Re: [PATCH 1/4] oprofile: Handle initialisation failure more gracefully

Robert Richter
2010-08-27T16:41:08Z

On 27.08.10 11:15:25, Will Deacon wrote:

> > > The current implementation is not entirely safe in the case that
> > > oprofile_arch_init() fails. We need to make sure that we always call
> > > exit_driverfs() if we've called init_driverfs(). Also, avoid a potential
> > > double free when freeing 'counter_config', e.g. don't free
> > > 'counter_config' in both oprofile_arch_init() and oprofile_arch_exit().

I am not sure if it is worth the memory handling code, we could
alternativly implement fixed size arrays with MAX_COUNTERS. This would
eas it a lot. But, this code will become generic, so we can stick with
this implementation.

But, cpu varables should be used, maybe with a later patch.

> > The root cause that makes this check necessary is that
> > oprofile_arch_exit() is called though oprofile_arch_init() failed. We
> > should better fix this instead. I have to admit we will then have to
> > check all architectural implementations.
> >
>
> I took a look through all of the oprofile_arch_{init,exit} functions
> and it looks like only ARM needs fixing. Nobody else does any allocation
> here [well, until Matt's unified version comes into play].

Great, many thanks.

> How about something like this? This removes the exit call
> from the init code and sets pointers to NULL after they have been
> freed. We still have to do some checking so that we don't try to
> release a NULL perf event:
>
> diff --git a/arch/arm/oprofile/common.c b/arch/arm/oprofile/common.c
> index 0691176..12253eb 100644
> --- a/arch/arm/oprofile/common.c
> +++ b/arch/arm/oprofile/common.c
> @@ -275,10 +275,12 @@ out:
> return ret;
> }
>
> -static void exit_driverfs(void)
> +static void __exit exit_driverfs(void)
> {
> - platform_device_unregister(oprofile_pdev);
> - platform_driver_unregister(&oprofile_driver);
> + if (!IS_ERR_OR_NULL(oprofile_pdev)) {

This check is obsolete here as we do not call oprofile_arch_exit() on
failure.

> + platform_device_unregister(oprofile_pdev);
> + platform_driver_unregister(&oprofile_driver);
> + }
> }
> #else
> static int __init init_driverfs(void) { return 0; }
> @@ -365,6 +367,7 @@ int __init oprofile_arch_init(struct
> oprofile_operations *ops)
> ret = init_driverfs();
> if (ret) {
> kfree(counter_config);
> + counter_config = NULL;

Dito, obsolete now.

> return ret;
> }
>
> @@ -374,8 +377,10 @@ int __init oprofile_arch_init(struct
> oprofile_operations *ops)
> if (!perf_events[cpu]) {
> pr_info("oprofile: failed to allocate %d perf events "
> "for cpu %d\n", perf_num_counters, cpu);
> - while (--cpu >= 0)
> + while (--cpu >= 0) {
> kfree(perf_events[cpu]);
> + perf_events[cpu] = NULL;
> + }

counter_config must be freed here.

> return -ENOMEM;
> }
> }
> @@ -396,25 +401,27 @@ int __init oprofile_arch_init(struct
> oprofile_operations *ops)
> return ret;
> }
>
> -void oprofile_arch_exit(void)
> +void __exit oprofile_arch_exit(void)
> {
> int cpu, id;
> struct perf_event *event;
>
> - if (*perf_events) {
> - exit_driverfs();
> - for_each_possible_cpu(cpu) {
> - for (id = 0; id < perf_num_counters; ++id) {
> - event = perf_events[cpu][id];
> - if (event != NULL)
> - perf_event_release_kernel(event);
> - }
> - kfree(perf_events[cpu]);
> + exit_driverfs();

If we shutdown all this in reverse order, this should be after the
loop.

> +
> + for_each_possible_cpu(cpu) {
> + if (!perf_events[cpu])
> + continue;

Should be never NULL, the check can be removed.

> +
> + for (id = 0; id < perf_num_counters; ++id) {
> + event = perf_events[cpu][id];
> + if (event != NULL)

if (event)
...

> + perf_event_release_kernel(event);
> }
> +
> + kfree(perf_events[cpu]);
> }
>
> - if (counter_config)
> - kfree(counter_config);
> + kfree(counter_config);
> }
> #else
> int __init oprofile_arch_init(struct oprofile_operations *ops)
> @@ -422,5 +429,5 @@ int __init oprofile_arch_init(struct
> oprofile_operations *ops)
> pr_info("oprofile: hardware counters not available\n");
> return -ENODEV;
> }
> -void oprofile_arch_exit(void) {}
> +void __exit oprofile_arch_exit(void) {}
> #endif /* CONFIG_HW_PERF_EVENTS */
> diff --git a/drivers/oprofile/oprof.c b/drivers/oprofile/oprof.c
> index b336cd9..3094af0 100644
> --- a/drivers/oprofile/oprof.c
> +++ b/drivers/oprofile/oprof.c
> @@ -257,15 +257,11 @@ static int __init oprofile_init(void)
> printk(KERN_INFO "oprofile: using timer interrupt.\n");
> err = oprofile_timer_init(&oprofile_ops);
> if (err)
> - goto out_arch;
> + goto out;

A 'return err;' here would remove the goto. I would preffer this.

Thanks,

-Robert

> }
> err = oprofilefs_register();
> - if (err)
> - goto out_arch;
> - return 0;
>
> -out_arch:
> - oprofile_arch_exit();
> +out:
> return err;
> }
>
>
> Thanks,
>
> Will
>
>

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