mm/hugetlb.c: fix resv map memory leak for placeholder entries

mm/hugetlb.c: fix resv map memory leak for placeholder entries

Orabug: 22302415

Dmitry Vyukov reported the following memory leak

unreferenced object 0xffff88002eaafd88 (size 32):
  comm "a.out", pid 5063, jiffies 4295774645 (age 15.810s)
  hex dump (first 32 bytes):
    28 e9 4e 63 00 88 ff ff 28 e9 4e 63 00 88 ff ff  (.Nc....(.Nc....
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<     inline     >] kmalloc include/linux/slab.h:458
    [<ffffffff815efa64>] region_chg+0x2d4/0x6b0 mm/hugetlb.c:398
    [<ffffffff815f0c63>] __vma_reservation_common+0x2c3/0x390 mm/hugetlb.c:1791
    [<     inline     >] vma_needs_reservation mm/hugetlb.c:1813
    [<ffffffff815f658e>] alloc_huge_page+0x19e/0xc70 mm/hugetlb.c:1845
    [<     inline     >] hugetlb_no_page mm/hugetlb.c:3543
    [<ffffffff815fc561>] hugetlb_fault+0x7a1/0x1250 mm/hugetlb.c:3717
    [<ffffffff815fd349>] follow_hugetlb_page+0x339/0xc70 mm/hugetlb.c:3880
    [<ffffffff815a2bb2>] __get_user_pages+0x542/0xf30 mm/gup.c:497
    [<ffffffff815a400e>] populate_vma_page_range+0xde/0x110 mm/gup.c:919
    [<ffffffff815a4207>] __mm_populate+0x1c7/0x310 mm/gup.c:969
    [<ffffffff815b74f1>] do_mlock+0x291/0x360 mm/mlock.c:637
    [<     inline     >] SYSC_mlock2 mm/mlock.c:658
    [<ffffffff815b7a4b>] SyS_mlock2+0x4b/0x70 mm/mlock.c:648

Dmitry identified a potential memory leak in the routine region_chg, where
a region descriptor is not free'ed on an error path.

However, the root cause for the above memory leak resides in region_del.
In this specific case, a "placeholder" entry is created in region_chg.
The associated page allocation fails, and the placeholder entry is left in
the reserve map.  This is "by design" as the entry should be deleted when
the map is released.  The bug is in the region_del routine which is used
to delete entries within a specific range (and when the map is released).
region_del did not handle the case where a placeholder entry exactly
matched the start of the range range to be deleted.  In this case, the
entry would not be deleted and leaked.  The fix is to take these special
placeholder entries into account in region_del.

The region_chg error path leak is also fixed.

Fixes: feba16e25a57 ("mm/hugetlb: add region_del() to delete a specific range of entries")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: <stable@vger.kernel.org>	[4.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 8ea87f6c208bd070a2701b53d2479a415f4159f4)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>