• Kirill A. Shutemov's avatar
    mm: fix regression in remap_file_pages() emulation · 48f7df32
    Kirill A. Shutemov authored
    Grazvydas Ignotas has reported a regression in remap_file_pages()
    emulation.
    
    Testcase:
    	#define _GNU_SOURCE
    	#include <assert.h>
    	#include <stdlib.h>
    	#include <stdio.h>
    	#include <sys/mman.h>
    
    	#define SIZE    (4096 * 3)
    
    	int main(int argc, char **argv)
    	{
    		unsigned long *p;
    		long i;
    
    		p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
    				MAP_SHARED | MAP_ANONYMOUS, -1, 0);
    		if (p == MAP_FAILED) {
    			perror("mmap");
    			return -1;
    		}
    
    		for (i = 0; i < SIZE / 4096; i++)
    			p[i * 4096 / sizeof(*p)] = i;
    
    		if (remap_file_pages(p, 4096, 0, 1, 0)) {
    			perror("remap_file_pages");
    			return -1;
    		}
    
    		if (remap_file_pages(p, 4096 * 2, 0, 1, 0)) {
    			perror("remap_file_pages");
    			return -1;
    		}
    
    		assert(p[0] == 1);
    
    		munmap(p, SIZE);
    
    		return 0;
    	}
    
    The second remap_file_pages() fails with -EINVAL.
    
    The reason is that remap_file_pages() emulation assumes that the target
    vma covers whole area we want to over map.  That assumption is broken by
    first remap_file_pages() call: it split the area into two vma.
    
    The solution is to check next adjacent vmas, if they map the same file
    with the same flags.
    
    Fixes: c8d78c18 ("mm: replace remap_file_pages() syscall with emulation")
    Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Reported-by: default avatarGrazvydas Ignotas <notasas@gmail.com>
    Tested-by: default avatarGrazvydas Ignotas <notasas@gmail.com>
    Cc: <stable@vger.kernel.org>	[4.0+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    48f7df32
mmap.c 91.9 KB