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Re: [Cluster-devel] [PATCH] rgmanager: Halt services if CMAN dies



Looks sane to me.

Fabio

On 10/27/2010 11:17 PM, Lon Hohberger wrote:
> If cman dies because it receives a kill packet (of doom)
> from other hosts, rgmanager does not notice.  This can
> happen if, for example, you are using qdiskd and it hangs
> on I/O to the quorum disk due to frequent trespasses or
> other SAN interruptions.  The other instance of qdiskd
> will ask CMAN to evict the hung node, causing it to be
> ejected from the cluster and fenced.
> 
> Data is safe (which is the top priority).  If power-cycle
> fencing is in use, there is no issue at all; the node
> reboots and service failover occurs fairly quickly.
> 
> However, problems can arise if, in the same hung-I/O
> situation:
> 
>  * storage-level fencing is in use
> 
>  * rgmanager has one or more IP addresses in use
>    as part of cluster services.
> 
> This is because more recent versions of the IP resource
> agent actually ping the IP address prior to bringing it
> online for use by services.  This prevents accidental
> take-over of IP addresses in use by other hosts on the
> network due to an administrator mistake when setting up
> the cluster.
> 
> Unfortunately, this behavior also prevents service
> failover if the presumed-dead host is still online.
> 
> This patch causes rgmanager to use poll() instead of
> select() when dealing with the baseline CMAN connection
> it uses for receiving membership changes and so forth.
> 
> If the socket is closed by CMAN (either by CMAN's death
> or some other reason), rgmanager can now detect and act
> upon that will now treat that stimulus.  It treats it as
> an emergency cluster shutdown request.  It will halt all
> services and exit as quickly as possible.
> 
> Unfortunately, there is a race between this emergency
> action and recovery on the surviving host.  It is not
> possible for rgmanager to guarantee that all services will
> halt after the node has been fenced from shared storage
> (but before the other host attempts to start the
> service(s)).
> 
> Furthermore, a hung 'stop' request caused by loss of
> access to shared storage may very well cause rgmanager
> to hang forever, preventing some services (or parts)
> from ever actually being killed.
> 
> A main use case for storage-level fencing over power-
> cycling is the ability to perform post-mortem RCA of what
> happened in order to cause the node to die in the first
> place.  This implies that rgmanager killing the host
> would be an incorrect resolution.
> 
> Resolves: rhbz#639961
> 
> Signed-off-by: Lon Hohberger <lhh redhat com>
> ---
>  rgmanager/src/clulib/msg_cluster.c |   32 ++++++++++++++++++++++----------
>  1 files changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/rgmanager/src/clulib/msg_cluster.c b/rgmanager/src/clulib/msg_cluster.c
> index 4ec3750..00f28c3 100644
> --- a/rgmanager/src/clulib/msg_cluster.c
> +++ b/rgmanager/src/clulib/msg_cluster.c
> @@ -34,7 +34,9 @@
>  #include <gettid.h>
>  #include <cman-private.h>
>  #include <clulog.h>
> +#include <poll.h>
>  
> +static void process_cman_event(cman_handle_t handle, void *private, int reason, int arg);
>  /* Ripped from ccsd's setup_local_socket */
>  
>  int cluster_msg_close(msgctx_t *ctx);
> @@ -165,18 +167,17 @@ static int
>  poll_cluster_messages(int timeout)
>  {
>  	int ret = -1;
> -	fd_set rfds;
> -	int fd, lfd, max;
> +	int fd, lfd;
>  	struct timeval tv;
>  	struct timeval *p = NULL;
>  	cman_handle_t ch;
> +	struct pollfd fds[2];
>  
>  	if (timeout >= 0) {
>  		p = &tv;
>  		tv.tv_sec = tv.tv_usec = timeout;
>  	}
>  
> -	FD_ZERO(&rfds);
>  
>  	/* This sucks - it could cause other threads trying to get a
>  	   membership list to block for a long time.  Now, that should not
> @@ -195,20 +196,31 @@ poll_cluster_messages(int timeout)
>  		cman_unlock(ch);
>  		return 0;
>  	}
> -	FD_SET(fd, &rfds);
> -	FD_SET(lfd, &rfds);
>  
> -	max = (lfd > fd ? lfd : fd);
> -	if (select(max + 1, &rfds, NULL, NULL, p) > 0) {
> +	fds[0].fd = lfd;
> +	fds[1].fd = fd;
> +	fds[0].events = POLLIN | POLLHUP | POLLERR;
> +	fds[1].events = POLLIN | POLLHUP | POLLERR;
> +
> +	if (poll(fds, 2, timeout * 1000) > 0) {
> +
>  		/* Someone woke us up */
> -		if (FD_ISSET(lfd, &rfds)) {
> +		if (fds[0].revents & POLLIN) {
>  			cman_unlock(ch);
>  			errno = EAGAIN;
>  			return -1;
>  		}
>  
> -		cman_dispatch(ch, 0);
> -		ret = 0;
> +		if (fds[1].revents & (POLLHUP | POLLERR)) {
> +			process_cman_event(ch, NULL,
> +					   CMAN_REASON_TRY_SHUTDOWN,
> +					   0);
> +		}
> +
> +		if (fds[1].revents & POLLIN) {
> +			cman_dispatch(ch, 0);
> +			ret = 0;
> +		}
>  	}
>  	cman_unlock(ch);
>  


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