netdev - Re: [PATCH net] net/mlx5: Don't fail driver on failure to create debugfs

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Date:   Thu, 11 Jun 2020 21:58:40 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "natechancellor@...il.com" <natechancellor@...il.com>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Leon Romanovsky <leonro@...lanox.com>,
        Vu Pham <vuhuong@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "leon@...nel.org" <leon@...nel.org>
Subject: Re: [PATCH net] net/mlx5: Don't fail driver on failure to create
 debugfs

On Mon, 2020-06-08 at 14:22 -0700, Nathan Chancellor wrote:
> On Thu, Jun 04, 2020 at 04:44:00AM +0000, Saeed Mahameed wrote:
> > On Wed, 2020-06-03 at 11:34 -0700, Nathan Chancellor wrote:
> > > On Tue, Jun 02, 2020 at 12:27:24PM -0700, Nathan Chancellor
> > > wrote:
> > > > On Tue, Jun 02, 2020 at 03:28:37PM +0300, Leon Romanovsky
> > > > wrote:
> > > > > From: Leon Romanovsky <leonro@...lanox.com>
> > > > > 
> > > > > Clang warns:
> > > > > 
> > > > > drivers/net/ethernet/mellanox/mlx5/core/main.c:1278:6:
> > > > > warning:
> > > > > variable
> > > > > 'err' is used uninitialized whenever 'if' condition is true
> > > > > [-Wsometimes-uninitialized]
> > > > >         if (!priv->dbg_root) {
> > > > >             ^~~~~~~~~~~~~~~
> > > > > drivers/net/ethernet/mellanox/mlx5/core/main.c:1303:9: note:
> > > > > uninitialized use occurs here
> > > > >         return err;
> > > > >                ^~~
> > > > > drivers/net/ethernet/mellanox/mlx5/core/main.c:1278:2: note:
> > > > > remove the
> > > > > 'if' if its condition is always false
> > > > >         if (!priv->dbg_root) {
> > > > >         ^~~~~~~~~~~~~~~~~~~~~~
> > > > > drivers/net/ethernet/mellanox/mlx5/core/main.c:1259:9: note:
> > > > > initialize
> > > > > the variable 'err' to silence this warning
> > > > >         int err;
> > > > >                ^
> > > > >                 = 0
> > > > > 1 warning generated.
> > > > > 
> > > > > The check of returned value of debugfs_create_dir() is wrong
> > > > > because
> > > > > by the design debugfs failures should never fail the driver
> > > > > and
> > > > > the
> > > > > check itself was wrong too. The kernel compiled without
> > > > > CONFIG_DEBUG_FS
> > > > > will return ERR_PTR(-ENODEV) and not NULL as expected.
> > > > > 
> > > > > Fixes: 11f3b84d7068 ("net/mlx5: Split mdev init and pci
> > > > > init")
> > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1042
> > > > > Reported-by: Nathan Chancellor <natechancellor@...il.com>
> > > > > Signed-off-by: Leon Romanovsky <leonro@...lanox.com>
> > > > 
> > > > Thanks! That's what I figured it should be.
> > > > 
> > > > Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> > > > 
> > > > > ---
> > > > > Original discussion:
> > > > > https://lore.kernel.org/lkml/20200530055447.1028004-1-natechancellor@gmail.com
> > > > > ---
> > > > >  drivers/net/ethernet/mellanox/mlx5/core/main.c | 5 -----
> > > > >  1 file changed, 5 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/main.c
> > > > > b/drivers/net/ethernet/mellanox/mlx5/core/main.c
> > > > > index df46b1fce3a7..110e8d277d15 100644
> > > > > --- a/drivers/net/ethernet/mellanox/mlx5/core/main.c
> > > > > +++ b/drivers/net/ethernet/mellanox/mlx5/core/main.c
> > > > > @@ -1275,11 +1275,6 @@ static int mlx5_mdev_init(struct
> > > > > mlx5_core_dev *dev, int profile_idx)
> > > > > 
> > > > >  	priv->dbg_root = debugfs_create_dir(dev_name(dev-
> > > > > >device),
> > > > >  					    mlx5_debugfs_root);
> > > > > -	if (!priv->dbg_root) {
> > > > > -		dev_err(dev->device, "mlx5_core: error, Cannot
> > > > > create
> > > > > debugfs dir, aborting\n");
> > > > > -		goto err_dbg_root;
> > > 
> > > Actually, this removes the only use of err_dbg_root, so that
> > > should
> > > be
> > > removed at the same time.
> > > 
> > 
> > Fixed this up and applied to net-next-mlx5, 
> > Thanks!
> > 
> 
> Hi Saeed,
> 
> I see this warning in mainline now, is this something you were
> planning
> to have merged this cycle or next? I see it in several configs so it
> would be nice if it could be resolved this one, since it was
> introduced
> by a patch in this cycle even though the core issue has been around
> for
> a few months.
> 

Hi Nathan, 

I just pulled this patch into net-mlx5, and will send it out in my net
PR today.


Thanks,
Saeed.


> Cheers,
> Nathan