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SubjectRe: [PATCH v15 05/15] tracing: Add conditional snapshot
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Hi Steve,

On Thu, 2019-02-14 at 18:11 -0500, Steven Rostedt wrote:
> On Wed, 13 Feb 2019 17:42:45 -0600
> Tom Zanussi <zanussi@kernel.org> wrote:
>
> > +
> > +/**
> > + * tracing_snapshot_cond_enable - enable conditional snapshot for
> > an instance
> > + * @tr: The tracing instance
> > + * @cond_data: User data to associate with the snapshot
> > + * @update: Implementation of the cond_snapshot update
> > function
> > + *
> > + * Check whether the conditional snapshot for the given instance
> > has
> > + * already been enabled, or if the current tracer is already using
> > a
> > + * snapshot; if so, return -EBUSY, else create a cond_snapshot and
> > + * save the cond_data and update function inside.
> > + *
> > + * Returns 0 if successful, error otherwise.
> > + */
> > +int tracing_snapshot_cond_enable(struct trace_array *tr, void
> > *cond_data,
> > + cond_update_fn_t update)
> > +{
> > + struct cond_snapshot *cond_snapshot;
> > + int ret = 0;
> > +
> > + cond_snapshot = kzalloc(sizeof(*cond_snapshot),
> > GFP_KERNEL);
> > + if (!cond_snapshot)
> > + return -ENOMEM;
> > +
> > + cond_snapshot->cond_data = cond_data;
> > + cond_snapshot->update = update;
> > +
> > + mutex_lock(&trace_types_lock);
> > +
> > + ret = tracing_alloc_snapshot_instance(tr);
> > + if (ret)
> > + goto fail_unlock;
> > +
> > + if (tr->current_trace->use_max_tr) {
> > + ret = -EBUSY;
> > + goto fail_unlock;
> > + }
> > +
> > + if (tr->cond_snapshot) {
> > + ret = -EBUSY;
> > + goto fail_unlock;
> > + }
> > +
> > + arch_spin_lock(&tr->max_lock);
> > + tr->cond_snapshot = cond_snapshot;
> > + arch_spin_unlock(&tr->max_lock);
> > +
> > + mutex_unlock(&trace_types_lock);
> > +
> > + return ret;
> > +
> > + fail_unlock:
> > + mutex_unlock(&trace_types_lock);
> > + kfree(cond_snapshot);
> > + return ret;
>
> Some whitespace damage here. No need to resend, I fixed it.
>

OK, thanks.

>
> > +}
> > +EXPORT_SYMBOL_GPL(tracing_snapshot_cond_enable);
> > +
>
> I also added this change on top of your series.
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 0460cc0f28fd..2cf3c747a357 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1116,6 +1116,14 @@ int tracing_snapshot_cond_enable(struct
> trace_array *tr, void *cond_data,
> goto fail_unlock;
> }
>
> + /*
> + * The cond_snapshot can only change to NULL without the
> + * trace_types_lock. We don't care if we race with it going
> + * to NULL, but we want to make sure that it's not set to
> + * something other than NULL when we get here, which we can
> + * do safely with only holding the trace_types_lock and not
> + * having to take the max_lock.
> + */
> if (tr->cond_snapshot) {
> ret = -EBUSY;
> goto fail_unlock;
>

Looks good, thanks for adding that back.

Tom

> I'll start testing your series now.
>
> Thanks!
>
> -- Steve
>

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