[PATCH net-next 05/15] afs: Give an afs_server object a ref on the afs_cell object it points to

[David Howells <dhowells@redhat.com>]

Give an afs_server object a ref on the afs_cell object it points to so that
the cell doesn't get deleted before the server record.

Whilst this is circular (cell -> vol -> server_list -> server -> cell), the
ref only pins the memory, not the lifetime as that's controlled by the
activity counter.  When the volume's activity counter reaches 0, it
detaches from the cell and discards its server list; when a cell's activity
counter reaches 0, it discards its root volume.  At that point, the
circularity is broken.

Fixes: d2ddc776a458 ("afs: Overhaul volume and server record caching and fileserver rotation")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
---
 fs/afs/server.c            | 3 +++
 include/trace/events/afs.h | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/fs/afs/server.c b/fs/afs/server.c
index 038f9d0ae3af..4504e16b458c 100644
--- a/fs/afs/server.c
+++ b/fs/afs/server.c
@@ -163,6 +163,8 @@ static struct afs_server *afs_install_server(struct afs_cell *cell,
 	rb_insert_color(&server->uuid_rb, &net->fs_servers);
 	hlist_add_head_rcu(&server->proc_link, &net->fs_proc);
 
+	afs_get_cell(cell, afs_cell_trace_get_server);
+
 added_dup:
 	write_seqlock(&net->fs_addr_lock);
 	estate = rcu_dereference_protected(server->endpoint_state,
@@ -442,6 +444,7 @@ static void afs_server_rcu(struct rcu_head *rcu)
 			 atomic_read(&server->active), afs_server_trace_free);
 	afs_put_endpoint_state(rcu_access_pointer(server->endpoint_state),
 			       afs_estate_trace_put_server);
+	afs_put_cell(server->cell, afs_cell_trace_put_server);
 	kfree(server);
 }
 
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index b0db89058c91..958a2460330c 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -174,6 +174,7 @@ enum yfs_cm_operation {
 	EM(afs_cell_trace_get_queue_dns,	"GET q-dns ") \
 	EM(afs_cell_trace_get_queue_manage,	"GET q-mng ") \
 	EM(afs_cell_trace_get_queue_new,	"GET q-new ") \
+	EM(afs_cell_trace_get_server,		"GET server") \
 	EM(afs_cell_trace_get_vol,		"GET vol   ") \
 	EM(afs_cell_trace_insert,		"INSERT    ") \
 	EM(afs_cell_trace_manage,		"MANAGE    ") \
@@ -182,6 +183,7 @@ enum yfs_cm_operation {
 	EM(afs_cell_trace_put_destroy,		"PUT destry") \
 	EM(afs_cell_trace_put_queue_work,	"PUT q-work") \
 	EM(afs_cell_trace_put_queue_fail,	"PUT q-fail") \
+	EM(afs_cell_trace_put_server,		"PUT server") \
 	EM(afs_cell_trace_put_vol,		"PUT vol   ") \
 	EM(afs_cell_trace_see_source,		"SEE source") \
 	EM(afs_cell_trace_see_ws,		"SEE ws    ") \