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authorDavid Vrabel <david.vrabel@citrix.com>2016-09-19 13:58:30 +0100
committerAnna Schumaker <Anna.Schumaker@Netapp.com>2016-09-19 13:21:36 -0400
commitd48f9ce73c997573e1b512893fa6eddf353a6f69 (patch)
tree4020592abd7afd7d325b4f5a125641a613850285
parentca440c383a588091cae9fbce610b86a6e9d961ad (diff)
sunrpc: fix write space race causing stalls
Write space becoming available may race with putting the task to sleep in xprt_wait_for_buffer_space(). The existing mechanism to avoid the race does not work. This (edited) partial trace illustrates the problem: [1] rpc_task_run_action: task:43546@5 ... action=call_transmit [2] xs_write_space <-xs_tcp_write_space [3] xprt_write_space <-xs_write_space [4] rpc_task_sleep: task:43546@5 ... [5] xs_write_space <-xs_tcp_write_space [1] Task 43546 runs but is out of write space. [2] Space becomes available, xs_write_space() clears the SOCKWQ_ASYNC_NOSPACE bit. [3] xprt_write_space() attemts to wake xprt->snd_task (== 43546), but this has not yet been queued and the wake up is lost. [4] xs_nospace() is called which calls xprt_wait_for_buffer_space() which queues task 43546. [5] The call to sk->sk_write_space() at the end of xs_nospace() (which is supposed to handle the above race) does not call xprt_write_space() as the SOCKWQ_ASYNC_NOSPACE bit is clear and thus the task is not woken. Fix the race by resetting the SOCKWQ_ASYNC_NOSPACE bit in xs_nospace() so the second call to sk->sk_write_space() calls xprt_write_space(). Suggested-by: Trond Myklebust <trondmy@primarydata.com> Signed-off-by: David Vrabel <david.vrabel@citrix.com> cc: stable@vger.kernel.org # 4.4 Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
-rw-r--r--net/sunrpc/xprtsock.c11
1 files changed, 10 insertions, 1 deletions
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index bde39f2ff6e5..0137af1c0916 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -473,7 +473,16 @@ static int xs_nospace(struct rpc_task *task)
spin_unlock_bh(&xprt->transport_lock);
/* Race breaker in case memory is freed before above code is called */
- sk->sk_write_space(sk);
+ if (ret == -EAGAIN) {
+ struct socket_wq *wq;
+
+ rcu_read_lock();
+ wq = rcu_dereference(sk->sk_wq);
+ set_bit(SOCKWQ_ASYNC_NOSPACE, &wq->flags);
+ rcu_read_unlock();
+
+ sk->sk_write_space(sk);
+ }
return ret;
}