Re: [cpufreq] swapper/1 is trying to release lock cpufreq_rwsem at cpufreq_add_dev()

From: Viresh Kumar
Date: Tue Aug 20 2013 - 11:46:58 EST

On 20 August 2013 21:04, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
> Greetings,
>
> I got the below dmesg and the first bad commit is
>
> commit 6eed9404ab3c4baea54ce4c7e862e69df1d39f38
> Author: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> Date: Tue Aug 6 22:53:11 2013 +0530
>
> cpufreq: Use rwsem for protecting critical sections
>
> Critical sections of the cpufreq core are protected with the help of
> the driver module owner's refcount, which isn't the correct approach,
> because it causes rmmod to return an error when some routine has
> updated that refcount.
>
> Let's use rwsem for this purpose instead. Only
> cpufreq_unregister_driver() will use write sem
> and everybody else will use read sem.
>
> [rjw: Subject & changelog]
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Somebody reported similar stuff with a fix but sent it to wrong
mailing list. Can you
try attached patch?

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Subject: [RFC PATCH next]cpufreq: fix bad unlock balance on !CONFIG_SMP
From: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
To: linux-next list <linux-next@xxxxxxxxxxxxxxx>
Cc: viresh.kumar@xxxxxxxxxx, rafael.j.wysocki@xxxxxxxxx
Date: Tue, 20 Aug 2013 13:11:50 +0800
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This patch tries to fix lockdep complaint attached below.

It seems that we should always read acquire the cpufreq_rwsem, whether
CONFIG_SMP is enabled or not. And CONFIG_HOTPLUG_CPU depends on
CONFIG_SMP, so it seems we don't need CONFIG_SMP for the code enabled by
CONFIG_HOTPLUG_CPU.

[ 0.504191] =====================================
[ 0.504627] [ BUG: bad unlock balance detected! ]
[ 0.504627] 3.11.0-rc6-next-20130819 #1 Not tainted
[ 0.504627] -------------------------------------
[ 0.504627] swapper/1 is trying to release lock (cpufreq_rwsem) at:
[ 0.504627] [<ffffffff813d927a>] cpufreq_add_dev+0x13a/0x3e0
[ 0.504627] but there are no more locks to release!
[ 0.504627]
[ 0.504627] other info that might help us debug this:
[ 0.504627] 1 lock held by swapper/1:
[ 0.504627] #0: (subsys mutex#4){+.+.+.}, at: [<ffffffff8134a7bf>] subsys_interface_register+0x4f/0xe0
[ 0.504627]
[ 0.504627] stack backtrace:
[ 0.504627] CPU: 0 PID: 1 Comm: swapper Not tainted 3.11.0-rc6-next-20130819 #1
[ 0.504627] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
[ 0.504627] ffffffff813d927a ffff88007f847c98 ffffffff814c062b ffff88007f847cc8
[ 0.504627] ffffffff81098bce ffff88007f847cf8 ffffffff81aadc30 ffffffff813d927a
[ 0.504627] 00000000ffffffff ffff88007f847d68 ffffffff8109d0be 0000000000000006
[ 0.504627] Call Trace:
[ 0.504627] [<ffffffff813d927a>] ? cpufreq_add_dev+0x13a/0x3e0
[ 0.504627] [<ffffffff814c062b>] dump_stack+0x19/0x1b
[ 0.504627] [<ffffffff81098bce>] print_unlock_imbalance_bug+0xfe/0x110
[ 0.504627] [<ffffffff813d927a>] ? cpufreq_add_dev+0x13a/0x3e0
[ 0.504627] [<ffffffff8109d0be>] lock_release_non_nested+0x1ee/0x310
[ 0.504627] [<ffffffff81099d0e>] ? mark_held_locks+0xae/0x120
[ 0.504627] [<ffffffff811510cb>] ? kfree+0xcb/0x1d0
[ 0.504627] [<ffffffff813d77ea>] ? cpufreq_policy_free+0x4a/0x60
[ 0.504627] [<ffffffff813d927a>] ? cpufreq_add_dev+0x13a/0x3e0
[ 0.504627] [<ffffffff8109d2a4>] lock_release+0xc4/0x250
[ 0.504627] [<ffffffff8106c9f3>] up_read+0x23/0x40
[ 0.504627] [<ffffffff813d927a>] cpufreq_add_dev+0x13a/0x3e0
[ 0.504627] [<ffffffff8134a809>] subsys_interface_register+0x99/0xe0
[ 0.504627] [<ffffffff81b19f3b>] ? cpufreq_gov_dbs_init+0x12/0x12
[ 0.504627] [<ffffffff813d7f0d>] cpufreq_register_driver+0x9d/0x1d0
[ 0.504627] [<ffffffff81b19f3b>] ? cpufreq_gov_dbs_init+0x12/0x12
[ 0.504627] [<ffffffff81b1a039>] acpi_cpufreq_init+0xfe/0x1f8
[ 0.504627] [<ffffffff810002ba>] do_one_initcall+0xda/0x180
[ 0.504627] [<ffffffff81ae301e>] kernel_init_freeable+0x12c/0x1bb
[ 0.504627] [<ffffffff81ae2841>] ? do_early_param+0x8c/0x8c
[ 0.504627] [<ffffffff814b4dd0>] ? rest_init+0x140/0x140
[ 0.504627] [<ffffffff814b4dde>] kernel_init+0xe/0xf0
[ 0.504627] [<ffffffff814d029a>] ret_from_fork+0x7a/0xb0
[ 0.504627] [<ffffffff814b4dd0>] ? rest_init+0x140/0x140

Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
---
drivers/cpufreq/cpufreq.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index c0ef84d..8408957 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -986,6 +986,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
cpufreq_cpu_put(policy);
return 0;
}
+#endif

if (!down_read_trylock(&cpufreq_rwsem))
return 0;
@@ -1004,7 +1005,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif,
}
read_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif
-#endif

if (frozen)
/* Restore the saved policy when doing light-weight init */