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author | J. Bruce Fields <bfields@redhat.com> | 2019-01-11 15:36:40 -0500 |
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committer | J. Bruce Fields <bfields@redhat.com> | 2019-02-06 15:37:14 -0500 |
commit | 95503d295ad6af20f09efff193e085481a962fd2 (patch) | |
tree | a580f60a4a517c73575705c1745de208840f1c43 /net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | |
parent | 66c898caefd346a88fbef242eb7892fd959308f6 (diff) | |
download | linux-95503d295ad6af20f09efff193e085481a962fd2.tar.gz linux-95503d295ad6af20f09efff193e085481a962fd2.tar.bz2 linux-95503d295ad6af20f09efff193e085481a962fd2.zip |
svcrpc: fix unlikely races preventing queueing of sockets
In the rpc server, When something happens that might be reason to wake
up a thread to do something, what we do is
- modify xpt_flags, sk_sock->flags, xpt_reserved, or
xpt_nr_rqsts to indicate the new situation
- call svc_xprt_enqueue() to decide whether to wake up a thread.
svc_xprt_enqueue may require multiple conditions to be true before
queueing up a thread to handle the xprt. In the SMP case, one of the
other CPU's may have set another required condition, and in that case,
although both CPUs run svc_xprt_enqueue(), it's possible that neither
call sees the writes done by the other CPU in time, and neither one
recognizes that all the required conditions have been set. A socket
could therefore be ignored indefinitely.
Add memory barries to ensure that any svc_xprt_enqueue() call will
always see the conditions changed by other CPUs before deciding to
ignore a socket.
I've never seen this race reported. In the unlikely event it happens,
another event will usually come along and the problem will fix itself.
So I don't think this is worth backporting to stable.
Chuck tried this patch and said "I don't see any performance
regressions, but my server has only a single last-level CPU cache."
Tested-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net/sunrpc/xprtrdma/svc_rdma_recvfrom.c')
-rw-r--r-- | net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c index 828b149eaaef..3ebb158c2279 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c @@ -314,8 +314,9 @@ static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc) spin_lock(&rdma->sc_rq_dto_lock); list_add_tail(&ctxt->rc_list, &rdma->sc_rq_dto_q); - spin_unlock(&rdma->sc_rq_dto_lock); + /* Note the unlock pairs with the smp_rmb in svc_xprt_ready: */ set_bit(XPT_DATA, &rdma->sc_xprt.xpt_flags); + spin_unlock(&rdma->sc_rq_dto_lock); if (!test_bit(RDMAXPRT_CONN_PENDING, &rdma->sc_flags)) svc_xprt_enqueue(&rdma->sc_xprt); goto out; |