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Date: Tue, 03 Mar 2020 18:46:23 +1100
From: Michael Ellerman <mpe@...erman.id.au>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linuxppc-dev@...ts.ozlabs.org
Cc: linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Paul Mackerras <paulus@...abs.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 2/6] powerpc: kvm: no need to check return value of debugfs_create functions
Greg Kroah-Hartman <gregkh@...uxfoundation.org> 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;
> }
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;
}
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;
}
cheers
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