On Wed, Sep 08, 2021 at 10:52:59AM -0700, Andrew Morton wrote: > On Wed, 8 Sep 2021 10:21:18 -0700 Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > > > Again I am ignorant on the details so if you can clarify the following > > > it may help me and others to better understand the problem: > > > > > > 1. Peter's patch appears to just take the same "fallback" path > > > that would be taken if the trylock failed. > > > Is this really a breakage or just loss of performance ? > > > I would expect the latter, since it is called "fallback". > > > > As Yonghong explained it's a user space breakage. > > User space tooling expects build_id to be available 99.999% of the time > > and that's what users observed in practice. > > They've built a bunch of tools on top of this feature. > > The data from these tools goes into various datacenter tables > > and humans analyze it later. > > So Peter's proposal is not acceptable. We don't want to get yelled at. > > > > I'm not understanding. Peter said "this patch merely removes a > performance tweak" and you and Yonghong said "it breaks userspace". > These assertions are contradictory! Peter said: "The only sane approach is making the vma tree lockless, but so far the bpf people have resisted doing the right thing because they've been allowed to get away with these atrocities. " which is partially true. bpf folks didn't resist it. There is work ongoing to make it lockless. It just takes an long time. I don't see how bpf folks can speed it up any further. > Please describe the expected userspace-visible change from Peter's > patch in full detail? User space expects build_id to be available. Peter patch simply removes that feature. > And yes, it is far preferable that we resolve this by changing BPF to > be a better interface citizen, please. Let's put those thinking caps on? Just silence a lockdep as Yonghong proposed or some other way, since it's only a lockdep issue. There is no actual breakage. The feature was working and still works as intended.
