On Wed, 2016-05-18 at 14:54 -0300, Paulo Andrade wrote:
> An user reports that their application connects to multiple servers
> through a rpc interface using libtirpc. When one of the servers misbehaves
> (goes down ungracefully or has a delay of a few seconds in the traffic
> flow), it was observed that the traffic from the client to other servers is
> decreased by the traffic anomaly of the failing server, i.e. traffic
> decreases or goes to 0 in all the servers.
>
> When investigated further, specifically into the behavior of the libtirpc
> at the time of the issue, it was observed that all of the application
> threads specifically interacting with libtirpc were locked into one single
> lock inside the libtirpc library. This was a race condition which had
> resulted in a deadlock and hence the resultant dip/stoppage of traffic.
>
> As an experiment, the user removed the libtirpc from the application build
> and used the standard glibc library for rpc communication. In that case,
> everything worked perfectly even in the time of the issue of server nodes
> misbehaving.
I recommend simplifying this.
It should be a concise description of what is wrong and how this patch resolves
it.
The description of the investigation will probably make reading the history more
difficult when trying to find changes at later times so less is more I think.
>
> Signed-off-by: Paulo Andrade <pcpa@xxxxxxx>
> ---
> src/clnt_vc.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/src/clnt_vc.c b/src/clnt_vc.c
> index a72f9f7..2396f34 100644
> --- a/src/clnt_vc.c
> +++ b/src/clnt_vc.c
> @@ -229,27 +229,23 @@ clnt_vc_create(fd, raddr, prog, vers, sendsz, recvsz)
> } else
> assert(vc_cv != (cond_t *) NULL);
>
> - /*
> - * XXX - fvdl connecting while holding a mutex?
> - */
> + mutex_unlock(&clnt_fd_lock);
> +
> slen = sizeof ss;
> if (getpeername(fd, (struct sockaddr *)&ss, &slen) < 0) {
> if (errno != ENOTCONN) {
> rpc_createerr.cf_stat = RPC_SYSTEMERROR;
> rpc_createerr.cf_error.re_errno = errno;-
> mutex_unlock(&clnt_fd_lock);
> thr_sigsetmask(SIG_SETMASK, &(mask), NULL);
> goto err;
> }
> if (connect(fd, (struct sockaddr *)raddr->buf, raddr->len) <
> 0){
> rpc_createerr.cf_stat = RPC_SYSTEMERROR;
> rpc_createerr.cf_error.re_errno = errno;
> - mutex_unlock(&clnt_fd_lock);
> thr_sigsetmask(SIG_SETMASK, &(mask), NULL);
> goto err;
> }
> }
> - mutex_unlock(&clnt_fd_lock);
> if (!__rpc_fd2sockinfo(fd, &si))
> goto err;
> thr_sigsetmask(SIG_SETMASK, &(mask), NULL);
We will need to review the code in the other clnt_*_create() functions for this
to be a complete resolution for the problem.
Ian
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