linux-kernel - Re: [GIT PULL] BPF changes for 6.18

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Message-ID: <aN0d6PAFg5UTKuOc@krava>
Date: Wed, 1 Oct 2025 14:26:16 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	bpf@...r.kernel.org, daniel@...earbox.net, andrii@...nel.org,
	martin.lau@...nel.org, peterz@...radead.org, kuba@...nel.org,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	netdev@...r.kernel.org
Subject: Re: [GIT PULL] BPF changes for 6.18

On Wed, Oct 01, 2025 at 12:58:29PM +0200, Jiri Olsa wrote:
> On Tue, Sep 30, 2025 at 07:09:43PM -0700, Linus Torvalds wrote:
> > [ Jiri added to participants ]
> > 
> > On Sun, 28 Sept 2025 at 08:46, Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:
> > >
> > > Note, there is a trivial conflict between tip and bpf-next trees:
> > > in kernel/events/uprobes.c between commit:
> > >   4363264111e12 ("uprobe: Do not emulate/sstep original instruction when ip is changed")
> > > from the bpf-next tree and commit:
> > >   ba2bfc97b4629 ("uprobes/x86: Add support to optimize uprobes")
> > > from the tip tree:
> > > https://lore.kernel.org/all/aNVMR5rjA2geHNLn@sirena.org.uk/
> > > since Jiri's two separate uprobe/bpf related patch series landed
> > > in different trees. One was mostly uprobe. Another was mostly bpf.
> > 
> > So the conflict isn't complicated and I did it the way linux-next did
> > it, but honestly, the placement of that arch_uprobe_optimize() thing
> > isn't obvious.
> > 
> > My first reaction was to put it before the instruction_pointer()
> > check, because it seems like whatever rewriting the arch wants to do
> > might as well be done regardless.
> > 
> > It's very confusing how it's sometimes skipped, and sometimes not
> > skipped. For example. if the uprobe is skipped because of
> > single-stepping disabling it, the arch optimization still *will* be
> > done, because the "skip_sstep()" test is done after - but other
> > skipping tests are done before.
> > 
> > Jiri, it would be good to just add a note about when that optimization
> > is done and when not done. Because as-is, it's very confusing.
> > 
> > The answer may well be "it doesn't matter, semantics are the same" (I
> > suspect that _is_ the answer), but even so that current ordering is
> > just confusing when it sometimes goes through that
> > arch_uprobe_optimize() and sometimes skips it.
> 
> yes, either way will work fine, but perhaps the other way round to
> first optimize and then skip uprobe if needed is less confusing
> 
> > 
> > Side note: the conflict in the selftests was worse, and the magic to
> > build it is not obvious. It errors out randomly with various kernel
> > configs with useless error messages, and I eventually just gave up
> > entirely with a
> > 
> >    attempt to use poisoned ‘gettid’
> > 
> > error.
> > 
> >              Linus
> 
> I ended up with changes below, should I send formal patches?

I sent out the bpf selftest fixes:
  https://lore.kernel.org/bpf/20251001122223.170830-1-jolsa@kernel.org/T/#t

will send the uprobe fix shortly

jirka