kernel_optimize_test/net
Herbert Xu d7811e623d [NET]: Drop tx lock in dev_watchdog_up
Fix lockdep warning with GRE, iptables and Speedtouch ADSL, PPP over ATM.

On Sat, Sep 02, 2006 at 08:39:28PM +0000, Krzysztof Halasa wrote:
> 
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> -------------------------------------------------------
> swapper/0 is trying to acquire lock:
>  (&dev->queue_lock){-+..}, at: [<c02c8c46>] dev_queue_xmit+0x56/0x290
> 
> but task is already holding lock:
>  (&dev->_xmit_lock){-+..}, at: [<c02c8e14>] dev_queue_xmit+0x224/0x290
> 
> which lock already depends on the new lock.

This turns out to be a genuine bug.  The queue lock and xmit lock are
intentionally taken out of order.  Two things are supposed to prevent
dead-locks from occuring:

1) When we hold the queue_lock we're supposed to only do try_lock on the
tx_lock.

2) We always drop the queue_lock after taking the tx_lock and before doing
anything else.

> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (&dev->_xmit_lock){-+..}:
>        [<c012e7b6>] lock_acquire+0x76/0xa0
>        [<c0336241>] _spin_lock_bh+0x31/0x40
>        [<c02d25a9>] dev_activate+0x69/0x120

This path obviously breaks assumption 1) and therefore can lead to ABBA
dead-locks.

I've looked at the history and there seems to be no reason for the lock
to be held at all in dev_watchdog_up.  The lock appeared in day one and
even there it was unnecessary.  In fact, people added __dev_watchdog_up
precisely in order to get around the tx lock there.

The function dev_watchdog_up is already serialised by rtnl_lock since
its only caller dev_activate is always called under it.

So here is a simple patch to remove the tx lock from dev_watchdog_up.
In 2.6.19 we can eliminate the unnecessary __dev_watchdog_up and
replace it with dev_watchdog_up.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
2006-09-18 00:22:30 -07:00
..
802 Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
8021q [VLAN]: Fix link state propagation 2006-07-24 13:52:13 -07:00
appletalk [NET]: Conversions from kmalloc+memset to k(z|c)alloc. 2006-07-21 14:51:30 -07:00
atm [ATM]: Compile error on ARM 2006-08-17 16:29:53 -07:00
ax25 [NET]: Conversions from kmalloc+memset to k(z|c)alloc. 2006-07-21 14:51:30 -07:00
bluetooth [Bluetooth] Correct RFCOMM channel MTU for broken implementations 2006-07-24 12:44:25 -07:00
bridge [BRIDGE]: random extra bytes on STP TCN packet 2006-09-17 23:21:08 -07:00
core [NEIGH]: neigh_table_clear() doesn't free stats 2006-09-17 23:21:01 -07:00
dccp [DCCP]: Fix CCID3 2006-08-26 23:40:50 -07:00
decnet [DECNET]: Fix for routing bug 2006-08-02 14:14:44 -07:00
econet [NET]: Conversions from kmalloc+memset to k(z|c)alloc. 2006-07-21 14:51:30 -07:00
ethernet Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
ieee80211 [PATCH] ieee80211: TKIP requires CRC32 2006-07-27 14:37:31 -04:00
ipv4 [TCP] tcp-lp: bug fix for oops in 2.6.18-rc6 2006-09-17 23:21:09 -07:00
ipv6 [IPV6]: Accept -1 for IPV6_TCLASS 2006-09-17 23:21:08 -07:00
ipx [IPX]: Fix typo, ipxhdr() --> ipx_hdr() 2006-08-09 17:36:15 -07:00
irda [NET]: Conversions from kmalloc+memset to k(z|c)alloc. 2006-07-21 14:51:30 -07:00
key Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
lapb [LAPB]: Fix windowsize check 2006-08-05 21:15:58 -07:00
llc [LLC]: multicast receive device match 2006-08-13 18:56:26 -07:00
netfilter [NETFILTER]: ctnetlink: fix deadlock in table dumping 2006-08-17 18:12:38 -07:00
netlink [NETLINK]: Call panic if nl_table allocation fails 2006-08-29 21:22:18 -07:00
netrom [NETROM] lockdep: fix false positive 2006-07-12 13:59:02 -07:00
packet [PACKET]: Don't truncate non-linear skbs with mmaped IO 2006-09-17 23:59:57 -07:00
rose [ROSE] lockdep: fix false positive 2006-07-12 13:58:59 -07:00
rxrpc [NET]: Conversions from kmalloc+memset to k(z|c)alloc. 2006-07-21 14:51:30 -07:00
sched [NET]: Drop tx lock in dev_watchdog_up 2006-09-18 00:22:30 -07:00
sctp [SCTP]: Fix sctp_primitive_ABORT() call in sctp_close(). 2006-08-29 21:22:13 -07:00
sunrpc NFS: Check lengths more thoroughly in NFS4 readdir XDR decode 2006-08-24 15:53:34 -04:00
tipc [TIPC]: Removing useless casts 2006-07-21 15:52:20 -07:00
unix [AF_UNIX]: Kernel memory leak fix for af_unix datagram getpeersec patch 2006-08-02 14:12:06 -07:00
wanrouter [NET]: Conversions from kmalloc+memset to k(z|c)alloc. 2006-07-21 14:51:30 -07:00
x25 Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
xfrm [IPSEC]: Validate properly in xfrm_dst_check() 2006-08-13 18:55:53 -07:00
compat.c [NETFILTER]: iptables 32bit compat layer 2006-04-01 02:25:19 -08:00
Kconfig [NET]: Mark frame diverter for future removal. 2006-09-17 23:21:14 -07:00
Makefile
nonet.c [PATCH] Make most file operations structs in fs/ const 2006-03-28 09:16:06 -08:00
socket.c [NET]: Rate limiting for socket allocation failure messages. 2006-08-31 15:21:50 -07:00
sysctl_net.c Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
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