Re: [PATCH] tracing: Fix WARN_ON in tracing_buffers_mmap_close

[Vincent Donnefort]

On Fri, Feb 27, 2026 at 10:10:02AM -0500, Steven Rostedt wrote:
> On Fri, 27 Feb 2026 10:41:17 +0000
> Vincent Donnefort <vdonnefort@xxxxxxxxxx> wrote:
> 
> > > Hum, not sure this is entirely correct. We do set VM_DONTCOPY when creating the
> > > mapping (see __rb_map_vma). So AFAICT ->open() is not called in this situation (see
> > > dup_mmap())  
> > 
> > Ah right, Syzkaller is using madvise(MADVISE_DOFORK) which resets VM_DONTCOPY.
> 
> Hmm,
> 
> So this means user space can override the DONTCOPY? Can this cause bugs
> elsewhere that DONTCOPY is used?

Indeed, user space can clear DONTCOPY... unless we also set VM_IO. 

> 
> -- Steve