diff options
| author | David Vrabel | 2016-09-19 13:58:30 +0100 |
|---|---|---|
| committer | Anna Schumaker | 2016-09-19 13:21:36 -0400 |
| commit | d48f9ce73c997573e1b512893fa6eddf353a6f69 (patch) | |
| tree | 4020592abd7afd7d325b4f5a125641a613850285 /net/sunrpc | |
| parent | ca440c383a588091cae9fbce610b86a6e9d961ad (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>
Diffstat (limited to 'net/sunrpc')
| -rw-r--r-- | net/sunrpc/xprtsock.c | 11 |
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; } |