[LTP] [PATCH]page numbers should be decreased to 1 in vma01 test

[hejianet <hejianet@linux.vnet.ibm.com>]

Hi all
testcases/kernel/mem/vma/vma01.c is to test the result of
find_mergeable_anon_vma()
In my opinion, it is not correct in some architectures
1)some architectures(eg.ppcnf) use *bottomup* vma layout instead of
*topdown*
so vma01 test should be masked in those architectures.

2)even in the *topdown* architectures, there is a potential issure.
I will give an example to show why the pagesize should be decreased from
3 to 1
a.out is an elf file compiled from vma01.c with minor revision.
>-bash-4.1# strace -f ./a.out
>execve("./a.out", ["./a.out"], [/* 22 vars */]) = 0
>brk(0)                                  = 0x10012000
>mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x47ffd000
>access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or
directory)
>open("/etc/ld.so.cache", O_RDONLY)      = 3
>fstat64(3, {st_mode=S_IFREG|0644, st_size=12875, ...}) = 0
>mmap(NULL, 12875, PROT_READ, MAP_PRIVATE, 3, 0) = 0x47ff9000
>close(3)                                = 0
>open("/lib/libc.so.6", O_RDONLY)        = 3
>read(3,
"\177ELF\1\2\1\0\0\0\0\0\0\0\0\0\0\3\0\24\0\0\0\1\0\1\351\354\0\0\0004"...,
512) = 512
>fstat64(3, {st_mode=S_IFREG|0755, st_size=2015420, ...}) = 0
>mmap(0xfe2c000, 1848788, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xfe2c000
>mprotect(0xffd2000, 90112, PROT_NONE)   = 0
>mmap(0xffe8000, 20480, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1ac000) = 0xffe8000
>mmap(0xffed000, 9684, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xffed000
>close(3)                                = 0
>mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x47ff8000
>mprotect(0xffe8000, 16384, PROT_READ)   = 0
>mprotect(0x47ffe000, 4096, PROT_READ)   = 0
>munmap(0x47ff9000, 12875)               = 0
>mmap(NULL, 12288, PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0) = 0x47ffa000
>clone(Process 698 attached
>child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x47ff8068) = 698
>[pid   697] waitpid(-1,  <unfinished ...>
>[pid   698] mmap(0x47ffd000, 12288, PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, 0, 0) = 0x47ff5000
>[pid   698] fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0),
...}) = 0
>[pid   698] mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x47ff9000
>[pid   698] write(1, "parent: t = 0x47ffa000\n", 23parent: t = 0x47ffa000
>) = 23

the symptom is when /etc/ld.so.cache is small, we never get a 2 3*ps
aligned pages.
we got the layout like this:
...
3*ps by children
1*ps
1*ps
3*ps by parent
...
summary: a) the mmap area for loading /etc/ld.so.cache is nearby the
normal mmap()
         b) if the /etc/ld.so.cache is small, when it is unmmaped, there
is a small hole left for allocating later.
         c) we couldn't make sure that the 3*ps will be alignedly
allocated if /etc/ld.so.cache is so small

conclusion: we need decrease the page number from 3 to 1 in vma01 test


--- testcases/kernel/mem/vma/vma01.c.ori    2012-04-28
12:51:16.453125000 +0800
+++ testcases/kernel/mem/vma/vma01.c    2012-04-28 12:53:35.375000000 +0800
@@ -92,7 +92,7 @@ static void check_vma(void)
     int status;
     void *t, *u, *x, *y;
 
-    t = mmap(NULL, 3*ps, PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
+    t = mmap(NULL, 1*ps, PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
     if (t == MAP_FAILED)
         tst_brkm(TBROK|TERRNO, cleanup, "mmap");
     memset(t, 1, ps);
@@ -102,7 +102,7 @@ static void check_vma(void)
         tst_brkm(TBROK|TERRNO, cleanup, "fork");
     case 0:
         memset(t, 2, ps);
-        u = mmap(t + 3*ps, 3*ps, PROT_WRITE,
+        u = mmap(t + 1*ps, 1*ps, PROT_WRITE,
                 MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
         if (u == MAP_FAILED) {
             perror("mmap failed.\n");
@@ -113,11 +113,11 @@ static void check_vma(void)
         memset(u, 2, ps);
 
         x = get_end_addr(u, MAPS_FILE);
-        if (x == u + 6*ps)
+        if (x == u + 2*ps)
             exit(1);
-        if (x == u + 3*ps) {
+        if (x == u + 1*ps) {
             y = get_end_addr(x, MAPS_FILE);
-            if (y == x + 3*ps)
+            if (y == x + 1*ps)
                 exit(0);
         }
         exit(255);
@@ -157,10 +157,10 @@ static void check_status(int status)
 {
     switch (status) {
     case 0:
-        tst_resm(TPASS, "two 3*ps VMAs found.");
+        tst_resm(TPASS, "two 1*ps VMAs found.");
         break;
     case 1:
-        tst_resm(TFAIL, "A single 6*ps VMA found.");
+        tst_resm(TFAIL, "A single 2*ps VMA found.");
         break;
     default:
         tst_brkm(TBROK, cleanup, "unexpected VMA found.");



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