Re: [PATCH 11/12] pid: rewrite task helper functions avoiding task->pid and task->tgid

Peter Zijlstra <peterz(a)infradead.org&gt; writes: No there is not and that is not a concern. Now I had thought given how the perf subsystem was constructed that only the god like root was even allowed to use the code. But it turns out there is sysctl_perf_event_paranoid that can bet twiddled that in some circumstance that unprivileged users are allowed to use perf. Which ultimately means perf will return the wrong data. Meaning that perf is broken by design and perf has no excuse to be using task->pid. Similarly every other place in the kernel that has made the same mistake. I mention perf explicitly for two reasons. perf gets the namespace handling horribly wrong, perf is the only place in the kernel where we are accessing pids frequently enough for an extra cache line miss to be a concern. When really pids in the kernel what we care about is not some stupid number but the stuct pid which points to that tasks, process groups, and sessions. You know the object that a pid is the name for. So yes as a long term direction task->pid and task->tgid need to be killed because we keep getting subsystems like perf that return the wrong data to userspace, or perform the wrong checks, because the current structure makes it seem like it is ok to do the wrong thing. Now that should not be Richard's fight. Hopefully he can focus on fixing audit. Which is why a special printf format is likely a good idea because it means you can easily print pids without needing to call ungainly helper functions. Of course you can't run kernels without this ``namespace'' stuff enabled. The best you can do is run kernels without the ability to create new instances of the namespaces. But it is so much better than having to look up task->pid in a hash table to get anything done, which is the previous state of affairs. When the pid namespace support was merged except for a few overlooked corner cases everything was converted except a bunch of printk statements. Now I look in the kernel and we have had subsystems added that totally get the namespace handling wrong because it is easy and apparently socially acceptable to mess up other peoples hard work. Apparently even Linus yelling at people a few years back wasn't enough for people to wake up and be responsible developers and use proper abstractions. So the only valid long term direction I can see is to remove all of the abstractions that make getting pid handling wrong, and to fix all of the code that gets it wrong today. So that there are no more bad examples in the kernel. This isn't Richard's fight, and this isn't what needs to happen with audit. Audit just needs to be fixed so that so that it reports pid numbers the audit daemon can make sense of, and to do that the audit should use helper functions that are pid namespace aware and make it clear that the proper pid namespace is being used. In the long term ->pid and ->tgid must die, and take all of this wrong think with it. Eric