linux-kernel - Re: [PATCH] drm/amdgpu: off by on in amdgpu_device_attr_create

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Date:   Wed, 20 May 2020 15:52:09 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     christian.koenig@....com
Cc:     Alex Deucher <alexander.deucher@....com>,
        Kevin Wang <kevin1.wang@....com>,
        David Airlie <airlied@...ux.ie>,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org,
        Hawking Zhang <Hawking.Zhang@....com>,
        Rui Huang <ray.huang@....com>, dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel@...ll.ch>, Evan Quan <evan.quan@....com>,
        Kenneth Feng <kenneth.feng@....com>,
        Yintian Tao <yttao@....com>
Subject: Re: [PATCH] drm/amdgpu: off by on in
 amdgpu_device_attr_create_groups() error handling

On Wed, May 20, 2020 at 02:05:19PM +0200, Christian König wrote:
> Am 20.05.20 um 14:00 schrieb Dan Carpenter:
> > This loop in the error handling code should start a "i - 1" and end at
> > "i == 0".  Currently it starts a "i" and ends at "i == 1".  The result
> > is that it removes one attribute that wasn't created yet, and leaks the
> > zeroeth attribute.
> > 
> > Fixes: 4e01847c38f7 ("drm/amdgpu: optimize amdgpu device attribute code")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c | 5 ++---
> >   1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
> > index b75362bf0742..ee4a8e44fbeb 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
> > @@ -1931,7 +1931,7 @@ static int amdgpu_device_attr_create_groups(struct amdgpu_device *adev,
> >   					    uint32_t mask)
> >   {
> >   	int ret = 0;
> > -	uint32_t i = 0;
> > +	int i;
> >   	for (i = 0; i < counts; i++) {
> >   		ret = amdgpu_device_attr_create(adev, &attrs[i], mask);
> > @@ -1942,9 +1942,8 @@ static int amdgpu_device_attr_create_groups(struct amdgpu_device *adev,
> >   	return 0;
> >   failed:
> > -	for (; i > 0; i--) {
> > +	while (--i >= 0)
> 
> As far as I know the common idiom for this is while (i--) which even works
> without changing the type of i to signed.

It's about 50/50, one way or the other.  To me --i >= 0 seems far more
readable.

I've been trying to figure out which tool tells people to make iterators
unsigned so I can help them avoid it.  :/  I understand how in theory
iterators could go above INT_MAX but if we're going above INT_MAX then
probably we should use a 64 bit type.  There are very few times where 2
billion iterations is not enough but in those situations probably 4
billion is not enough either.  So unsigned int iterators never or seldom
solve real life bugs but they regularly cause them.

regards,
dan carpenter