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    Subject[PATCH 3.16 317/357] cpufreq: release policy->rwsem on error
    Date
    3.16-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Prarit Bhargava <prarit@redhat.com>

    commit 7106e02baed4a72fb23de56b02ad4d31daa74d95 upstream.

    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

    Fixes: 4e97b631f24c (cpufreq: Initialize governor for a new policy under policy->rwsem)
    Signed-off-by: Prarit Bhargava <prarit@redhat.com>
    Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/cpufreq/cpufreq.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/drivers/cpufreq/cpufreq.c
    +++ b/drivers/cpufreq/cpufreq.c
    @@ -1279,6 +1279,8 @@ 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:



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