Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2]

From: Prarit Bhargava
Date: Mon Aug 04 2014 - 11:05:21 EST



On 08/04/2014 10:00 AM, Prarit Bhargava wrote:

> There is an already reported LOCKDEP warning in the xfs code that fires at login
> so I know LOCKDEP is functional.
>

It turns out that the above was the problem. I didn't realize that LOCKDEP will
only report a single warning :(

[Aside: Is there a way to "re-arm" LOCKDEP?]

Reproduced on x86 and taking a further look:


[root@intel-canoepass-05 ~]# cd /sys/devices/system/cpu/cpu2/cpufreq/
[root@intel-canoepass-05 cpufreq]# cat conservative/*
20
5
0
1
20000
20000
80
[root@intel-canoepass-05 cpufreq]# echo ondemand > scaling_governor
[ 75.163583] cpufreq_set_policy: stopping governor conservative
[ 75.170348] cpufreq_governor_dbs: removing sysfs files for governor conservative
[ 75.178698]
[ 75.180364] ======================================================
[ 75.187271] [ INFO: possible circular locking dependency detected ]
[ 75.194278] 3.16.0-rc7+ #22 Not tainted
[ 75.198561] -------------------------------------------------------
[ 75.205564] bash/3131 is trying to acquire lock:
[ 75.210726] (s_active#219){++++.+}, at: [<ffffffff8126ce55>]
kernfs_remove_by_name_ns+0x45/0xa0
[ 75.220623]
[ 75.220623] but task is already holding lock:
[ 75.227141] (&policy->rwsem){+++++.}, at: [<ffffffff814ecab0>] store+0x60/0xc0
[ 75.235370]
[ 75.235370] which lock already depends on the new lock.
[ 75.235370]
[ 75.244509]
[ 75.244509] the existing dependency chain (in reverse order) is:
[ 75.252874]
-> #1 (&policy->rwsem){+++++.}:
[ 75.257785] [<ffffffff810cc892>] lock_acquire+0xa2/0x120
[ 75.264429] [<ffffffff8166ed40>] mutex_lock_nested+0x60/0x4d0
[ 75.271558] [<ffffffff8126de2e>] kernfs_fop_open+0x16e/0x340
[ 75.278579] [<ffffffff811efaef>] do_dentry_open+0x1ff/0x350
[ 75.285510] [<ffffffff811efe11>] finish_open+0x31/0x40
[ 75.291948] [<ffffffff81202e26>] do_last+0xc16/0x1350
[ 75.298298] [<ffffffff8120362d>] path_openat+0xcd/0x640
[ 75.304821] [<ffffffff8120442d>] do_filp_open+0x4d/0xb0
[ 75.311353] [<ffffffff811f18a7>] do_sys_open+0x137/0x240
[ 75.317989] [<ffffffff811f19ce>] SyS_open+0x1e/0x20
[ 75.324122] [<ffffffff81672ca9>] system_call_fastpath+0x16/0x1b
[ 75.331437]
-> #0 (s_active#219){++++.+}:
[ 75.336174] [<ffffffff810cba76>] __lock_acquire+0x14e6/0x1b40
[ 75.343293] [<ffffffff810cc892>] lock_acquire+0xa2/0x120
[ 75.349923] [<ffffffff8126bc48>] __kernfs_remove+0x248/0x330
[ 75.356950] [<ffffffff8126ce55>] kernfs_remove_by_name_ns+0x45/0xa0
[ 75.364638] [<ffffffff8126f739>] remove_files.isra.1+0x39/0x70
[ 75.371850] [<ffffffff8126fa44>] sysfs_remove_group+0x44/0xa0
[ 75.378965] [<ffffffff814f280a>] cpufreq_governor_dbs+0x6da/0x770
[ 75.386478] [<ffffffff814f1277>] cs_cpufreq_governor_dbs+0x17/0x20
[ 75.394088] [<ffffffff814ed1bd>] __cpufreq_governor+0x11d/0x230
[ 75.401395] [<ffffffff814ed435>] cpufreq_set_policy+0x165/0x2c0
[ 75.408706] [<ffffffff814ee16d>] store_scaling_governor+0xad/0xf0
[ 75.416211] [<ffffffff814ecacc>] store+0x7c/0xc0
[ 75.422062] [<ffffffff8126e7e4>] sysfs_kf_write+0x44/0x60
[ 75.428790] [<ffffffff8126e0e7>] kernfs_fop_write+0xe7/0x170
[ 75.435806] [<ffffffff811f2857>] vfs_write+0xb7/0x1f0
[ 75.442146] [<ffffffff811f3488>] SyS_write+0x58/0xd0
[ 75.448390] [<ffffffff81672ca9>] system_call_fastpath+0x16/0x1b
[ 75.455706]
