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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Scott James Remnant <scott@ubuntu.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: 2.3.31++: Badness at kernel/softirq.c:143 due to new session leader connector
Date: Fri, 25 Sep 2009 11:23:03 +0200
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Cc: Matt Helsley <matthltc@us.ibm.com>,
       "David S. Miller" <davem@davemloft.net>,
       Evgeniy Polyakov <johnpol@2ka.mipt.ru>, Oleg Nesterov <oleg@tv-sign.ru>
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Scott,

I am using the proc connector for fork and exit tracking. With the latest git 
the new session leader connector(commit 02b51df1b07b4e9ca823c89284e704cadb323cd1 
proc connector: add event for process becoming session leader)
causes the following warning:

------------[ cut here ]------------
Badness at kernel/softirq.c:143
Modules linked in: tun bridge stp kvm sclp_cpi dm_multipath scsi_dh sunrpc ipv6 
qeth_l2 binfmt_misc dm_mod qeth ccwgroup
CPU: 7 Not tainted 2.6.31-selfgit-08936-g851b147-dirty #130
Process xzd (pid: 7189, task: 000000013d804758, ksp: 00000001329eddb8)
Krnl PSW : 0404c00180000000 00000000001481d4 (local_bh_enable+0xb0/0xe0)
           R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 EA:3
Krnl GPRS: 0000000000000000 0000000000fcdd68 0000000100000000 00000001329ee000
           00000000008268a8 0000000132980bb4 0000000000000000 0000000132980ac8
           0000000000000001 0000000132980ac8 0000000100000000 000000013db3a470
           0000000132980ac8 0000000000525de8 000000000048a946 00000001329edc58
Krnl Code: 00000000001481c6: e33002f00004       lg      %r3,752
           00000000001481cc: a7f4ffd8           brc     15,14817c
           00000000001481d0: a7f40001           brc     15,1481d2
          >00000000001481d4: a7280001           lhi     %r2,1
           00000000001481d8: 50201000           st      %r2,0(%r1)
           00000000001481dc: a7f4ffd0           brc     15,14817c
           00000000001481e0: c0e5fffe4b76       brasl   %r14,1118cc
           00000000001481e6: e33002f00004       lg      %r3,752
Call Trace:
([<000000013fe04100>] 0x13fe04100)
 [<000000000048a946>] sk_filter+0x9a/0xd0
 [<000000000049d938>] netlink_broadcast+0x2c0/0x53c
 [<00000000003ba9ae>] cn_netlink_send+0x272/0x2b0
 [<00000000003baef0>] proc_sid_connector+0xc4/0xd4
 [<0000000000142604>] __set_special_pids+0x58/0x90
 [<0000000000159938>] sys_setsid+0xb4/0xd8
 [<00000000001187fe>] sysc_noemu+0x10/0x16
 [<00000041616cb266>] 0x41616cb266
Last Breaking-Event-Address:
 [<00000000001481d0>] local_bh_enable+0xac/0xe0


The warning is
--->    WARN_ON_ONCE(in_irq() || irqs_disabled());

I think the problem is, that sys_setsid holds the tasklist_lock with 
spinlock_irq. while calling the connector.

Any ideas for a proper fix?


Christian