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To: linux-kernel@vger.kernel.org
From: Halesh <halesh.s@india.com>
Subject: mlock() return value issue in kernel 2.6.23.17
Date: Thu, 31 Jul 2008 10:15:10 +0000 (UTC)
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Hi all,

Please find the below testcase provide to test mlock.

Test Case :
===========================

#include <sys/resource.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>

int main(void)
{
  int fd,ret, i = 0;
  char *addr, *addr1 = NULL;
  unsigned int page_size;
  struct rlimit rlim;

  if (0 != geteuid()) 
  {
   printf("Execute this pgm as root\n");
   exit(1);
  }

  /* create a file */
  if ((fd = open("mmap_test.c",O_RDWR|O_CREAT,0755)) == -1)
  {
   printf("cant create test file\n");
   exit(1);
  }

  page_size = sysconf(_SC_PAGE_SIZE);

  /* set the MEMLOCK limit */
  rlim.rlim_cur = 2000;
  rlim.rlim_max = 2000;

  if ((ret = setrlimit(RLIMIT_MEMLOCK,&rlim)) != 0)
  {
   printf("Cant change limit values\n");
   exit(1);
  }

  addr = 0;
  while (1)
  {
  /* map a page into memory each time*/ 
  if ((addr = (char *) mmap(addr,page_size, PROT_READ |     
PROT_WRITE,MAP_SHARED,fd,0)) == MAP_FAILED) 
  {
   printf("cant do mmap on file\n");
   exit(1);
  }

  if (0 == i)
    addr1 = addr;
  i++;
  errno = 0;	
  /* lock the mapped memory pagewise*/
  if ((ret = mlock((char *)addr, 1500)) == -1) 
  {
   printf("errno value is %d\n", errno);
   printf("cant lock maped region\n");
   exit(1);
  }
  addr = addr + page_size;
 }
}
======================================================


This testcase results with mlock failure with errno 14 that is EFAULT, but this 
has been no where reported that mlock will give EFAULT, When i tested the same 
on older kernel like 2.6.18, I got the correct result i.e errno 12 (ENOMEM).


I think in source code mlock(2),  setting errno ENOMEM has been missed in 
do_mlock() , on mlock_fixup() failure.

Let me know if my understanding is wrong!

Thanks,
Halesh