Taskstats fix the structure members alignment issue

Taskstats fix the structure members alignment issue

We broke the the alignment of members of taskstats to the 8 byte boundary
with the CSA patches.  In the current kernel, the taskstats structure is
not suitable for use by 32 bit applications in a 64 bit kernel.

On x86_64

Offsets of taskstats' members (64 bit kernel, 64 bit application)

@taskstats'offsetof[@taskstats'indices] = (
        0,      # version
        4,      # ac_exitcode
        8,      # ac_flag
        9,      # ac_nice
        16,     # cpu_count
        24,     # cpu_delay_total
        32,     # blkio_count
        40,     # blkio_delay_total
        48,     # swapin_count
        56,     # swapin_delay_total
        64,     # cpu_run_real_total
        72,     # cpu_run_virtual_total
        80,     # ac_comm
        112,    # ac_sched
        113,    # ac_pad
        116,    # ac_uid
        120,    # ac_gid
        124,    # ac_pid
        128,    # ac_ppid
        132,    # ac_btime
        136,    # ac_etime
        144,    # ac_utime
        152,    # ac_stime
        160,    # ac_minflt
        168,    # ac_majflt
        176,    # coremem
        184,    # virtmem
        192,    # hiwater_rss
        200,    # hiwater_vm
        208,    # read_char
        216,    # write_char
        224,    # read_syscalls
        232,    # write_syscalls
        240,    # read_bytes
        248,    # write_bytes
        256,    # cancelled_write_bytes
    );

Offsets of taskstats' members (64 bit kernel, 32 bit application)

@taskstats'offsetof[@taskstats'indices] = (
        0,      # version
        4,      # ac_exitcode
        8,      # ac_flag
        9,      # ac_nice
        12,     # cpu_count
        20,     # cpu_delay_total
        28,     # blkio_count
        36,     # blkio_delay_total
        44,     # swapin_count
        52,     # swapin_delay_total
        60,     # cpu_run_real_total
        68,     # cpu_run_virtual_total
        76,     # ac_comm
        108,    # ac_sched
        109,    # ac_pad
        112,    # ac_uid
        116,    # ac_gid
        120,    # ac_pid
        124,    # ac_ppid
        128,    # ac_btime
        132,    # ac_etime
        140,    # ac_utime
        148,    # ac_stime
        156,    # ac_minflt
        164,    # ac_majflt
        172,    # coremem
        180,    # virtmem
        188,    # hiwater_rss
        196,    # hiwater_vm
        204,    # read_char
        212,    # write_char
        220,    # read_syscalls
        228,    # write_syscalls
        236,    # read_bytes
        244,    # write_bytes
        252,    # cancelled_write_bytes
    );

This is one way to solve the problem without re-arranging structure members
is to pack the structure.  The patch adds an __attribute__((aligned(8))) to
the taskstats structure members so that 32 bit applications using taskstats
can work with a 64 bit kernel.

Using __attribute__((packed)) would break the 64 bit alignment of members.

The fix was tested on x86_64. After the fix, we got

Offsets of taskstats' members (64 bit kernel, 64 bit application)

@taskstats'offsetof[@taskstats'indices] = (
        0,      # version
        4,      # ac_exitcode
        8,      # ac_flag
        9,      # ac_nice
        16,     # cpu_count
        24,     # cpu_delay_total
        32,     # blkio_count
        40,     # blkio_delay_total
        48,     # swapin_count
        56,     # swapin_delay_total
        64,     # cpu_run_real_total
        72,     # cpu_run_virtual_total
        80,     # ac_comm
        112,    # ac_sched
        113,    # ac_pad
        120,    # ac_uid
        124,    # ac_gid
        128,    # ac_pid
        132,    # ac_ppid
        136,    # ac_btime
        144,    # ac_etime
        152,    # ac_utime
        160,    # ac_stime
        168,    # ac_minflt
        176,    # ac_majflt
        184,    # coremem
        192,    # virtmem
        200,    # hiwater_rss
        208,    # hiwater_vm
        216,    # read_char
        224,    # write_char
        232,    # read_syscalls
        240,    # write_syscalls
        248,    # read_bytes
        256,    # write_bytes
        264,    # cancelled_write_bytes
    );

Offsets of taskstats' members (64 bit kernel, 32 bit application)

@taskstats'offsetof[@taskstats'indices] = (
        0,      # version
        4,      # ac_exitcode
        8,      # ac_flag
        9,      # ac_nice
        16,     # cpu_count
        24,     # cpu_delay_total
        32,     # blkio_count
        40,     # blkio_delay_total
        48,     # swapin_count
        56,     # swapin_delay_total
        64,     # cpu_run_real_total
        72,     # cpu_run_virtual_total
        80,     # ac_comm
        112,    # ac_sched
        113,    # ac_pad
        120,    # ac_uid
        124,    # ac_gid
        128,    # ac_pid
        132,    # ac_ppid
        136,    # ac_btime
        144,    # ac_etime
        152,    # ac_utime
        160,    # ac_stime
        168,    # ac_minflt
        176,    # ac_majflt
        184,    # coremem
        192,    # virtmem
        200,    # hiwater_rss
        208,    # hiwater_vm
        216,    # read_char
        224,    # write_char
        232,    # read_syscalls
        240,    # write_syscalls
        248,    # read_bytes
        256,    # write_bytes
        264,    # cancelled_write_bytes
    );

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Jay Lan <jlan@engr.sgi.com>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>