On Tue, Mar 03, 2020 at 06:46:23PM +1100, Michael Ellerman wrote:
> Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> writes:
> > When calling debugfs functions, there is no need to ever check the
> > return value. The function can work or not, but the code logic should
> > never do something different based on this.
>
> Except it does need to do something different, if the file was created
> it needs to be removed in the remove path.
>
> > diff --git a/arch/powerpc/kvm/timing.c b/arch/powerpc/kvm/timing.c
> > index bfe4f106cffc..8e4791c6f2af 100644
> > --- a/arch/powerpc/kvm/timing.c
> > +++ b/arch/powerpc/kvm/timing.c
> > @@ -207,19 +207,12 @@ static const struct file_operations kvmppc_exit_timing_fops = {
> > void kvmppc_create_vcpu_debugfs(struct kvm_vcpu *vcpu, unsigned int id)
> > {
> > static char dbg_fname[50];
> > - struct dentry *debugfs_file;
> >
> > snprintf(dbg_fname, sizeof(dbg_fname), "vm%u_vcpu%u_timing",
> > current->pid, id);
> > - debugfs_file = debugfs_create_file(dbg_fname, 0666,
> > - kvm_debugfs_dir, vcpu,
> > - &kvmppc_exit_timing_fops);
> > -
> > - if (!debugfs_file) {
> > - printk(KERN_ERR"%s: error creating debugfs file %s\n",
> > - __func__, dbg_fname);
> > - return;
> > - }
> > + debugfs_create_file(dbg_fname, 0666, kvm_debugfs_dir, vcpu,
> > + &kvmppc_exit_timing_fops);
> > +
> >
> > vcpu->arch.debugfs_exit_timing = debugfs_file;
Ugh, you are right, how did I miss that? How is 0-day missing this?
It's been in my tree for a long time, odd.
> > }
>
> This doesn't build:
>
> arch/powerpc/kvm/timing.c:217:35: error: 'debugfs_file' undeclared (first use in this function); did you mean 'debugfs_file_put'?
>
> We can't just drop the assignment, we need the dentry to do the removal:
>
> void kvmppc_remove_vcpu_debugfs(struct kvm_vcpu *vcpu)
> {
> if (vcpu->arch.debugfs_exit_timing) {
> debugfs_remove(vcpu->arch.debugfs_exit_timing);
> vcpu->arch.debugfs_exit_timing = NULL;
> }
> }
>
>
> I squashed this in, which seems to work:
>
> diff --git a/arch/powerpc/kvm/timing.c b/arch/powerpc/kvm/timing.c
> index 8e4791c6f2af..5b7a66f86bd5 100644
> --- a/arch/powerpc/kvm/timing.c
> +++ b/arch/powerpc/kvm/timing.c
> @@ -207,19 +207,19 @@ static const struct file_operations kvmppc_exit_timing_fops = {
> void kvmppc_create_vcpu_debugfs(struct kvm_vcpu *vcpu, unsigned int id)
> {
> static char dbg_fname[50];
> + struct dentry *debugfs_file;
>
> snprintf(dbg_fname, sizeof(dbg_fname), "vm%u_vcpu%u_timing",
> current->pid, id);
> - debugfs_create_file(dbg_fname, 0666, kvm_debugfs_dir, vcpu,
> - &kvmppc_exit_timing_fops);
> -
> + debugfs_file = debugfs_create_file(dbg_fname, 0666, kvm_debugfs_dir,
> + vcpu, &kvmppc_exit_timing_fops);
>
> vcpu->arch.debugfs_exit_timing = debugfs_file;
That works, yes.
> }
>
> void kvmppc_remove_vcpu_debugfs(struct kvm_vcpu *vcpu)
> {
> - if (vcpu->arch.debugfs_exit_timing) {
> + if (!IS_ERR_OR_NULL(vcpu->arch.debugfs_exit_timing)) {
> debugfs_remove(vcpu->arch.debugfs_exit_timing);
> vcpu->arch.debugfs_exit_timing = NULL;
> }
No, this can just be:
debugfs_remove(vcpu->arch.debugfs_exit_timing);
No need to check anything, just call it and the debugfs code can handle
it just fine.
thanks,
greg k-h
