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Date: Wed, 28 Apr 2010 07:38:22 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Cong Wang <amwang@...hat.com>
Cc: Dave Jones <davej@...hat.com>, Miles Lane <miles.lane@...il.com>,
Greg Kroah-Hartman <gregkh@...e.de>,
LKML <linux-kernel@...r.kernel.org>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: 2.6.34-rc5-git7 -- INFO: possible circular locking dependency detected - &per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at: [<ffffffff8139f077>] lock_policy_rwsem_read+0x4a/0x7a
Cong Wang <amwang@...hat.com> writes:
> (Adding Eric B. into Cc.)
>
> Dave Jones wrote:
>> On Mon, Apr 26, 2010 at 09:30:41PM -0400, Miles Lane wrote:
>> > Dave, is this the same? http://marc.info/?l=linux-kernel&m=127207512031810&w=2
>>
>> looks like it to me. 499bca9b6d3243f9278a1f5a22d00e67acdd844d should have fixed it,
>> but it looks like that's present in -git7, so something is still missing..
>>
>> Dave
>>
>> > I produced this one by running "find /sys | xargs cat"
>> > > [ 2982.773548] [ INFO: possible circular locking dependency detected ]
>> > [ 2982.773551] 2.6.34-rc5-git7 #33
>> > [ 2982.773554] -------------------------------------------------------
>> > [ 2982.773557] head/6335 is trying to acquire lock:
>> > [ 2982.773560] (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}, at:
>> > [<ffffffff8139f077>] lock_policy_rwsem_read+0x4a/0x7a
>> > [ 2982.773571]
>> > [ 2982.773572] but task is already holding lock:
>> > [ 2982.773575] (s_active#102){++++.+}, at: [<ffffffff81153a23>]
>> > sysfs_read_file+0x8d/0x139
>> > [ 2982.773586]
>> > [ 2982.773586] which lock already depends on the new lock.
>> > [ 2982.773587]
>> > [ 2982.773590]
>> > [ 2982.773591] the existing dependency chain (in reverse order) is:
>> > [ 2982.773593]
>> > [ 2982.773594] -> #2 (s_active#102){++++.+}:
>> > [ 2982.773601] [<ffffffff8107654d>] __lock_acquire+0xb59/0xd11
>> > [ 2982.773608] [<ffffffff8107681a>] lock_acquire+0x115/0x150
>> > [ 2982.773613] [<ffffffff81154556>] sysfs_deactivate+0x9b/0xec
>> > [ 2982.773619] [<ffffffff81154d0a>] sysfs_addrm_finish+0x31/0x50
>> > [ 2982.773624] [<ffffffff81152e05>] sysfs_hash_and_remove+0x4e/0x65
>> > [ 2982.773629] [<ffffffff81155fc0>] sysfs_remove_group+0x8c/0xc5
>> > [ 2982.773634] [<ffffffffa00a3d26>]
>> > cpufreq_governor_dbs+0x2a6/0x33c [cpufreq_ondemand]
>> > [ 2982.773642] [<ffffffff8139da32>] __cpufreq_governor+0x5d/0xa3
>> > [ 2982.773648] [<ffffffff8139e4e2>] __cpufreq_remove_dev+0x231/0x2e2
>> > [ 2982.773653] [<ffffffff81454e40>] cpufreq_cpu_callback+0x62/0x7a
>> > [ 2982.773660] [<ffffffff8145d636>] notifier_call_chain+0x63/0x97
>> > [ 2982.773666] [<ffffffff810680dc>] __raw_notifier_call_chain+0x9/0xb
>> > [ 2982.773672] [<ffffffff8144337b>] _cpu_down+0x90/0x29e
>> > [ 2982.773679] [<ffffffff81048cd7>] disable_nonboot_cpus+0x6f/0x105
>> > [ 2982.773685] [<ffffffff81083b94>] suspend_devices_and_enter+0xe8/0x1ec
>> > [ 2982.773691] [<ffffffff81083d72>] enter_state+0xda/0x12b
>> > [ 2982.773696] [<ffffffff810834d5>] state_store+0xb1/0xce
>> > [ 2982.773702] [<ffffffff811f2fb3>] kobj_attr_store+0x17/0x19
>> > [ 2982.773708] [<ffffffff8115395a>] sysfs_write_file+0x103/0x13f
>> > [ 2982.773713] [<ffffffff810fb933>] vfs_write+0xa9/0x106
>> > [ 2982.773719] [<ffffffff810fba46>] sys_write+0x45/0x69
>> > [ 2982.773723] [<ffffffff81009d82>] system_call_fastpath+0x16/0x1b
>> > [ 2982.773730]
>> > [ 2982.773731] -> #1 (dbs_mutex){+.+.+.}:
>> > [ 2982.773737] [<ffffffff8107654d>] __lock_acquire+0xb59/0xd11
>> > [ 2982.773742] [<ffffffff8107681a>] lock_acquire+0x115/0x150
>> > [ 2982.773747] [<ffffffff814582ce>] __mutex_lock_common+0x57/0x558