[ 75.455706] other info that might help us debug this:
[ 75.455706]
[ 75.464649] Possible unsafe locking scenario:
[ 75.464649]
[ 75.471265] CPU0 CPU1
[ 75.476327] ---- ----
[ 75.481385] lock(&policy->rwsem);
[ 75.485307] lock(s_active#219);
[ 75.491857] lock(&policy->rwsem);
[ 75.498592] lock(s_active#219);
[ 75.502331]
[ 75.502331] *** DEADLOCK ***
[ 75.502331]
[ 75.508948] 6 locks held by bash/3131:
[ 75.513136] #0: (sb_writers#3){.+.+.+}, at: [<ffffffff811f2953>]
vfs_write+0x1b3/0x1f0
[ 75.522259] #1: (&of->mutex){+.+.+.}, at: [<ffffffff8126e0bb>]
kernfs_fop_write+0xbb/0x170
[ 75.531751] #2: (s_active#221){.+.+.+}, at: [<ffffffff8126e0c3>]
kernfs_fop_write+0xc3/0x170
[ 75.541448] #3: (cpu_hotplug.lock){++++++}, at: [<ffffffff810752d4>]
get_online_cpus+0x24/0x70
[ 75.551339] #4: (cpufreq_rwsem){.+.+.+}, at: [<ffffffff814eca96>]
store+0x46/0xc0
[ 75.559957] #5: (&policy->rwsem){+++++.}, at: [<ffffffff814ecab0>]
store+0x60/0xc0
[ 75.568671]
[ 75.568671] stack backtrace:
[ 75.573544] CPU: 14 PID: 3131 Comm: bash Not tainted 3.16.0-rc7+ #22
[ 75.580647] Hardware name: Intel Corporation S2600CP/S2600CP, BIOS
RMLSDP.86I.R2.21.D636.1301031557 01/03/2013
[ 75.591824] 0000000000000000 000000000264b511 ffff881001837868 ffffffff816696a7
[ 75.600137] ffffffff8254dd40 ffff8810018378a8 ffffffff81662be3 ffff881001837900
[ 75.608451] ffff88100a6fba68 0000000000000005 ffff88100a6fba68 ffff88100a6fadc0
[ 75.616764] Call Trace:
[ 75.619505] [<ffffffff816696a7>] dump_stack+0x45/0x56
[ 75.625253] [<ffffffff81662be3>] print_circular_bug+0x1f9/0x207
[ 75.631966] [<ffffffff810cba76>] __lock_acquire+0x14e6/0x1b40
[ 75.638478] [<ffffffff810cb284>] ? __lock_acquire+0xcf4/0x1b40
[ 75.645095] [<ffffffff810c9f7a>] ? mark_held_locks+0x6a/0x90
[ 75.651522] [<ffffffff810cc892>] lock_acquire+0xa2/0x120
[ 75.657557] [<ffffffff8126ce55>] ? kernfs_remove_by_name_ns+0x45/0xa0
[ 75.664854] [<ffffffff8126bc48>] __kernfs_remove+0x248/0x330
[ 75.671279] [<ffffffff8126ce55>] ? kernfs_remove_by_name_ns+0x45/0xa0
[ 75.678577] [<ffffffff8126b117>] ? kernfs_name_hash+0x17/0xd0
[ 75.685097] [<ffffffff8126bdec>] ? kernfs_find_ns+0xbc/0x160
[ 75.691523] [<ffffffff8126ce55>] kernfs_remove_by_name_ns+0x45/0xa0
[ 75.698627] [<ffffffff8126f739>] remove_files.isra.1+0x39/0x70
[ 75.705242] [<ffffffff8126fa44>] sysfs_remove_group+0x44/0xa0
[ 75.711753] [<ffffffff814f280a>] cpufreq_governor_dbs+0x6da/0x770
[ 75.718661] [<ffffffff810ca0a5>] ? trace_hardirqs_on_caller+0x105/0x1d0
[ 75.726152] [<ffffffff810ca17d>] ? trace_hardirqs_on+0xd/0x10
[ 75.732672] [<ffffffff814f1277>] cs_cpufreq_governor_dbs+0x17/0x20
[ 75.739675] [<ffffffff814ed1bd>] __cpufreq_governor+0x11d/0x230
[ 75.746387] [<ffffffff814ed435>] cpufreq_set_policy+0x165/0x2c0
[ 75.753099] [<ffffffff814ee16d>] store_scaling_governor+0xad/0xf0
[ 75.760007] [<ffffffff814ed780>] ? cpufreq_update_policy+0x1f0/0x1f0
[ 75.767207] [<ffffffff814ecacc>] store+0x7c/0xc0
[ 75.772464] [<ffffffff8126e7e4>] sysfs_kf_write+0x44/0x60
[ 75.778586] [<ffffffff8126e0e7>] kernfs_fop_write+0xe7/0x170
[ 75.785000] [<ffffffff811f2857>] vfs_write+0xb7/0x1f0
[ 75.790741] [<ffffffff811f3488>] SyS_write+0x58/0xd0
[ 75.796386] [<ffffffff81672ca9>] system_call_fastpath+0x16/0x1b
[ 75.803172] cpufreq_set_policy: starting governor ondemand
[ 75.809341] cpufreq_governor_dbs: creating sysfs files for governor ondemand

P.
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