clnt {
struct rpc_rtt * cl_rtt; /* RTO estimator data */
const struct rpc_timeout *cl_timeout; /* Timeout strategy */

+ atomic_t cl_swapper; /* swapfile count */
int cl_nodelen; /* nodename length */
char cl_nodename[UNX_MAXNODENAME+1];
struct rpc_pipe_dir_head cl_pipedir_objects;
diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
index 5f1e6bd4c316..50472d716e72 100644
--- a/include/linux/sunrpc/sched.h
+++ b/include/linux/sunrpc/sched.h
@@ -269,4 +269,20 @@ static inline void rpc_assign_waitqueue_name(struct rpc_wait_queue *q,
}
#endif

+#if IS_ENABLED(CONFIG_SUNRPC_SWAP)
+int rpc_clnt_swap_activate(struct rpc_clnt *clnt);
+void rpc_clnt_swap_deactivate(struct rpc_clnt *clnt);
+#else
+static inline int
+rpc_clnt_swap_activate(struct rpc_clnt *clnt)
+{
+ return 0;
+}
+
+static inline void
+rpc_clnt_swap_deactivate(struct rpc_clnt *clnt)
+{
+}
+#endif /* CONFIG_SUNRPC_SWAP */
+
#endif /* _LINUX_SUNRPC_SCHED_H_ */
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index e6ce1517367f..383cb778179f 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -891,15 +891,8 @@ void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
task->tk_flags |= RPC_TASK_SOFT;
if (clnt->cl_noretranstimeo)
task->tk_flags |= RPC_TASK_NO_RETRANS_TIMEOUT;
- if (sk_memalloc_socks()) {
- struct rpc_xprt *xprt;
-
- rcu_read_lock();
- xprt = rcu_dereference(clnt->cl_xprt);
- if (xprt->swapper)
- task->tk_flags |= RPC_TASK_SWAPPER;
- rcu_read_unlock();
- }
+ if (atomic_read(&clnt->cl_swapper))
+ task->tk_flags |= RPC_TASK_SWAPPER;
/* Add to the client's list of all tasks */
spin_lock(&clnt->cl_lock);
list_add_tail(&task->tk_task, &clnt->cl_tasks);
@@ -2476,3 +2469,59 @@ void rpc_show_tasks(struct net *net)
spin_unlock(&sn->rpc_client_lock);
}
#endif
+
+#if IS_ENABLED(CONFIG_SUNRPC_SWAP)
+int
+rpc_clnt_swap_activate(struct rpc_clnt *clnt)
+{
+ int ret = 0;
+ struct rpc_xprt *xprt;
+
+ if (atomic_inc_return(&clnt->cl_swapper) == 1) {
+retry:
+ rcu_read_lock();
+ xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
+ rcu_read_unlock();
+ if (!xprt) {
+ /*
+ * If we didn't get a reference, then we likely are
+ * racing with a migration event. Wait for a grace
+ * period and try again.
+ */
+ synchronize_rcu();
+ goto retry;
+ }
+
+ ret = xs_swapper(xprt, 1);
+ xprt_put(xprt);
+ }
+ return ret;
+}
+EXPORT_SYMBOL_GPL(rpc_clnt_swap_activate);
+
+void
+rpc_clnt_swap_deactivate(struct rpc_clnt *clnt)
+{
+ struct rpc_xprt *xprt;
+
+ if (atomic_dec_if_positive(&clnt->cl_swapper) == 0) {
+retry:
+ rcu_read_lock();
+ xprt = xprt_get(rcu_dereference(clnt->cl_xprt));
+ rcu_read_unlock();
+ if (!xprt) {
+ /*
+ * If we didn't get a reference, then we likely are
+ * racing with a migration event. Wait for a grace
+ * period and try again.
+ */
+ synchronize_rcu();
+ goto retry;
+ }
+
+ xs_swapper(xprt, 0);
+ xprt_put(xprt);
+ }
+}
+EXPORT_SYMBOL_GPL(rpc_clnt_swap_deactivate);
+#endif /* CONFIG_SUNRPC_SWAP */
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 66891e32c5e3..b29703996028 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -1992,7 +1992,6 @@ int xs_swapper(struct rpc_xprt *xprt, int enable)

return err;
}
-EXPORT_SYMBOL_GPL(xs_swapper);
#else
static void xs_set_memalloc(struct rpc_xprt *xprt)
{