On Tue, Feb 4, 2025 at 3:19 PM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > On Mon, Jan 27, 2025 at 04:15:01PM +0100, Paolo Bonzini wrote: > > On Mon, Jan 27, 2025 at 3:10 PM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > On 01/26, Linus Torvalds wrote: > > > > On Sun, 26 Jan 2025 at 10:54, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > > > > > > > > I don't think we even need to detect the /proc/self/ or /proc/self-thread/ > > > > > case, next_tid() can just check same_thread_group, > > > > > > > > That was my thinking yes. > > > > > > > > If we exclude them from /proc/*/task entirely, I'd worry that it would > > > > hide it from some management tool and be used for nefarious purposes > > > > > > Agreed, > > > > > > > (even if they then show up elsewhere that the tool wouldn't look at). > > > > > > Even if we move them from /proc/*/task to /proc ? > > > > Indeed---as long as they show up somewhere, it's not worse than it > > used to be. The reason why I'd prefer them to stay in /proc/*/task is > > that moving them away at least partly negates the benefits of the > > "workers are children of the starter" model. For example it > > complicates measuring their cost within the process that runs the VM. > > Maybe it's more of a romantic thing than a real practical issue, > > because in the real world resource accounting for VMs is done via > > cgroups. But unlike the lazy creation in KVM, which is overall pretty > > self-contained, I am afraid the ugliness in procfs would be much worse > > compared to the benefit, if there's a benefit at all. > > > > > Perhaps, I honestly do not know what will/can confuse userspace more. > > > > At the very least, marking workers as "Kthread: 1" makes sense and > > should not cause too much confusion. I wouldn't go beyond that unless > > we get more reports of similar issues, and I'm not even sure how > > common it is for userspace libraries to check for single-threadedness. > > Sorry, just saw this thread now. > > What if we did what Linus suggests and hide (odd) user workers from > /proc/<pid>/task/* but also added /proc/<pid>/workers/*. The latter > would only list the workers that got spawned by the kernel for that > particular task? This would acknowledge their somewhat special status > and allow userspace to still detect them as "Hey, I didn't actually > spawn those, they got shoved into my workload by the kernel for me.". Wouldn't the workers then disappear completely from ps, top or other tools that look at /proc/$PID/task? That seems a bit too underhanded towards userspace... Paolo > (Another (ugly) alternative would be to abuse prctl() and have workloads > opt-in to hiding user workers from /proc/<pid>/task/.)
