gfapi: Fix IO error caused when there is consecutive graph switches

Issue:
Consider a simple situation, where glfs_init() is done, i.e. initial
graph is up. Now perform 2 volume sets that results in 2 client side
graph changes. After this perform some IO, the IO fails with ENOTCON.
The only way to recover this client is i guess another graph switch
or restart.

What actually is happening from code perspective:
Initial graph lets say A, followed by 2 consecutive graph switches
to B and C without any IO those two switches.

- graph_setup (A) as a result of GF_EVENT_CHILD_UP, and
fs->next_subvol = A

- glfs_init() results in fs->active_subvol = A, fs->next_subvol = NULL

- graph_setup (B) as a result of GF_EVENT_CHILD_UP, and
fs->next_subvol = B

- graph_setup (C) as a result of GF_EVENT_CHILD_UP, and
fs->next_subvol = C. It also sees that the previous graph B was never
set as fs->active_subvol, i.e. no IO or anything happened on B, so
can safely send GF_EVENT_PARENT_DOWN (by calling glfs_subvol_done(B)).
This parent down on B, results in child_down(B), which is fine.
But child_down also triggers graph_setup(B).

- graph_setup(B) as a result of GF_EVENT_CHILD_DOWN, and
fs->next_subvol = B, and GF_EVENT_PARENT_DOWN on C as explained
above. This again leads to GF_EVENT_CHILD_DOWN on C.

- graph_setup(C) as a result of GF_EVENT_CHILD_DOWN, and
fs->next_subvol = C, and GF_EVENT_PARENT_DOWN on B as explained
above.

Thus both the graphs B and C are disconnected, and hence the ENOTCON

Solution:
Remove the call to graph_setup() when the event is GF_EVENT_CHILD_DOWN.
It don't see any reason why graph_setup should be called when there is
child_down. Not sure what the original reason was, to have graph_setup
in child_down. git hostory shows the first patch itself had this call.

> Reviewed-on: http://review.gluster.org/14656
> Smoke: Gluster Build System <jenkins@build.gluster.org>
> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
> Reviewed-by: Jeff Darcy <jdarcy@redhat.com>

BUG: 1367294
Change-Id: I9de86555f66cc94a05649ac863b40ed3426ffd4b
Signed-off-by: Poornima G <pgurusid@redhat.com>
Signed-off-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Reviewed-on: http://review.gluster.org/14835
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Kaushal M <kaushal@redhat.com>

1 files changed, 0 insertions, 1 deletions

diff --git a/api/src/glfs-master.c b/api/src/glfs-master.c
index 77e2d53abb9..b49ce2c8447 100644
--- a/api/src/glfs-master.c
+++ b/api/src/glfs-master.c
@@ -110,7 +110,6 @@ notify (xlator_t *this, int event, void *data, ...)
                         pthread_cond_broadcast (&fs->child_down_cond);
                 }
                 pthread_mutex_unlock (&fs->mutex);
-		graph_setup (fs, graph);
 		glfs_init_done (fs, 1);
 		break;
 	case GF_EVENT_CHILD_CONNECTING: