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    Subject[PATCH 5.4 50/50] PM / devfreq: Add missing locking while setting suspend_freq
    Date
    From: Marek Szyprowski <m.szyprowski@samsung.com>

    commit e1e047ace8cef6d143f38c7d769753f133becbe6 upstream.

    Commit 2abb0d5268ae ("PM / devfreq: Lock devfreq in trans_stat_show")
    revealed a missing locking while calling devfreq_update_status() function
    during suspend/resume cycle.

    Code analysis revealed that devfreq_set_target() function was called
    without needed locks held for setting device specific suspend_freq if such
    has been defined. This patch fixes that by adding the needed locking, what
    fixes following kernel warning on Exynos4412-based OdroidU3 board during
    system suspend:

    PM: suspend entry (deep)
    Filesystems sync: 0.002 seconds
    Freezing user space processes ... (elapsed 0.001 seconds) done.
    OOM killer disabled.
    Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
    ------------[ cut here ]------------
    WARNING: CPU: 2 PID: 1385 at drivers/devfreq/devfreq.c:204 devfreq_update_status+0xc0/0x188
    Modules linked in:
    CPU: 2 PID: 1385 Comm: rtcwake Not tainted 5.4.0-rc6-next-20191111 #6848
    Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
    [<c0112588>] (unwind_backtrace) from [<c010e070>] (show_stack+0x10/0x14)
    [<c010e070>] (show_stack) from [<c0afb010>] (dump_stack+0xb4/0xe0)
    [<c0afb010>] (dump_stack) from [<c01272e0>] (__warn+0xf4/0x10c)
    [<c01272e0>] (__warn) from [<c01273a8>] (warn_slowpath_fmt+0xb0/0xb8)
    [<c01273a8>] (warn_slowpath_fmt) from [<c07d105c>] (devfreq_update_status+0xc0/0x188)
    [<c07d105c>] (devfreq_update_status) from [<c07d2d70>] (devfreq_set_target+0xb0/0x15c)
    [<c07d2d70>] (devfreq_set_target) from [<c07d3598>] (devfreq_suspend+0x2c/0x64)
    [<c07d3598>] (devfreq_suspend) from [<c05de0b0>] (dpm_suspend+0xa4/0x57c)
    [<c05de0b0>] (dpm_suspend) from [<c05def74>] (dpm_suspend_start+0x98/0xa0)
    [<c05def74>] (dpm_suspend_start) from [<c0195b58>] (suspend_devices_and_enter+0xec/0xc74)
    [<c0195b58>] (suspend_devices_and_enter) from [<c0196a20>] (pm_suspend+0x340/0x410)
    [<c0196a20>] (pm_suspend) from [<c019480c>] (state_store+0x6c/0xc8)
    [<c019480c>] (state_store) from [<c033fc50>] (kernfs_fop_write+0x10c/0x228)
    [<c033fc50>] (kernfs_fop_write) from [<c02a6d3c>] (__vfs_write+0x30/0x1d0)
    [<c02a6d3c>] (__vfs_write) from [<c02a9afc>] (vfs_write+0xa4/0x180)
    [<c02a9afc>] (vfs_write) from [<c02a9d58>] (ksys_write+0x60/0xd8)
    [<c02a9d58>] (ksys_write) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
    Exception stack(0xed3d7fa8 to 0xed3d7ff0)
    ...
    irq event stamp: 9667
    hardirqs last enabled at (9679): [<c0b1e7c4>] _raw_spin_unlock_irq+0x20/0x58
    hardirqs last disabled at (9698): [<c0b16a20>] __schedule+0xd8/0x818
    softirqs last enabled at (9694): [<c01026fc>] __do_softirq+0x4fc/0x5fc
    softirqs last disabled at (9719): [<c012fe68>] irq_exit+0x16c/0x170
    ---[ end trace 41ac5b57d046bdbc ]---
    ------------[ cut here ]------------

    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/devfreq/devfreq.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/drivers/devfreq/devfreq.c
    +++ b/drivers/devfreq/devfreq.c
    @@ -902,7 +902,9 @@ int devfreq_suspend_device(struct devfre
    }

    if (devfreq->suspend_freq) {
    + mutex_lock(&devfreq->lock);
    ret = devfreq_set_target(devfreq, devfreq->suspend_freq, 0);
    + mutex_unlock(&devfreq->lock);
    if (ret)
    return ret;
    }
    @@ -930,7 +932,9 @@ int devfreq_resume_device(struct devfreq
    return 0;

    if (devfreq->resume_freq) {
    + mutex_lock(&devfreq->lock);
    ret = devfreq_set_target(devfreq, devfreq->resume_freq, 0);
    + mutex_unlock(&devfreq->lock);
    if (ret)
    return ret;
    }

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