2021-07-26 12:06:36

by trondmy

[permalink] [raw]
Subject: [PATCH] SUNRPC/xprtrdma: Fix reconnection locking

From: Trond Myklebust <[email protected]>

The xprtrdma client code currently relies on the task that initiated the
connect to hold the XPRT_LOCK for the duration of the connection
attempt. If the task is woken early, due to some other event, then that
lock could get released early.
Avoid races by using the same mechanism that the socket code uses of
transferring lock ownership to the RDMA connect worker itself. That
frees us to call rpcrdma_xprt_disconnect() directly since we're now
guaranteed exclusion w.r.t. other callers.

Fixes: 4cf44be6f1e8 ("xprtrdma: Fix recursion into rpcrdma_xprt_disconnect()")
Signed-off-by: Trond Myklebust <[email protected]>
---
net/sunrpc/xprt.c | 2 ++
net/sunrpc/xprtrdma/transport.c | 11 +++++------
2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index aae5a328b15b..b88ac8132054 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -877,6 +877,7 @@ bool xprt_lock_connect(struct rpc_xprt *xprt,
spin_unlock(&xprt->transport_lock);
return ret;
}
+EXPORT_SYMBOL_GPL(xprt_lock_connect);

void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
{
@@ -893,6 +894,7 @@ void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
spin_unlock(&xprt->transport_lock);
wake_up_bit(&xprt->state, XPRT_LOCKED);
}
+EXPORT_SYMBOL_GPL(xprt_unlock_connect);

/**
* xprt_connect - schedule a transport connect operation
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 9c2ffc67c0fd..975aef16ad34 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -250,12 +250,9 @@ xprt_rdma_connect_worker(struct work_struct *work)
xprt->stat.connect_start;
xprt_set_connected(xprt);
rc = -EAGAIN;
- } else {
- /* Force a call to xprt_rdma_close to clean up */
- spin_lock(&xprt->transport_lock);
- set_bit(XPRT_CLOSE_WAIT, &xprt->state);
- spin_unlock(&xprt->transport_lock);
- }
+ } else
+ rpcrdma_xprt_disconnect(r_xprt);
+ xprt_unlock_connect(xprt, r_xprt);
xprt_wake_pending_tasks(xprt, rc);
}

@@ -489,6 +486,8 @@ xprt_rdma_connect(struct rpc_xprt *xprt, struct rpc_task *task)
struct rpcrdma_ep *ep = r_xprt->rx_ep;
unsigned long delay;

+ WARN_ON_ONCE(!xprt_lock_connect(xprt, task, r_xprt));
+
delay = 0;
if (ep && ep->re_connect_status != 0) {
delay = xprt_reconnect_delay(xprt);
--
2.31.1


2021-07-26 14:17:46

by Chuck Lever III

[permalink] [raw]
Subject: Re: [PATCH] SUNRPC/xprtrdma: Fix reconnection locking



> On Jul 26, 2021, at 8:03 AM, [email protected] wrote:
>
> From: Trond Myklebust <[email protected]>
>
> The xprtrdma client code currently relies on the task that initiated the
> connect to hold the XPRT_LOCK for the duration of the connection
> attempt. If the task is woken early, due to some other event, then that
> lock could get released early.
> Avoid races by using the same mechanism that the socket code uses of
> transferring lock ownership to the RDMA connect worker itself. That
> frees us to call rpcrdma_xprt_disconnect() directly since we're now
> guaranteed exclusion w.r.t. other callers.
>
> Fixes: 4cf44be6f1e8 ("xprtrdma: Fix recursion into rpcrdma_xprt_disconnect()")
> Signed-off-by: Trond Myklebust <[email protected]>

I would like to test this change with disconnect injection
before it is merged.


> ---
> net/sunrpc/xprt.c | 2 ++
> net/sunrpc/xprtrdma/transport.c | 11 +++++------
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index aae5a328b15b..b88ac8132054 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -877,6 +877,7 @@ bool xprt_lock_connect(struct rpc_xprt *xprt,
> spin_unlock(&xprt->transport_lock);
> return ret;
> }
> +EXPORT_SYMBOL_GPL(xprt_lock_connect);
>
> void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
> {
> @@ -893,6 +894,7 @@ void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
> spin_unlock(&xprt->transport_lock);
> wake_up_bit(&xprt->state, XPRT_LOCKED);
> }
> +EXPORT_SYMBOL_GPL(xprt_unlock_connect);
>
> /**
> * xprt_connect - schedule a transport connect operation
> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
> index 9c2ffc67c0fd..975aef16ad34 100644
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -250,12 +250,9 @@ xprt_rdma_connect_worker(struct work_struct *work)
> xprt->stat.connect_start;
> xprt_set_connected(xprt);
> rc = -EAGAIN;
> - } else {
> - /* Force a call to xprt_rdma_close to clean up */
> - spin_lock(&xprt->transport_lock);
> - set_bit(XPRT_CLOSE_WAIT, &xprt->state);
> - spin_unlock(&xprt->transport_lock);
> - }
> + } else
> + rpcrdma_xprt_disconnect(r_xprt);
> + xprt_unlock_connect(xprt, r_xprt);
> xprt_wake_pending_tasks(xprt, rc);
> }
>
> @@ -489,6 +486,8 @@ xprt_rdma_connect(struct rpc_xprt *xprt, struct rpc_task *task)
> struct rpcrdma_ep *ep = r_xprt->rx_ep;
> unsigned long delay;
>
> + WARN_ON_ONCE(!xprt_lock_connect(xprt, task, r_xprt));
> +
> delay = 0;
> if (ep && ep->re_connect_status != 0) {
> delay = xprt_reconnect_delay(xprt);
> --
> 2.31.1
>

--
Chuck Lever