diff options
author | J. Bruce Fields <bfields@redhat.com> | 2015-10-09 01:44:07 +0000 |
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committer | J. Bruce Fields <bfields@redhat.com> | 2015-11-10 17:02:47 -0500 |
commit | 0442f14b15f8e7a8b3778a9f8cf640ef89b2df26 (patch) | |
tree | dd7cae613d5d154bd945b9c140d4764074bbbe08 /net | |
parent | 7fc0564e3a8d16df096f48c9c6425ba84d945c6e (diff) | |
download | op-kernel-dev-0442f14b15f8e7a8b3778a9f8cf640ef89b2df26.zip op-kernel-dev-0442f14b15f8e7a8b3778a9f8cf640ef89b2df26.tar.gz |
svcrpc: document lack of some memory barriers
We're missing memory barriers in net/sunrpc/svcsock.c in some spots we'd
expect them. But it doesn't appear they're necessary in our case, and
this is likely a hot path--for now just document the odd behavior.
Kosuke Tatsukawa found this issue while looking through the linux source
code for places calling waitqueue_active() before wake_up*(), but
without preceding memory barriers, after sending a patch to fix a
similar issue in drivers/tty/n_tty.c (Details about the original issue
can be found here: https://lkml.org/lkml/2015/9/28/849).
Reported-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net')
-rw-r--r-- | net/sunrpc/svcsock.c | 37 |
1 files changed, 31 insertions, 6 deletions
diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c index e0c7b33..1413cdc 100644 --- a/net/sunrpc/svcsock.c +++ b/net/sunrpc/svcsock.c @@ -399,6 +399,31 @@ static int svc_sock_secure_port(struct svc_rqst *rqstp) return svc_port_is_privileged(svc_addr(rqstp)); } +static bool sunrpc_waitqueue_active(wait_queue_head_t *wq) +{ + if (!wq) + return false; + /* + * There should normally be a memory * barrier here--see + * wq_has_sleeper(). + * + * It appears that isn't currently necessary, though, basically + * because callers all appear to have sufficient memory barriers + * between the time the relevant change is made and the + * time they call these callbacks. + * + * The nfsd code itself doesn't actually explicitly wait on + * these waitqueues, but it may wait on them for example in + * sendpage() or sendmsg() calls. (And those may be the only + * places, since it it uses nonblocking reads.) + * + * Maybe we should add the memory barriers anyway, but these are + * hot paths so we'd need to be convinced there's no sigificant + * penalty. + */ + return waitqueue_active(wq); +} + /* * INET callback when data has been received on the socket. */ @@ -414,7 +439,7 @@ static void svc_udp_data_ready(struct sock *sk) set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); svc_xprt_enqueue(&svsk->sk_xprt); } - if (wq && waitqueue_active(wq)) + if (sunrpc_waitqueue_active(wq)) wake_up_interruptible(wq); } @@ -432,7 +457,7 @@ static void svc_write_space(struct sock *sk) svc_xprt_enqueue(&svsk->sk_xprt); } - if (wq && waitqueue_active(wq)) { + if (sunrpc_waitqueue_active(wq)) { dprintk("RPC svc_write_space: someone sleeping on %p\n", svsk); wake_up_interruptible(wq); @@ -787,7 +812,7 @@ static void svc_tcp_listen_data_ready(struct sock *sk) } wq = sk_sleep(sk); - if (wq && waitqueue_active(wq)) + if (sunrpc_waitqueue_active(wq)) wake_up_interruptible_all(wq); } @@ -808,7 +833,7 @@ static void svc_tcp_state_change(struct sock *sk) set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags); svc_xprt_enqueue(&svsk->sk_xprt); } - if (wq && waitqueue_active(wq)) + if (sunrpc_waitqueue_active(wq)) wake_up_interruptible_all(wq); } @@ -823,7 +848,7 @@ static void svc_tcp_data_ready(struct sock *sk) set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); svc_xprt_enqueue(&svsk->sk_xprt); } - if (wq && waitqueue_active(wq)) + if (sunrpc_waitqueue_active(wq)) wake_up_interruptible(wq); } @@ -1593,7 +1618,7 @@ static void svc_sock_detach(struct svc_xprt *xprt) sk->sk_write_space = svsk->sk_owspace; wq = sk_sleep(sk); - if (wq && waitqueue_active(wq)) + if (sunrpc_waitqueue_active(wq)) wake_up_interruptible(wq); } |