linux-kernel - Re: [PATCH] pinctrl: core: Make p->state in order in pinctrl_commit

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Message-ID: <761f322c-47bb-1233-ffd2-f6c13bcd2466@quicinc.com>
Date:   Wed, 2 Nov 2022 09:26:22 +0800
From:   "Aiqun(Maria) Yu" <quic_aiquny@...cinc.com>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
CC:     <linus.walleij@...aro.org>, <linux-gpio@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: core: Make p->state in order in
 pinctrl_commit_state

Hi Pavan,

On 11/1/2022 12:30 PM, Pavan Kondeti wrote:
> Hi Maria,
> 
> On Thu, Oct 27, 2022 at 02:54:08PM +0800, Maria Yu wrote:
>> We've got a dump that current cpu is in pinctrl_commit_state, the
>> old_state != p->state while the stack is still in the process of
>> pinmux_disable_setting. So it means even if the current p->state is
>> changed in new state, the settings are not yet up-to-date enabled
>> complete yet.
>>
>> Currently p->state in different value to synchronize the
>> pinctrl_commit_state behaviors. The p->state will have transaction like
>> old_state -> NULL -> new_state. When in old_state, it will try to
>> disable all the all state settings. And when after new state settings
>> enabled, p->state will changed to the new state after that. So use
>> smp_mb to synchronize the p->state variable and the settings in order.
>> ---
>>   drivers/pinctrl/core.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/pinctrl/core.c b/drivers/pinctrl/core.c
>> index 9e57f4c62e60..cd917a5b1a0a 100644
>> --- a/drivers/pinctrl/core.c
>> +++ b/drivers/pinctrl/core.c
>> @@ -1256,6 +1256,7 @@ static int pinctrl_commit_state(struct pinctrl *p, struct pinctrl_state *state)
>>   		}
>>   	}
>>   
>> +	smp_mb();
>>   	p->state = NULL;
>>   
>>   	/* Apply all the settings for the new state - pinmux first */
>> @@ -1305,6 +1306,7 @@ static int pinctrl_commit_state(struct pinctrl *p, struct pinctrl_state *state)
>>   			pinctrl_link_add(setting->pctldev, p->dev);
>>   	}
>>   
>> +	smp_mb();
>>   	p->state = state;
>>   
> 
>  From your commit description, are you inferring that this p->state assignment
> re-ordered wrt pinmux_disable_setting()? btw, I don't see any locking that
> protects concurrent access to p->state modifications. For whatever reasons, if
> a client makes concurrent calls to pinctrl_select_state(), we can land up in
> the situation, you are seeing. correct?
correct.
> 
> Thanks,
> Pavan
> 


-- 
Thx and BRs,
Aiqun(Maria) Yu