mm, thp: fix incorrect unmap behavior for private pages

When truncating pagecache on file THP, the private pages of a process
should not be unmapped mapping.  This incorrect behavior on a dynamic
shared libraries which will cause related processes to happen core dump.

A simple test for a DSO (Prerequisite is the DSO mapped in file THP):

    int main(int argc, char *argv[])
    {
	int fd;

	fd = open(argv[1], O_WRONLY);
	if (fd < 0) {
		perror("open");
	}

	close(fd);
	return 0;
    }

The test only to open a target DSO, and do nothing.  But this operation
will lead one or more process to happen core dump.  This patch mainly to
fix this bug.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs")
Signed-off-by: Rongwei Wang <[email protected]>
Tested-by: Xu Yu <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Song Liu <[email protected]>
Cc: William Kucharski <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Collin Fijalkovich <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions