mem: fix typo in determining an address of parent vma

Look at this hunk from 7659c995f58f:
-    paddr = decode_pointer(vma_premmaped_start(&p->vma));
+    paddr = decode_pointer(vma->premmaped_addr);

Obviously we want to use p->premmaped_addr instead of
vma->premmaped_addr.

Fixes: 7659c995f58f ("vm: don't overwrite vma->shmid for private mappings")
Reported-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
mem: stop searching a parent vma if we found one

A parent vma can be only one.

Fixes: 57d25e7cea12 ("mm: fix expression to determine which vma-s can be shared")
Reported-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
vma: don't skip vmas during searching a parent vma

We stop searching if vma->start is bigger than a required one.
The coursor is set on the last examined vma. When we are searching a
parent vma for the next vma, we start examine vma-s starting from
coursor->next, so we don't examine the vma, which is pointed by cursor.

This patch replaces list_for_each_entry_continue on list_for_each_entry_from.

Reported-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
dump: preserve the dumpable flag on criu dump/restore

Preserve the dumpable flag, which affects whether a core dump will be
generated, but also affects the ownership of the virtual files under
/proc/$pid after restoring a process.

Tested: Restored a process with a criu including this patch and looked
at /proc/$pid to confirm that the virtual files were no longer all owned
by root:root.

zdtm tests pass except for cow01 which seems to be broken.
(see https://bugzilla.openvz.org/show_bug.cgi?id=2967 for details.)

This patch fixes https://bugzilla.openvz.org/show_bug.cgi?id=2968

Signed-off-by: Filipe Brandenburger <filbranden@google.com>
Change-Id: I8c386508448a84368a86666f2d7500b252a78bbf
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>