linux-kernel - Re: [PATCH] device: fix missing check on list iterator

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Date:   Sun, 27 Mar 2022 07:22:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     airlied@...ux.ie, bskeggs@...hat.com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, kherbst@...hat.com,
        linux-kernel@...r.kernel.org, lyude@...hat.com,
        nouveau@...ts.freedesktop.org, stable@...r.kernel.org
Subject: Re: [PATCH] device: fix missing check on list iterator

On 3/26/22 23:59, Xiaomeng Tong wrote:
> On Sat, 26 Mar 2022 22:38:05 -0700, Guenter Roeck <linux@...ck-us.net> wrote:
>>> @@ -103,11 +103,16 @@ nvkm_control_mthd_pstate_attr(struct nvkm_control *ctrl, void *data, u32 size)
>>>    		return -EINVAL;
>>>    
>>>    	if (args->v0.state != NVIF_CONTROL_PSTATE_ATTR_V0_STATE_CURRENT) {
>>> -		list_for_each_entry(pstate, &clk->states, head) {
>>> -			if (i++ == args->v0.state)
>>> +		list_for_each_entry(iter, &clk->states, head) {
>>> +			if (i++ == args->v0.state) {
>>> +				pstate = iter;
>>
>> Is iter and the assignment really necessary ? Unless I am missing something,
>> list_for_each_entry() always assigns pos (pstate/iter), even if the list is
>> empty. If nothing is found, pstate would be NULL at the end, so
> 
> the pstate will not be NULL at the end! so the assignment is necessary!
> #define list_for_each_entry(pos, head, member)                          \
>      for (pos = __container_of((head)->next, pos, member);               \
>           &pos->member != (head);                                        \
>           pos = __container_of(pos->member.next, pos, member))
> 


Uuh, yes, you are correct. Sorry for the noise.

Guenter