linux-kernel - Re: [PATCH] KVM: Add the check and free to avoid unknown errors.

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Message-ID: <CAB5KdOYgfhZX7ya3G3YFOpLehzagYfajBE+mVOgOd7dvD3vXqA@mail.gmail.com>
Date:   Sat, 15 Feb 2020 13:33:57 +0800
From:   Haiwei Li <lihaiwei.kernel@...il.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: Add the check and free to avoid unknown errors.

linmiaohe <linmiaohe@...wei.com> 于2020年2月15日周六 上午10:00写道：
>
> Hi:
> Haiwei Li <lihaiwei.kernel@...il.com> wrote:
> > From: Haiwei Li <lihaiwei@...cent.com>
> >
> > If 'kvm_create_vm_debugfs()' fails in 'kzalloc(sizeof(*stat_data), ...)', 'kvm_destroy_vm_debugfs()' will be called by the final fput(file) in 'kvm_dev_ioctl_create_vm()'.
> >
> > Add the check and free to avoid unknown errors.
>
> Add the check and free? According to the code,it seem what you mean is "add the check against free" ?

Right, i can change the description.

>
> >
> > Signed-off-by: Haiwei Li <lihaiwei@...cent.com>
> >
> >       if (kvm->debugfs_stat_data) {
> > -             for (i = 0; i < kvm_debugfs_num_entries; i++)
> > +             for (i = 0; i < kvm_debugfs_num_entries; i++) {
> > +                     if (!kvm->debugfs_stat_data[i])
> > +                             break;
> >                       kfree(kvm->debugfs_stat_data[i]);
> > +             }
> >               kfree(kvm->debugfs_stat_data);
> >       }
> >   }
>
> If (!kvm->debugfs_stat_data[i]) is checked in kfree() internal. And break early seems have no different effect.
> Could you please explain what unknown errors may occur? And how? Thanks.

I get the free() code. It is just like what you said. Thanks a lot.
Break early is useful. If kvm->debugfs_stat_data[i] is null, breaking
early can reduce the check.

>