LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set")

From	Will Deacon <will.deacon@arm.com>
Newsgroups	linux.kernel
Subject	LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set")
Date	2015-09-14 13:00 +0200
Message-ID	<q8zEl-3YR-3@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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Hi Kirill,

Your patch 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set")
causes some mmap regressions in LTP, which appears to use a MAP_PRIVATE
mmap of /dev/zero as a way to get anonymous pages in some of its tests
(specifically mmap10 [1]).

Dead simple reproducer below. Is this change in behaviour intentional?

Will

[1]
http://sourceforge.net/p/ltp/git/ci/1eb440c2b5fe43a3e5023015a16aa5d7d3385b1e/tree/testcases/kernel/syscalls/mmap/mmap10.c

--->8

#include <sys/mman.h>
#include <sys/stat.h>

#include <fcntl.h>
#include <stdio.h>

#define MAP_SZ	5*1024*1024

int main(void)
{
	char *foo;
	int fd;

	fd = open("/dev/zero", O_RDWR, 0666);
	if (fd < 0) {
		perror(NULL);
		return fd;
	}

	foo = mmap(NULL, MAP_SZ, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
	if (foo == MAP_FAILED) {
		perror(NULL);
		return -1;
	}

	foo[MAP_SZ >> 1] = 0; // Generates SIGBUS with 4.3-rc1
	return 0;
}
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Thread

LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs  have ->vm_ops set") Will Deacon <will.deacon@arm.com> - 2015-09-14 13:00 +0200
  RE: LTP regressions due to 6dc296e7df4c ("mm: make sure all file VMAs  have ->vm_ops set") "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-09-14 14:00 +0200
    Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") Will Deacon <will.deacon@arm.com> - 2015-09-14 15:30 +0200
    Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") Oleg Nesterov <oleg@redhat.com> - 2015-09-14 19:10 +0200
      Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") Oleg Nesterov <oleg@redhat.com> - 2015-09-14 19:50 +0200
      Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-09-14 20:30 +0200
        Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") Oleg Nesterov <oleg@redhat.com> - 2015-09-15 14:20 +0200
          Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-09-15 15:50 +0200
            Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") Oleg Nesterov <oleg@redhat.com> - 2015-09-15 17:20 +0200
            Re: LTP regressions due to 6dc296e7df4c  ("mm: make sure all file VMAs have ->vm_ops set") Andrew Morton <akpm@linux-foundation.org> - 2015-09-16 23:30 +0200
              Re: LTP regressions due to 6dc296e7df4c ("mm: make sure all file  VMAs have ->vm_ops set") "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-09-17 17:40 +0200

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