hugetlbfs: revert "use i_mmap_rwsem for more pmd sharing synchronization"

This reverts b43a9990055958e70347c56f90ea2ae32c67334c

The reverted commit caused issues with migration and poisoning of anon
huge pages.  The LTP move_pages12 test will cause an "unable to handle
kernel NULL pointer" BUG would occur with stack similar to:

  RIP: 0010:down_write+0x1b/0x40
  Call Trace:
    migrate_pages+0x81f/0xb90
    __ia32_compat_sys_migrate_pages+0x190/0x190
    do_move_pages_to_node.isra.53.part.54+0x2a/0x50
    kernel_move_pages+0x566/0x7b0
    __x64_sys_move_pages+0x24/0x30
    do_syscall_64+0x5b/0x180
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

The purpose of the reverted patch was to fix some long existing races
with huge pmd sharing.  It used i_mmap_rwsem for this purpose with the
idea that this could also be used to address truncate/page fault races
with another patch.  Further analysis has determined that i_mmap_rwsem
can not be used to address all these hugetlbfs synchronization issues.
Therefore, revert this patch while working an another approach to the
underlying issues.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Kravetz <[email protected]>
Reported-by: Jan Stancek <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: "Aneesh Kumar K . V" <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Prakash Sangappa <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions