rxrpc: Fix the keepalive generator [ver #2]

AF_RXRPC has a keepalive message generator that generates a message for a
peer ~20s after the last transmission to that peer to keep firewall ports
open.  The implementation is incorrect in the following ways:

 (1) It mixes up ktime_t and time64_t types.

 (2) It uses ktime_get_real(), the output of which may jump forward or
     backward due to adjustments to the time of day.

 (3) If the current time jumps forward too much or jumps backwards, the
     generator function will crank the base of the time ring round one slot
     at a time (ie. a 1s period) until it catches up, spewing out VERSION
     packets as it goes.

Fix the problem by:

 (1) Only using time64_t.  There's no need for sub-second resolution.

 (2) Use ktime_get_seconds() rather than ktime_get_real() so that time
     isn't perceived to go backwards.

 (3) Simplifying rxrpc_peer_keepalive_worker() by splitting it into two
     parts:

     (a) The "worker" function that manages the buckets and the timer.

     (b) The "dispatch" function that takes the pending peers and
     	 potentially transmits a keepalive packet before putting them back
     	 in the ring into the slot appropriate to the revised last-Tx time.

 (4) Taking everything that's pending out of the ring and splicing it into
     a temporary collector list for processing.

     In the case that there's been a significant jump forward, the ring
     gets entirely emptied and then the time base can be warped forward
     before the peers are processed.

     The warping can't happen if the ring isn't empty because the slot a
     peer is in is keepalive-time dependent, relative to the base time.

 (5) Limit the number of iterations of the bucket array when scanning it.

 (6) Set the timer to skip any empty slots as there's no point waking up if
     there's nothing to do yet.

This can be triggered by an incoming call from a server after a reboot with
AF_RXRPC and AFS built into the kernel causing a peer record to be set up
before userspace is started.  The system clock is then adjusted by
userspace, thereby potentially causing the keepalive generator to have a
meltdown - which leads to a message like:

	watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [kworker/0:1:23]
	...
	Workqueue: krxrpcd rxrpc_peer_keepalive_worker
	EIP: lock_acquire+0x69/0x80
	...
	Call Trace:
	 ? rxrpc_peer_keepalive_worker+0x5e/0x350
	 ? _raw_spin_lock_bh+0x29/0x60
	 ? rxrpc_peer_keepalive_worker+0x5e/0x350
	 ? rxrpc_peer_keepalive_worker+0x5e/0x350
	 ? __lock_acquire+0x3d3/0x870
	 ? process_one_work+0x110/0x340
	 ? process_one_work+0x166/0x340
	 ? process_one_work+0x110/0x340
	 ? worker_thread+0x39/0x3c0
	 ? kthread+0xdb/0x110
	 ? cancel_delayed_work+0x90/0x90
	 ? kthread_stop+0x70/0x70
	 ? ret_from_fork+0x19/0x24

Fixes: ace45bec6d77 ("rxrpc: Fix firewall route keepalive")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 5fb7d3254d9e..707630ab4713 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -104,9 +104,9 @@ struct rxrpc_net {
 
 #define RXRPC_KEEPALIVE_TIME 20 /* NAT keepalive time in seconds */
 	u8			peer_keepalive_cursor;
-	ktime_t			peer_keepalive_base;
-	struct hlist_head	peer_keepalive[RXRPC_KEEPALIVE_TIME + 1];
-	struct hlist_head	peer_keepalive_new;
+	time64_t		peer_keepalive_base;
+	struct list_head	peer_keepalive[32];
+	struct list_head	peer_keepalive_new;
 	struct timer_list	peer_keepalive_timer;
 	struct work_struct	peer_keepalive_work;
 };
@@ -295,7 +295,7 @@ struct rxrpc_peer {
 	struct hlist_head	error_targets;	/* targets for net error distribution */
 	struct work_struct	error_distributor;
 	struct rb_root		service_conns;	/* Service connections */
-	struct hlist_node	keepalive_link;	/* Link in net->peer_keepalive[] */
+	struct list_head	keepalive_link;	/* Link in net->peer_keepalive[] */
 	time64_t		last_tx_at;	/* Last time packet sent here */
 	seqlock_t		service_conn_lock;
 	spinlock_t		lock;		/* access lock */