Re: [more fun] Re: locking question: do_mmap(), do_munmap()

[kanoj@google.engr.sgi.com (Kanoj Sarcar)]

> 
> Alexander Viro wrote:
> > Another one: ptrace_readdata() -> access_process_vm() -> find_extend_vma()
> > -> make_pages_present(). Again, no mmap_sem in sight.

Actually, I think access_process_vm() does get mmap_sem, although
after doing the find_extend_vma, which should be fixed. I will take
care of it in my patch.

> 
> Can 2 processes ptrace() each other? If yes, then this will lock-up if
> you acquire the mmap_sem.
>

Theoretically, there is no problem with 2 processes ptrace()ing each other.
IMO, no deadlock is possible in the approach I posted.

Kanoj

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