linux-kernel - RE: [PATCH v2] gpu: drm/amd: Remove the redundant null pointer check in list_for_each

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Message-ID: <CY8PR12MB743557DB910470B5433B320D8554A@CY8PR12MB7435.namprd12.prod.outlook.com>
Date:   Mon, 12 Jun 2023 15:39:38 +0000
From:   "Kim, Jonathan" <Jonathan.Kim@....com>
To:     "Kuehling, Felix" <Felix.Kuehling@....com>,
        Lu Hongfei <luhongfei@...o.com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:AMD KFD" <amd-gfx@...ts.freedesktop.org>,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
CC:     "opensource.kernel@...o.com" <opensource.kernel@...o.com>
Subject: RE: [PATCH v2] gpu: drm/amd: Remove the redundant null pointer check
 in list_for_each_entry() loops

[Public]

> -----Original Message-----
> From: Kuehling, Felix <Felix.Kuehling@....com>
> Sent: Monday, June 12, 2023 11:25 AM
> To: Lu Hongfei <luhongfei@...o.com>; Deucher, Alexander
> <Alexander.Deucher@....com>; Koenig, Christian
> <Christian.Koenig@....com>; Pan, Xinhui <Xinhui.Pan@....com>; David
> Airlie <airlied@...il.com>; Daniel Vetter <daniel@...ll.ch>; open list:AMD
> KFD <amd-gfx@...ts.freedesktop.org>; open list:DRM DRIVERS <dri-
> devel@...ts.freedesktop.org>; open list <linux-kernel@...r.kernel.org>; Kim,
> Jonathan <Jonathan.Kim@....com>
> Cc: opensource.kernel@...o.com
> Subject: Re: [PATCH v2] gpu: drm/amd: Remove the redundant null pointer
> check in list_for_each_entry() loops
>
> [+Jon]
>
> Am 2023-06-12 um 07:58 schrieb Lu Hongfei:
> > pqn bound in list_for_each_entry loop will not be null, so there is
> > no need to check whether pqn is NULL or not.
> > Thus remove a redundant null pointer check.
> >
> > Signed-off-by: Lu Hongfei <luhongfei@...o.com>
> > ---
> > The filename of the previous version was:
> > 0001-gpu-drm-amd-Fix-the-bug-in-list_for_each_entry-loops.patch
> >
> > The modifications made compared to the previous version are as follows:
> > 1. Modified the patch title
> > 2. "Thus remove a redundant null pointer check." is used instead of
> >     "We could remove this check."
> >
> >   drivers/gpu/drm/amd/amdkfd/kfd_debug.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_debug.c
> b/drivers/gpu/drm/amd/amdkfd/kfd_debug.c
> > index cd34e7aaead4..10d0cef844f0 100644
> > --- a/drivers/gpu/drm/amd/amdkfd/kfd_debug.c
> > +++ b/drivers/gpu/drm/amd/amdkfd/kfd_debug.c
> > @@ -1097,9 +1097,6 @@ void
> kfd_dbg_set_enabled_debug_exception_mask(struct kfd_process *target,
> >
> >     pqm = &target->pqm;
> >     list_for_each_entry(pqn, &pqm->queues, process_queue_list) {
> > -           if (!pqn)
>
> Right, this check doesn't make a lot of sense. Jon, was this meant to
> check pqn->q?

Yes that's a bug.  It should be a null check on the queue itself.
I'll send out the fix shortly.

Thanks,

Jon

>
> Regards,
>    Felix
>
>
> > -                   continue;
> > -
> >             found_mask |= pqn->q->properties.exception_status;
> >     }
> >