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

Peter Zijlstra
2006-08-25T20:36:22Z

On Fri, 2006-08-25 at 16:14 -0400, Trond Myklebust wrote:
> Grumble... If your patches are targetting NFS, could you please at the
> very least Cc nfs@lists.sourceforge.net and/or myself.

Sorry, will make sure you're on the CC list next round.

> On Fri, 2006-08-25 at 17:40 +0200, Peter Zijlstra wrote:
> > 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;
> > }
>
> This all belongs in net/sunrpc/xprtsock.c. The NFS code has no business
> screwing around with the internals of the sunrpc transport.

Ok, I'll make a function there, and call that.

> > 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;
> > }
>
> How does this guarantee that the socket reconnection won't fail?

I was afraid this might not be enough, I really have to go through the
network code.

> Also, what about the case of rpc_malloc()? Can't that cause rpciod to
> deadlock when you add NFS swap into the equation?

I will have to plead ignorance for now, I'll look into this on monday.
On first glance it looks like rpc_malloc could use an |__GFP_EMERG for
RPC_TASK_SWAPPER.