Re: [PATCH] [RFC] bpf: tracing: new helper bpf_get_current_cgroup_ino

On 05/23/2018 06:31 AM, Y Song wrote:

On Tue, May 22, 2018 at 8:35 PM, Alexei Starovoitov
[off-list ref] wrote:

quoted

On Tue, May 22, 2018 at 08:33:24PM -0700, Y Song wrote:

quoted

+       struct cgroup *cgrp = task_dfl_cgroup(current);
+       if (!cgrp)
+               return -EINVAL;

why this check is needed?

No reason :-) Originally I am concerned whether it is possible cgrp
could be NULL.
By looking at the code, it SEEMS to me that it could not be NULL, but I am not
100% sure (as I am not a cgroup expert). Since you are asking,
probably means it cannot be NULL, so will remove it in formal upstream patch.

Aside from this the cgrp->kn->id.id is also u64, so overlapping this with
error codes we'll get into a similar issue as with bpf_perf_event_read().