mlock() fix return values

Halesh says:

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 in an mlock() failure with errno 14 that is EFAULT,
but it has nowhere been specified that mlock() will return EFAULT.  When I
tested the same on older kernels 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.

SUSv3 requires the following behavior frmo mlock(2).

[ENOMEM]
    Some or all of the address range specified by the addr and
    len arguments does not correspond to valid mapped pages
    in the address space of the process.

[EAGAIN]
    Some or all of the memory identified by the operation could not
    be locked when the call was made.

This rule isn't so nice and slighly strange.  but many people think
POSIX/SUS compliance is important.

Reported-by: Halesh Sadashiv <halesh.sadashiv@ap.sony.com>
Tested-by: Halesh Sadashiv <halesh.sadashiv@ap.sony.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: <stable@kernel.org>		[2.6.25.x, 2.6.26.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index 6793b9c681074ffb63b3c01765a5cc75aac462ec..a472bcd4b061615504bce67bf93b28cfd723e044 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2765,16 +2765,26 @@ int make_pages_present(unsigned long addr, unsigned long end)
 
        vma = find_vma(current->mm, addr);
        if (!vma)
-               return -1;
+               return -ENOMEM;
        write = (vma->vm_flags & VM_WRITE) != 0;
        BUG_ON(addr >= end);
        BUG_ON(end > vma->vm_end);
        len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
        ret = get_user_pages(current, current->mm, addr,
                        len, write, 0, NULL, NULL);
-       if (ret < 0)
+       if (ret < 0) {
+               /*
+                  SUS require strange return value to mlock
+                   - invalid addr generate to ENOMEM.
+                   - out of memory should generate EAGAIN.
+               */
+               if (ret == -EFAULT)
+                       ret = -ENOMEM;
+               else if (ret == -ENOMEM)
+                       ret = -EAGAIN;
                return ret;
-       return ret == len ? 0 : -1;
+       }
+       return ret == len ? 0 : -ENOMEM;
 }
 
 #if !defined(__HAVE_ARCH_GATE_AREA)

diff --git a/mm/mlock.c b/mm/mlock.c
index 7b2656055d6a96a6b940574e4d23f0a4fc7dd6bc..01fbe93eff5ca25f1143b1295da6ce7115e00bde 100644 (file)
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -78,8 +78,6 @@ success:
 
        mm->locked_vm -= pages;
 out:
-       if (ret == -ENOMEM)
-               ret = -EAGAIN;
        return ret;
 }