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Date: Mon, 22 Sep 2014 16:06:17 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Viresh Kumar <viresh.kumar@...aro.org>,
Prarit Bhargava <prarit@...hat.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] cpufreq, release policy->rwsem on error
On Thursday, September 11, 2014 10:05:43 AM Viresh Kumar wrote:
> On 10 September 2014 19:42, Prarit Bhargava <prarit@...hat.com> wrote:
> > I have not been able to reliably reproduce the hardware failure that caused
> > the warning. In order to reproduce this I resorted to (sorry for the
> > cut-and-paste)
> >
> > diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c
> > index 728a2d8..c7724d2 100644
> > --- a/drivers/cpufreq/pcc-cpufreq.c
> > +++ b/drivers/cpufreq/pcc-cpufreq.c
> > @@ -146,6 +146,8 @@ static unsigned int pcc_get_freq(unsigned int cpu)
> > u32 input_buffer;
> > u32 output_buffer;
> >
> > + return 0;
> > +
> > spin_lock(&pcc_lock);
> >
> > pr_debug("get: get_freq for CPU %d\n", cpu);
> >
> > to simulate the cpufreq_driver->get() hardware failure.
> >
> > ---8<---
> >
> > While debugging a cpufreq-related hardware failure on a system I saw the
> > following lockdep warning:
> >
> > =========================
> > [ BUG: held lock freed! ] 3.17.0-rc4+ #1 Tainted: G E
> > -------------------------
> > insmod/2247 is freeing memory ffff88006e1b1400-ffff88006e1b17ff, with a lock still held there!
> > (&policy->rwsem){+.+...}, at: [<ffffffff8156d37d>] __cpufreq_add_dev.isra.21+0x47d/0xb80
> > 3 locks held by insmod/2247:
> > #0: (subsys mutex#5){+.+.+.}, at: [<ffffffff81485579>] subsys_interface_register+0x69/0x120
> > #1: (cpufreq_rwsem){.+.+.+}, at: [<ffffffff8156cf73>] __cpufreq_add_dev.isra.21+0x73/0xb80
> > #2: (&policy->rwsem){+.+...}, at: [<ffffffff8156d37d>] __cpufreq_add_dev.isra.21+0x47d/0xb80
> >
> > stack backtrace:
> > CPU: 0 PID: 2247 Comm: insmod Tainted: G E 3.17.0-rc4+ #1
> > Hardware name: HP ProLiant MicroServer Gen8, BIOS J06 08/24/2013
> > 0000000000000000 000000008f3063c4 ffff88006f87bb30 ffffffff8171b358
> > ffff88006bcf3750 ffff88006f87bb68 ffffffff810e09e1 ffff88006e1b1400
> > ffffea0001b86c00 ffffffff8156d327 ffff880073003500 0000000000000246
> > Call Trace:
> > [<ffffffff8171b358>] dump_stack+0x4d/0x66
> > [<ffffffff810e09e1>] debug_check_no_locks_freed+0x171/0x180
> > [<ffffffff8156d327>] ? __cpufreq_add_dev.isra.21+0x427/0xb80
> > [<ffffffff8121412b>] kfree+0xab/0x2b0
> > [<ffffffff8156d327>] __cpufreq_add_dev.isra.21+0x427/0xb80
> > [<ffffffff81724cf7>] ? _raw_spin_unlock+0x27/0x40
> > [<ffffffffa003517f>] ? pcc_cpufreq_do_osc+0x17f/0x17f [pcc_cpufreq]
> > [<ffffffff8156da8e>] cpufreq_add_dev+0xe/0x10
> > [<ffffffff814855d1>] subsys_interface_register+0xc1/0x120
> > [<ffffffff8156bcf2>] cpufreq_register_driver+0x112/0x340
> > [<ffffffff8121415a>] ? kfree+0xda/0x2b0
> > [<ffffffffa003517f>] ? pcc_cpufreq_do_osc+0x17f/0x17f [pcc_cpufreq]
> > [<ffffffffa003562e>] pcc_cpufreq_init+0x4af/0xe81 [pcc_cpufreq]
> > [<ffffffffa003517f>] ? pcc_cpufreq_do_osc+0x17f/0x17f [pcc_cpufreq]
> > [<ffffffff81002144>] do_one_initcall+0xd4/0x210
> > [<ffffffff811f7472>] ? __vunmap+0xd2/0x120
> > [<ffffffff81127155>] load_module+0x1315/0x1b70
> > [<ffffffff811222a0>] ? store_uevent+0x70/0x70
> > [<ffffffff811229d9>] ? copy_module_from_fd.isra.44+0x129/0x180
> > [<ffffffff81127b86>] SyS_finit_module+0xa6/0xd0
> > [<ffffffff81725b69>] system_call_fastpath+0x16/0x1b
> > cpufreq: __cpufreq_add_dev: ->get() failed
> > insmod: ERROR: could not insert module pcc-cpufreq.ko: No such device
> >
> > The warning occurs in the __cpufreq_add_dev() code which does
> >
> > down_write(&policy->rwsem);
> > ...
> > if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
> > policy->cur = cpufreq_driver->get(policy->cpu);
> > if (!policy->cur) {
> > pr_err("%s: ->get() failed\n", __func__);
> > goto err_get_freq;
> > }
> >
> > If cpufreq_driver->get(policy->cpu) returns an error we execute the
> > code at err_get_freq, which does not up the policy->rwsem. This causes
> > the lockdep warning.
> >
> > Trivial patch to up the policy->rwsem in the error path.
> >
> > After the patch has been applied, and an error occurs in the
> > cpufreq_driver->get(policy->cpu) call we will now see
> >
> > cpufreq: __cpufreq_add_dev: ->get() failed
> > cpufreq: __cpufreq_add_dev: ->get() failed
> > modprobe: ERROR: could not insert 'pcc_cpufreq': No such device
> >
> > Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Cc: Viresh Kumar <viresh.kumar@...aro.org>
> > Cc: linux-pm@...r.kernel.org
> > ---
> > drivers/cpufreq/cpufreq.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index d9fdedd..aadaed0 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -1289,6 +1289,8 @@ err_get_freq:
> > per_cpu(cpufreq_cpu_data, j) = NULL;
> > write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >
> > + up_write(&policy->rwsem);
> > +
> > if (cpufreq_driver->exit)
> > cpufreq_driver->exit(policy);
> > err_set_policy_cpu:
Queued up for 3.17-rc7, thanks!
> Fixes: "4e97b63 cpufreq: Initialize governor for a new policy under
> policy->rwsem"
> Stable: 3.14+
And thanks for the info above.
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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