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

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Message-Id: <20220327065950.7886-1-xiam0nd.tong@gmail.com>
Date:   Sun, 27 Mar 2022 14:59:50 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     linux@...ck-us.net
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,
        xiam0nd.tong@...il.com
Subject: Re: [PATCH] device: fix missing check on list iterator

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))

--
Xiaomeng Tong