tree 49215f2dcf4fe1ee902650a3c592897057395d73
parent b4dff2874006e54b60ce4f4dbcfec9ab81c6aff4
author Vineet Gupta <vgupta@synopsys.com> 1469730950 -0700
committer Vineet Gupta <vgupta@synopsys.com> 1469734697 -0700

ARC: mm: don't loose PTE_SPECIAL in pte_modify()

LTP madvise05 was generating mm splat

| [ARCLinux]# /sd/ltp/testcases/bin/madvise05
| BUG: Bad page map in process madvise05  pte:80e08211 pmd:9f7d4000
| page:9fdcfc90 count:1 mapcount:-1 mapping:  (null) index:0x0 flags: 0x404(referenced|reserved)
| page dumped because: bad pte
| addr:200b8000 vm_flags:00000070 anon_vma:  (null) mapping:  (null) index:1005c
| file:  (null) fault:  (null) mmap:  (null) readpage:  (null)
| CPU: 2 PID: 6707 Comm: madvise05

And for newer kernels, the system was rendered unusable afterwards.

The problem was mprotect->pte_modify() clearing PTE_SPECIAL (which is
set to identify the special zero page wired to the pte).
When pte was finally unmapped, special casing for zero page was not
done, and instead it was treated as a "normal" page, tripping on the
map counts etc.

This fixes ARC STAR 9001053308

Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>