[BUG] Bad page flags when process using mlock()ed memory exits

[Peter Chubb]

In recent kernels I've been seeing many mesages of the form:

BUG: Bad page state in process reiserfsck  pfn:79c58
page:c3d03b00 flags:8050000c count:0 mapcount:0 mapping:(null) index:8095
Pid: 3927, comm: reiserfsck Not tainted 2.6.30-test-05456-gda456f1 #60
Call Trace:
 [<c134a67c>] ? printk+0xf/0x13
 [<c10774dc>] bad_page+0xc9/0xe2
 [<c1078041>] free_hot_cold_page+0x5c/0x204
 [<c1078206>] __pagevec_free+0x1d/0x25
 [<c107ac3e>] release_pages+0x14e/0x18e)
 [<c108ef8a>] free_pages_and_swap_cache+0x69/0x82
 [<c1089458>] exit_mmap+0xf6/0x11f
 [<c102afcd>] mmput+0x39/0xaf
 [<c102e534>] exit_mm+0xe5/0xed
 [<c102fa66>] do_exit+0x13f/0x578
 [<c102fefd>] do_group_exit+0x5e/0x85
 [<c102ff37>] sys_exit_group+0x13/0x17
 [<c10031ef>] sysenter_do_call+0x12/0x3c
Disabling lock debugging due to kernel taint

This appears to have been introduced by patch 
    da456f14d2f2d7350f2b9440af79c85a34c7eed5
    page allocator: do not disable interrupts in free_page_mlock()

That patch removed the free_page_mlock() from free_pages_check(), so
if free_hot_cold_page() is called on an Mlocked page (e.g., if a
process that used mlock() calls exit()) free_pages_check() will always
barf, whereas before it would just unlock the page.

Reverting the patch fixed the issue for me (although a straight git
revert isn't enough, because free_page_mlock() has moved from
mm/internal.h to mm/page_alloc.c)

--
Dr Peter Chubb                              peter DOT chubb AT nicta.com.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia
           Kernel Engineering Group (KEG): Where Systems Brew.
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