Re: [PATCH v5 tip/perf/core 1/2] uprobes: simplify find_active_uprobe_rcu() VMA checks

[Oleg Nesterov]

On 11/26, Jann Horn wrote:
>
> On Fri, Nov 22, 2024 at 4:59 AM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
> > At the point where find_active_uprobe_rcu() is used we know that VMA in
> > question has triggered software breakpoint, so we don't need to validate
> > vma->vm_flags. Keep only vma->vm_file NULL check.
>
> How do we know that the VMA we find triggered a software breakpoint?
> Between the time a software breakpoint was hit and the time we took
> the mmap_read_lock(), the VMA could have been replaced with an
> entirely different one, right?

Right, but this doesn't really differ from the case when another thread
replaces (or even unmaps) this VMA after find_active_uprobe_rcu() drops
mm->mmap_lock and returns a found uprobe.

So I think this is fine.

Oleg.