linux-kernel - Re: [PATCH v2 5/5] Input: evdev

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Date:   Tue, 19 Jun 2018 11:33:16 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Shaohua Li <shli@...nel.org>, linux-raid@...r.kernel.org,
        linux-input@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, mika.westerberg@...ux.intel.com
Subject: Re: [PATCH v2 5/5] Input: evdev - Switch to bitmap_zalloc()

On Sat, Jun 16, 2018 at 12:42:31AM +0300, Yury Norov wrote:
> Hi Andy,
> 
> On Fri, Jun 15, 2018 at 04:20:17PM +0300, Andy Shevchenko wrote:
> > Switch to bitmap_zalloc() to show clearly what we are allocating.
> > Besides that it returns pointer of bitmap type instead of opaque void *.
> > 
> > Acked-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >  drivers/input/evdev.c | 16 +++++++---------
> >  1 file changed, 7 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> > index c81c79d01d93..370206f987f9 100644
> > --- a/drivers/input/evdev.c
> > +++ b/drivers/input/evdev.c
> > @@ -481,7 +481,7 @@ static int evdev_release(struct inode *inode, struct file *file)
> >         evdev_detach_client(evdev, client);
> > 
> >         for (i = 0; i < EV_CNT; ++i)
> > -               kfree(client->evmasks[i]);
> > +               bitmap_free(client->evmasks[i]);
> > 
> >         kvfree(client);
> > 
> > @@ -925,17 +925,15 @@ static int evdev_handle_get_val(struct evdev_client *client,
> >  {
> >         int ret;
> >         unsigned long *mem;
> > -       size_t len;
> > 
> > -       len = BITS_TO_LONGS(maxbit) * sizeof(unsigned long);
> > -       mem = kmalloc(len, GFP_KERNEL);
> > +       mem = bitmap_alloc(maxbit, GFP_KERNEL);
> >         if (!mem)
> >                 return -ENOMEM;
> 
> But in commit message you say you switch to bitmap_zalloc(). IIUC
> bitmap_alloc() is OK here. But could you please update comment to
> avoid confusing.
> 
> > 
> >         spin_lock_irq(&dev->event_lock);
> >         spin_lock(&client->buffer_lock);
> > 
> > -       memcpy(mem, bits, len);
> > +       bitmap_copy(mem, bits, maxbit);
> > 
> >         spin_unlock(&dev->event_lock);
> > 
> > @@ -947,7 +945,7 @@ static int evdev_handle_get_val(struct evdev_client *client,
> >         if (ret < 0)
> >                 evdev_queue_syn_dropped(client);
> > 
> > -       kfree(mem);
> > +       bitmap_free(mem);
> > 
> >         return ret;
> >  }
> > @@ -1003,13 +1001,13 @@ static int evdev_set_mask(struct evdev_client *client,
> >         if (!cnt)
> >                 return 0;
> > 
> > -       mask = kcalloc(sizeof(unsigned long), BITS_TO_LONGS(cnt), GFP_KERNEL);
> > +       mask = bitmap_zalloc(cnt, GFP_KERNEL);
> >         if (!mask)
> >                 return -ENOMEM;
> > 
> >         error = bits_from_user(mask, cnt - 1, codes_size, codes, compat);
> 
> If my understanding of bits_from_user() correct, here you can also use
> bitmap_alloc(), true?

bits_from_user() copies as much as user supplied, we want to zero out
the tail to make sure there is no garbage, so we want to use
kcalloc/kzalloc/bitmap_zalloc here.

Thanks.

-- 
Dmitry