Re: [PATCH][RFT](2) minimal rmap for 2.5 - akpm tested

[Andrew Morton]

Rik van Riel wrote:
> 
> Hi,
> 
> Almost the same patch as before, except this one has had
> a few hours of testing by Andrew Morton and two bugs have
> been ironed out, most notably the truncate_complete_page()
> race.  This patch is probably safe since Andrew got bored
> when no new bugs showed up ...
> 

The box died, but not due to rmap.  We have a lock ranking
bug:

        do_exit
        ->mmput
          ->exit_mmap                           page_table_lock
            ->removed_shared_vm_struct
              ->lock_vma_mappings               i_shared_lock

versus

        do_truncate
        ->notify_change
          ->inode_setattr
            ->vmtruncate                        i_shared_lock
              ->vmtruncate_list
                ->zap_page_range                page_table_lock

It seems that in 2.5.16, a call to remove_shared_vm_struct() was
added to exit_mmap(), inside mm->page_table_lock.

That ranking conflicts with truncate.

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