>> > [ 2982.773752] [<ffffffff81458875>] mutex_lock_nested+0x34/0x39
>> > [ 2982.773757] [<ffffffffa00a3af6>]
>> > cpufreq_governor_dbs+0x76/0x33c [cpufreq_ondemand]
>> > [ 2982.773763] [<ffffffff8139da32>] __cpufreq_governor+0x5d/0xa3
>> > [ 2982.773769] [<ffffffff8139e7ec>] __cpufreq_set_policy+0x1a8/0x222
>> > [ 2982.773774] [<ffffffff8139ecca>] store_scaling_governor+0x19f/0x1ed
>> > [ 2982.773779] [<ffffffff8139e622>] store+0x56/0x78
>> > [ 2982.773783] [<ffffffff8115395a>] sysfs_write_file+0x103/0x13f
>> > [ 2982.773788] [<ffffffff810fb933>] vfs_write+0xa9/0x106
>> > [ 2982.773793] [<ffffffff810fba46>] sys_write+0x45/0x69
>> > [ 2982.773798] [<ffffffff81009d82>] system_call_fastpath+0x16/0x1b
>> > [ 2982.773803]
>> > [ 2982.773804] -> #0 (&per_cpu(cpu_policy_rwsem, cpu)){+++++.}:
>> > [ 2982.773810] [<ffffffff810763f7>] __lock_acquire+0xa03/0xd11
>> > [ 2982.773815] [<ffffffff8107681a>] lock_acquire+0x115/0x150
>> > [ 2982.773820] [<ffffffff81458bba>] down_read+0x42/0x57
>> > [ 2982.773825] [<ffffffff8139f077>] lock_policy_rwsem_read+0x4a/0x7a
>> > [ 2982.773830] [<ffffffff8139f0d7>] show+0x30/0x69
>> > [ 2982.773835] [<ffffffff81153a4a>] sysfs_read_file+0xb4/0x139
>> > [ 2982.773840] [<ffffffff810fbb10>] vfs_read+0xa6/0x103
>> > [ 2982.773844] [<ffffffff810fbc23>] sys_read+0x45/0x69
>> > [ 2982.773849] [<ffffffff81009d82>] system_call_fastpath+0x16/0x1b
>> > [ 2982.773854]
>> > [ 2982.773855] other info that might help us debug this:
>> > [ 2982.773856]
>> > [ 2982.773860] 2 locks held by head/6335:
>> > [ 2982.773862] #0: (&buffer->mutex){+.+.+.}, at:
>> > [<ffffffff811539ca>] sysfs_read_file+0x34/0x139
>> > [ 2982.773871] #1: (s_active#102){++++.+}, at: [<ffffffff81153a23>]
>> > sysfs_read_file+0x8d/0x139
>> > [ 2982.773881]
>> > [ 2982.773882] stack backtrace:
>> > [ 2982.773886] Pid: 6335, comm: head Not tainted 2.6.34-rc5-git7 #33
>> > [ 2982.773889] Call Trace:
>> > [ 2982.773893] [<ffffffff810755c3>] print_circular_bug+0xa8/0xb7
>> > [ 2982.773893] [<ffffffff810763f7>] __lock_acquire+0xa03/0xd11
>> > [ 2982.773893] [<ffffffff810766f6>] ? __lock_acquire+0xd02/0xd11
>> > [ 2982.773893] [<ffffffff8139f077>] ? lock_policy_rwsem_read+0x4a/0x7a
>> > [ 2982.773893] [<ffffffff8107681a>] lock_acquire+0x115/0x150
>> > [ 2982.773893] [<ffffffff8139f077>] ? lock_policy_rwsem_read+0x4a/0x7a
>> > [ 2982.773893] [<ffffffff81458bba>] down_read+0x42/0x57
>> > [ 2982.773893] [<ffffffff8139f077>] ? lock_policy_rwsem_read+0x4a/0x7a
>> > [ 2982.773893] [<ffffffff81459cb9>] ? _raw_spin_unlock_irqrestore+0x87/0x95
>> > [ 2982.773893] [<ffffffff8139f077>] lock_policy_rwsem_read+0x4a/0x7a
>> > [ 2982.773893] [<ffffffff8139f0d7>] show+0x30/0x69
>> > [ 2982.773893] [<ffffffff81153a4a>] sysfs_read_file+0xb4/0x139
>> > [ 2982.773893] [<ffffffff810fbb10>] vfs_read+0xa6/0x103
>> > [ 2982.773893] [<ffffffff81074eae>] ? trace_hardirqs_on_caller+0x127/0x152
>> > [ 2982.773893] [<ffffffff810fbc23>] sys_read+0x45/0x69
>> > [ 2982.773893] [<ffffffff81009d82>] system_call_fastpath+0x16/0x1b
>>
>
> With Eric B.'s patch, lockdep will treat s_active as a rwsem too, thus causes
> this warning...
Something seems to be missing from the trace I was copied on, but this
appears to be a classic case of holding a lock over removing a sysfs
attribute that the sysfs attribute grabs in it's show or store method.
The kernel blocks when a sysfs attribute is removed waiting for all
in process readers and writers to finish. The removes the need for
nasty module refcounting, and concerns about data being accessed after
it has been freed.
Eric
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