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

[Caspar Zhang <caspar@casparzhang.com>]

On 04/28/2012 01:15 PM, hejianet wrote:
> 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

Hi, thanks for the patch and sorry for (very very) late response due to
busying other things in past months...

I tried another approach in my PATCH 2/2, it creates a big hole to make
sure 2 3*ps can map successfully. I tried on my systems and it did work.
Could you try my patch 1/2 and 2/2 to see if it can solve your problem?

IIRC, reducing to 1*ps is a solution for this too, yet I've tried to see
if it can reproduce the bug we meet before.

Thanks,
Caspar

> 
> 
> --- 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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