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Subject[PATCH 4/4] nfs: deadlock prevention for NFS

Provide a proper a_ops->swapfile() implementation for NFS. This will
set the NFS socket to SOCK_VMIO and put the socket reconnection under
PF_MEMALLOC (I hope this is enough, otherwise more work needs to be done).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
fs/nfs/file.c | 21 ++++++++++++++++++++-
include/linux/sunrpc/xprt.h | 4 +++-
net/sunrpc/xprtsock.c | 16 ++++++++++++++++
3 files changed, 39 insertions(+), 2 deletions(-)

Index: linux-2.6/fs/nfs/file.c
===================================================================
--- linux-2.6.orig/fs/nfs/file.c
+++ linux-2.6/fs/nfs/file.c
@@ -27,6 +27,7 @@
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/smp_lock.h>
+#include <net/sock.h>

#include <asm/uaccess.h>
#include <asm/system.h>
@@ -317,7 +318,25 @@ static int nfs_release_page(struct page

static int nfs_swapfile(struct address_space *mapping, int enable)
{
- return 0;
+ int err = -EINVAL;
+ struct rpc_clnt *client = NFS_CLIENT(mapping->host);
+ struct sock *sk = client->cl_xprt->inet;
+
+ if (enable) {
+ client->cl_xprt->swapper = 1;
+ /*
+ * keep one extra sock reference so the reserve won't dip
+ * when the socket gets reconnected.
+ */
+ sk_adjust_memalloc(1, 1);
+ err = sk_set_vmio(sk);
+ } else if (client->cl_xprt->swapper) {
+ client->cl_xprt->swapper = 0;
+ sk_adjust_memalloc(-1, -1);
+ err = sk_clear_vmio(sk);
+ }
+
+ return err;
}

const struct address_space_operations nfs_file_aops = {
Index: linux-2.6/net/sunrpc/xprtsock.c
===================================================================
--- linux-2.6.orig/net/sunrpc/xprtsock.c
+++ linux-2.6/net/sunrpc/xprtsock.c
@@ -1014,6 +1014,7 @@ static void xs_udp_connect_worker(void *
{
struct rpc_xprt *xprt = (struct rpc_xprt *) args;
struct socket *sock = xprt->sock;
+ unsigned long pflags = current->flags;
int err, status = -EIO;

if (xprt->shutdown || xprt->addr.sin_port == 0)
@@ -1021,6 +1022,9 @@ static void xs_udp_connect_worker(void *

dprintk("RPC: xs_udp_connect_worker for xprt %p\n", xprt);

+ if (xprt->swapper)
+ current->flags |= PF_MEMALLOC;
+
/* Start by resetting any existing state */
xs_close(xprt);

@@ -1054,6 +1058,9 @@ static void xs_udp_connect_worker(void *
xprt->sock = sock;
xprt->inet = sk;

+ if (xprt->swapper)
+ sk_set_vmio(sk);
+
write_unlock_bh(&sk->sk_callback_lock);
}
xs_udp_do_set_buffer_size(xprt);
@@ -1061,6 +1068,7 @@ static void xs_udp_connect_worker(void *
out:
xprt_wake_pending_tasks(xprt, status);
xprt_clear_connecting(xprt);
+ current->flags = pflags;
}

/*
@@ -1097,11 +1105,15 @@ static void xs_tcp_connect_worker(void *
{
struct rpc_xprt *xprt = (struct rpc_xprt *)args;
struct socket *sock = xprt->sock;
+ unsigned long pflags = current->flags;
int err, status = -EIO;

if (xprt->shutdown || xprt->addr.sin_port == 0)
goto out;

+ if (xprt->swapper)
+ current->flags |= PF_MEMALLOC;
+
dprintk("RPC: xs_tcp_connect_worker for xprt %p\n", xprt);

if (!xprt->sock) {
@@ -1170,10 +1182,14 @@ static void xs_tcp_connect_worker(void *
break;
}
}
+
+ if (xprt->swapper)
+ sk_set_vmio(xprt->inet);
out:
xprt_wake_pending_tasks(xprt, status);
out_clear:
xprt_clear_connecting(xprt);
+ current->flags = pflags;
}

/**
Index: linux-2.6/include/linux/sunrpc/xprt.h
===================================================================
--- linux-2.6.orig/include/linux/sunrpc/xprt.h
+++ linux-2.6/include/linux/sunrpc/xprt.h
@@ -147,7 +147,9 @@ struct rpc_xprt {
unsigned int max_reqs; /* total slots */
unsigned long state; /* transport state */
unsigned char shutdown : 1, /* being shut down */
- resvport : 1; /* use a reserved port */
+ resvport : 1, /* use a reserved port */
+ swapper : 1; /* we're swapping over this
+ transport */

/*
* XID
-
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