mm: enable page poisoning early at boot

mm: enable page poisoning early at boot

On SPARSEMEM systems page poisoning is enabled after buddy is up,
because of the dependency on page extension init.  This causes the pages
released by free_all_bootmem not to be poisoned.  This either delays or
misses the identification of some issues because the pages have to
undergo another cycle of alloc-free-alloc for any corruption to be
detected.

Enable page poisoning early by getting rid of the PAGE_EXT_DEBUG_POISON
flag.  Since all the free pages will now be poisoned, the flag need not
be verified before checking the poison during an alloc.

[[email protected]: fix Kconfig]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Vinayak Menon <[email protected]>
Acked-by: Laura Abbott <[email protected]>
Tested-by: Laura Abbott <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Akinobu Mita <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>