From a1caec1f2bebe09f685716f13d7b55f84d8a8145 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Thu, 19 Nov 2020 13:48:14 +0100
Subject: [KERNEL] Fix several connect/disconnect race conditions

Previously disconnect was protected against concurrent calls, but connect
wasn't. It was easy to crash the kernel when calling connect and
disconnect IOCTLs in a tight loop concurrently.
A global lock was introduced to make sure only one caller can change the
connection state at a time. dev->connection_lock needs to be aquired
when calling dnbd3_net_connect or _disconnect.
This atomic_t based locking mechanism should be turned into a mutex in a
next step, relying on mutex_trylock for cases where we don't have the
cmpxchg-schedule() loop.

Along the way it was noticed that the send/receive timeouts don't apply
to kernel_connect, which might have been the case in older 3.x kernel
versions. A crude workaround using nonblocking connect has been
introduced to emulate this, but a clean solution for this is welcomed.

Also, devices are now properly closed on module unload.
---
 src/kernel/dnbd3_main.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'src/kernel/dnbd3_main.h')

diff --git a/src/kernel/dnbd3_main.h b/src/kernel/dnbd3_main.h
index a3c2828..ec8c8cf 100644
--- a/src/kernel/dnbd3_main.h
+++ b/src/kernel/dnbd3_main.h
@@ -62,7 +62,8 @@ typedef struct
 	dnbd3_server_t alt_servers[NUMBER_SERVERS]; // array of alt servers
 	int new_servers_num;	// number of new alt servers that are waiting to be copied to above array
 	dnbd3_server_entry_t new_servers[NUMBER_SERVERS]; // pending new alt servers
-	uint8_t discover, panic, disconnecting, update_available, panic_count;
+	uint8_t discover, panic, update_available, panic_count;
+	atomic_t connection_lock;
 	uint8_t use_server_provided_alts;
 	uint16_t rid;
 	uint32_t heartbeat_count;
-- 
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