linux-next - process hangs in do_exit().

[Valdis Kletnieks]

Saw my laptop grind to a halt this morning where processes would hang
while trying to exit.  Looks like Al was last person to touch kernel/acct.c
back around Jan 9:

commit 9e251d02041432487d89cb340e72490c4bbc198a
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Fri Jan 9 20:40:02 2015 -0500

    kill pin_put()

touched code near where it hung.  But I don't understand RCU enough to
tell for sure what is/isn't wrong there....

Found this in my syslog:

Jan 29 08:51:30 turing-police kernel: [36313.248179] INFO: task sendmail:32228 blocked for more than 120 seconds.
Jan 29 08:51:30 turing-police kernel: [36313.248192]       Tainted: G           OE   3.19.0-rc6-next-20150127 #42
Jan 29 08:51:30 turing-police kernel: [36313.248196] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jan 29 08:51:30 turing-police kernel: [36313.248200] sendmail        D ffff880098ddbd98 12880 32228   1380 0x00000080
Jan 29 08:51:30 turing-police kernel: [36313.248215]  ffff880098ddbd98 ffff880098ddbda8 ffff880098ddbfd8 ffff8801bd090c90
Jan 29 08:51:30 turing-police kernel: [36313.248226]  ffffffff9e0b34a1 0000000000014c80 ffff88022dd94c80 ffff88022cb2c350
Jan 29 08:51:30 turing-police kernel: [36313.248236]  ffff8801bd090c90 ffff880098ddbd88 ffff880222133e30 0000000000000200
Jan 29 08:51:30 turing-police kernel: [36313.248247] Call Trace:
Jan 29 08:51:30 turing-police kernel: [36313.248261]  [<ffffffff9e0b34a1>] ? acct_get+0x4f/0x76
Jan 29 08:51:30 turing-police kernel: [36313.248271]  [<ffffffff9e6c267f>] schedule+0x64/0x66
Jan 29 08:51:30 turing-police kernel: [36313.248279]  [<ffffffff9e6c29ad>] schedule_preempt_disabled+0x13/0x1f
Jan 29 08:51:30 turing-police kernel: [36313.248287]  [<ffffffff9e6c3db4>] mutex_lock_nested+0x274/0x58c
Jan 29 08:51:30 turing-police kernel: [36313.248293]  [<ffffffff9e0b34a1>] ? acct_get+0x4f/0x76
Jan 29 08:51:30 turing-police kernel: [36313.248300]  [<ffffffff9e0b3433>] ? rcu_read_unlock+0x3e/0x5d
Jan 29 08:51:30 turing-police kernel: [36313.248307]  [<ffffffff9e0b34a1>] acct_get+0x4f/0x76
Jan 29 08:51:30 turing-police kernel: [36313.248315]  [<ffffffff9e0b3e69>] acct_process+0x56/0x89
Jan 29 08:51:30 turing-police kernel: [36313.248324]  [<ffffffff9e042f68>] do_exit+0x55e/0xcf4
Jan 29 08:51:30 turing-police kernel: [36313.248332]  [<ffffffff9e0c8d68>] ? __audit_syscall_entry+0x10b/0x137
Jan 29 08:51:30 turing-police kernel: [36313.248341]  [<ffffffff9e00e35d>] ? do_audit_syscall_entry+0xb8/0xc7
Jan 29 08:51:30 turing-police kernel: [36313.248349]  [<ffffffff9e0448aa>] do_group_exit+0x63/0xe0
Jan 29 08:51:30 turing-police kernel: [36313.248356]  [<ffffffff9e044936>] SyS_exit_group+0xf/0xf
Jan 29 08:51:30 turing-police kernel: [36313.248363]  [<ffffffff9e6c8112>] system_call_fastpath+0x12/0x17

Jan 29 08:51:30 turing-police kernel: [36313.248369] INFO: lockdep is turned off.
Jan 29 08:51:30 turing-police kernel: [36313.248375] INFO: task formail:32242 blocked for more than 120 seconds.
Jan 29 08:51:30 turing-police kernel: [36313.248379]       Tainted: G           OE   3.19.0-rc6-next-20150127 #42
Jan 29 08:51:30 turing-police kernel: [36313.248383] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jan 29 08:51:30 turing-police kernel: [36313.248387] formail         D ffff8801882b7d98 14104 32242  32241 0x00000082
Jan 29 08:51:30 turing-police kernel: [36313.248399]  ffff8801882b7d98 ffff8801882b7da8 ffff8801882b7fd8 ffff8801c07e8cd0
Jan 29 08:51:30 turing-police kernel: [36313.248409]  ffffffff9e0b34a1 0000000000014c80 ffff88022dc94c80 ffff88022cb182d0
Jan 29 08:51:30 turing-police kernel: [36313.248419]  ffff8801c07e8cd0 ffff8801882b7d88 ffff880222133e30 0000000000000200
Jan 29 08:51:30 turing-police kernel: [36313.248429] Call Trace:
Jan 29 08:51:30 turing-police kernel: [36313.248436]  [<ffffffff9e0b34a1>] ? acct_get+0x4f/0x76
Jan 29 08:51:30 turing-police kernel: [36313.248444]  [<ffffffff9e6c267f>] schedule+0x64/0x66
Jan 29 08:51:30 turing-police kernel: [36313.248451]  [<ffffffff9e6c29ad>] schedule_preempt_disabled+0x13/0x1f
Jan 29 08:51:30 turing-police kernel: [36313.248459]  [<ffffffff9e6c3db4>] mutex_lock_nested+0x274/0x58c
Jan 29 08:51:30 turing-police kernel: [36313.248465]  [<ffffffff9e0b34a1>] ? acct_get+0x4f/0x76
Jan 29 08:51:30 turing-police kernel: [36313.248472]  [<ffffffff9e0b3433>] ? rcu_read_unlock+0x3e/0x5d
Jan 29 08:51:30 turing-police kernel: [36313.248479]  [<ffffffff9e0b34a1>] acct_get+0x4f/0x76
Jan 29 08:51:30 turing-police kernel: [36313.248485]  [<ffffffff9e0b3e69>] acct_process+0x56/0x89
Jan 29 08:51:30 turing-police kernel: [36313.248493]  [<ffffffff9e042f68>] do_exit+0x55e/0xcf4
Jan 29 08:51:30 turing-police kernel: [36313.248499]  [<ffffffff9e0c8d68>] ? __audit_syscall_entry+0x10b/0x137
Jan 29 08:51:30 turing-police kernel: [36313.248507]  [<ffffffff9e00e35d>] ? do_audit_syscall_entry+0xb8/0xc7
Jan 29 08:51:30 turing-police kernel: [36313.248514]  [<ffffffff9e0448aa>] do_group_exit+0x63/0xe0
Jan 29 08:51:30 turing-police kernel: [36313.248521]  [<ffffffff9e044936>] SyS_exit_group+0xf/0xf
Jan 29 08:51:30 turing-police kernel: [36313.248528]  [<ffffffff9e6c8112>] system_call_fastpath+0x12/0x17
Jan 29 08:51:30 turing-police kernel: [36313.248532] INFO: lockdep is turned off.
Jan 29 08:51:30 turing-police kernel: [36313.248537] INFO: task formail:32246 blocked for more than 120 seconds.
Jan 29 08:51:30 turing-police kernel: [36313.248541]       Tainted: G           OE   3.19.0-rc6-next-20150127 #42

(and another few identical traces)

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