[Sorry about the duplicate mail, Thomas: I got the netdev address
wrong on the first try.]
lockdep reported a circular dependency between cb_mutex and
genl_mutex, as follows:
-> #1 (nlk->cb_mutex){--..}:
[<c0127b5d>] __lock_acquire+0x9c8/0xb98
[<c01280f6>] lock_acquire+0x5d/0x75
[<c027adc1>] __mutex_lock_slowpath+0xdb/0x247
[<c027af49>] mutex_lock+0x1c/0x1f
[<c0236aa0>] netlink_dump_start+0xa9/0x12f
---> takes cb_mutex
[<c0237fa6>] genl_rcv_msg+0xa3/0x14c
[<c0235aa5>] netlink_run_queue+0x6f/0xe1
[<c0237772>] genl_rcv+0x2d/0x4e
---> trylocks genl_mutex
[<c0235ef0>] netlink_data_ready+0x15/0x55
[<c0234e98>] netlink_sendskb+0x1f/0x36
[<c0235772>] netlink_unicast+0x1a6/0x1c0
[<c0235ecf>] netlink_sendmsg+0x238/0x244
[<c021a92e>] sock_sendmsg+0xcb/0xe4
[<c021aa98>] sys_sendmsg+0x151/0x1af
[<c021b850>] sys_socketcall+0x203/0x222
[<c01025d2>] syscall_call+0x7/0xb
[<ffffffff>] 0xffffffff
-> #0 (genl_mutex){--..}:
[<c0127a46>] __lock_acquire+0x8b1/0xb98
[<c01280f6>] lock_acquire+0x5d/0x75
[<c027adc1>] __mutex_lock_slowpath+0xdb/0x247
[<c027af49>] mutex_lock+0x1c/0x1f
[<c023717d>] genl_lock+0xd/0xf
[<c023806f>] ctrl_dumpfamily+0x20/0xdd
---> takes genl_mutex
[<c0234bfa>] netlink_dump+0x50/0x168
---> takes cb_mutex
[<c02360f2>] netlink_recvmsg+0x15f/0x22f
[<c021a84a>] sock_recvmsg+0xd5/0xee
[<c021b24e>] sys_recvmsg+0xf5/0x187
[<c021b865>] sys_socketcall+0x218/0x222
[<c01025d2>] syscall_call+0x7/0xb
[<ffffffff>] 0xffffffff
The "trylock" in genl_rcv doesn't prevent the deadlock, because
it's not the last lock acquired. Perhaps this can be fixed by
not acquiring the genl_mutex in ctrl_dumpfamily; it silences
lockdep, at least. It is not clear to me what the value of
taking the mutex is there.
If this is an appropriate fix, here is a patch for it.
Signed-off-by: Ben Pfaff <[EMAIL PROTECTED]>
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 8c11ca4..2e79035 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -616,9 +616,6 @@ static int ctrl_dumpfamily(struct sk_buff *skb, struct
netlink_callback *cb)
int chains_to_skip = cb->args[0];
int fams_to_skip = cb->args[1];
- if (chains_to_skip != 0)
- genl_lock();
-
for (i = 0; i < GENL_FAM_TAB_SIZE; i++) {
if (i < chains_to_skip)
continue;
@@ -636,9 +633,6 @@ static int ctrl_dumpfamily(struct sk_buff *skb, struct
netlink_callback *cb)
}
errout:
- if (chains_to_skip != 0)
- genl_unlock();
-
cb->args[0] = i;
cb->args[1] = n;
--
Ben Pfaff
Nicira Networks, Inc.
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