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    SubjectRe: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3
    On Thu, Mar 08, 2012 at 08:05:34PM +0100, Oleg Nesterov wrote:
    ...
    > >
    > > Yes, exactly, I need to remove old mappings first (because VMAs
    > > we're about to restore may intersect with current map the host
    > > program has). And yes, once they all are removed I don't have
    > > /proc/pid/exe anymore. That's why I need num_exe_file_vmas == 0
    > > case.
    >
    > OK, in this case PR_SET_MM_EXE_FILE should probably fail if
    > mm->num_exe_file_vmas != 0 ? This way it would be more or less
    > consistent or at least understandable. Just we add the new
    > special case: num_exe_file_vmas == 0 but exe_file != NULL
    > because c/r people are crazy.
    >

    Sure, I can drop num_exe_file_vmas != 0 case and refuse to
    setup new exe symlink if there some VM_EXECUTABLE remains
    unmapped. Sounds good?

    > > > And I don't think the unconditional
    > > >
    > > > down_write(&mm->mmap_sem);
    > > > set_mm_exe_file(mm, exe_file);
    > > > up_write(&mm->mmap_sem);
    > > >
    > > > is 100% right, this clears ->num_exe_file_vmas. This means that
    > > > (if you still have the old mapping) the new exe_file can go away
    > > > after added_exe_file_vma() + removed_exe_file_vma(). Normally this
    > > > should happen, but afaics this is possible. Note that even, say,
    > > > mprotect() can trigger added_exe_file_vma().
    > > >
    > >
    > > Wait, Oleg, I'm confused, in case if there *is* exitsting VM_EXECUTABLEs
    > > then we jump into first banch and simply replace old exe_file.
    >
    > Yes. And then later you remove the old mapping (which do not match
    > the new file anyway) and the new exe_file goes away. Unlikely you
    > want this.

    Yes, unlikely ;)

    Cyrill


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