On 15/10/2018 14:52, Dmitry Osipenko wrote:
> On 10/15/18 3:52 PM, Jon Hunter wrote:
>>
>> On 30/08/18 19:36, Dmitry Osipenko wrote:
>>> This fixes splats like the one below if CONFIG_DEBUG_ATOMIC_SLEEP=y
>>> and machine (Tegra30) booted with SMP=n or all secondary CPU's are put
>>> offline.
>>>
>>>  BUG: sleeping function called from invalid context at 
>>> kernel/locking/mutex.c:254
>>>  in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/0
>>>  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G         C        
>>> 4.18.0-next-20180821-00180-gc3ebb6544e44-dirty #823
>>>  Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
>>>  [<c01134f4>] (unwind_backtrace) from [<c010db2c>] (show_stack+0x20/0x24)
>>>  [<c010db2c>] (show_stack) from [<c0bd0f3c>] (dump_stack+0x94/0xa8)
>>>  [<c0bd0f3c>] (dump_stack) from [<c0151df8>] (___might_sleep+0x13c/0x174)
>>>  [<c0151df8>] (___might_sleep) from [<c0151ea0>] (__might_sleep+0x70/0xa8)
>>>  [<c0151ea0>] (__might_sleep) from [<c0bec2b8>] (mutex_lock+0x2c/0x70)
>>>  [<c0bec2b8>] (mutex_lock) from [<c0589844>] 
>>> (tegra_powergate_is_powered+0x44/0xa8)
>>>  [<c0589844>] (tegra_powergate_is_powered) from [<c0581a60>] 
>>> (tegra30_cpu_rail_off_ready+0x30/0x74)
>>>  [<c0581a60>] (tegra30_cpu_rail_off_ready) from [<c0122244>] 
>>> (tegra30_idle_lp2+0xa0/0x108)
>>>  [<c0122244>] (tegra30_idle_lp2) from [<c0853438>] 
>>> (cpuidle_enter_state+0x140/0x540)
>>>  [<c0853438>] (cpuidle_enter_state) from [<c08538a4>] 
>>> (cpuidle_enter+0x40/0x4c)
>>>  [<c08538a4>] (cpuidle_enter) from [<c01595e0>] (call_cpuidle+0x30/0x48)
>>>  [<c01595e0>] (call_cpuidle) from [<c01599f8>] (do_idle+0x238/0x28c)
>>>  [<c01599f8>] (do_idle) from [<c0159d28>] (cpu_startup_entry+0x28/0x2c)
>>>  [<c0159d28>] (cpu_startup_entry) from [<c0be76c8>] (rest_init+0xd8/0xdc)
>>>  [<c0be76c8>] (rest_init) from [<c1200f50>] (start_kernel+0x41c/0x430)
>>
>> Given the above, rather than converting to a spinlock I wonder if we are
>> just better off dropping the mutex completely from
>> tegra_powergate_is_powered()? Otherwise ...
>>
>>> Signed-off-by: Dmitry Osipenko <dig...@gmail.com>
>>> ---
>>>  drivers/soc/tegra/pmc.c | 36 ++++++++++++++++++------------------
>>>  1 file changed, 18 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>>> index 2d6f3fcf3211..d6bc9f66f1cd 100644
>>> --- a/drivers/soc/tegra/pmc.c
>>> +++ b/drivers/soc/tegra/pmc.c
>>> @@ -186,7 +186,7 @@ struct tegra_pmc_soc {
>>>   * @lp0_vec_phys: physical base address of the LP0 warm boot code
>>>   * @lp0_vec_size: size of the LP0 warm boot code
>>>   * @powergates_available: Bitmap of available power gates
>>> - * @powergates_lock: mutex for power gate register access
>>> + * @powergates_lock: lock for power gate register access
>>>   */
>>>  struct tegra_pmc {
>>>     struct device *dev;
>>> @@ -215,7 +215,7 @@ struct tegra_pmc {
>>>     u32 lp0_vec_size;
>>>     DECLARE_BITMAP(powergates_available, TEGRA_POWERGATE_MAX);
>>>  
>>> -   struct mutex powergates_lock;
>>> +   spinlock_t powergates_lock;
>>>  };
>>>  
>>>  static struct tegra_pmc *pmc = &(struct tegra_pmc) {
>>> @@ -288,10 +288,10 @@ static int tegra_powergate_set(unsigned int id, bool 
>>> new_state)
>>>     if (id == TEGRA_POWERGATE_3D && pmc->soc->has_gpu_clamps)
>>>             return -EINVAL;
>>>  
>>> -   mutex_lock(&pmc->powergates_lock);
>>> +   spin_lock(&pmc->powergates_lock);
>>>  
>>>     if (tegra_powergate_state(id) == new_state) {
>>> -           mutex_unlock(&pmc->powergates_lock);
>>> +           spin_unlock(&pmc->powergates_lock);
>>>             return 0;
>>>     }
>>>  
>>> @@ -300,7 +300,7 @@ static int tegra_powergate_set(unsigned int id, bool 
>>> new_state)
>>>     err = readx_poll_timeout(tegra_powergate_state, id, status,
>>>                              status == new_state, 10, 100000);
>>>  
>>> -   mutex_unlock(&pmc->powergates_lock);
>>> +   spin_unlock(&pmc->powergates_lock);
>>
>> ... the above readx_poll_timeout needs to be converted to the atomic
>> version. Furthermore, the above 100ms timeout is probably not suited to
>> spinlock.
> 
> It's converted in the second patch. Seems mutex indeed could be dropped from 
> tegra_powergate_is_powered, at least for now I can't recall why decided to 
> keep the locking. Thank you for the review, I'll try to drop the mutex and 
> come back with v2 if it will be fine.

Sorry if you were waiting for my response, but yes sounds good to me.

Cheers
Jon

-- 
nvpublic

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