Re: [PATCH] uprobes: Skip breakpoint installation on non executable vmas

[Oleg Nesterov <oleg@redhat.com>]

On 08/05, Andrii Nakryiko wrote:
>
> On Wed, Aug 5, 2026 at 8:14 AM Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > On 08/05, Sumanth Korikkar wrote:
> > >
> > > bpftrace  -e 'usdt:./testprogs/usdt_semaphore_test:tracetest:testprobe {
> > > printf("%s\n", str(arg1) ); exit(); }'
> >
>
> does bpftrace care if USDT semaphore is set to 1 or 2, it shouldn't.
> As long as detaching decrements it from 2 back to zero we should be
> fine. Is that what's happening? If so, is there really a problem
> needing to be fixed?

Yes, I thought about that too...

> > So, 2 vmas map the same binary, install_breakpoint() is called twice.
> > But, the 2nd install_breakpoint() -> ... -> uprobe_write() should see
> > that the original insn was already replaced by int3, in this case
> > verify_opcode() returns 0 and uprobe_write() should do nothing.
> >
> > And, if this uprobe was optimized before the 2nd install_breakpoint(),
> > uprobe_write() won't be called.
> >
> > Hmm.
>
> Even though it's the same file offset, it is mapped to two different
> virtual addresses, so I think it should be two different memory pages
> that will have two separate int3 instructions. I don't think there is
> any contradiction or surprise, is there?

Ah, indeed I am stupid ;)

Yes, uprobe_write() creates the COW'ed anonymous page, so the 1st
install_breakpoint() won't affect the 2nd mapping to the same binary.

Thanks Andrii!

Oleg.