Merged in masayuki2009/nuttx.nuttx/fix_smp_bugs (pull request #615)

Fix SMP related bugs

* sched/sched: Fix a deadlock in SMP mode

    Two months ago, I introduced sched_tasklist_lock() and
    sched_tasklist_unlock() to protect tasklists in SMP mode.
    Actually, this change works pretty well for HTTP audio
    streaming aging test with lc823450-xgevk.

    However, I found a deadlock in the scheduler when I tried
    similar aging tests with DVFS autonomous mode where CPU
    clock speed changed based on cpu load. In this case, call
    sequences were as follows;

    cpu1: sched_unlock()->sched_mergepending()->sched_addreadytorun()->up_cpu_pause()
    cpu0: sched_lock()->sched_mergepending()

    To avoid this deadlock, I added sched_tasklist_unlock() when calling
    up_cpu_pause() and sched_addreadytorun(). Also, added
    sched_tasklist_lock() after the call.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

* libc: Add critical section in lib_filesem.c for SMP

    To set my_pid into fs_folder atomically in SMP mode,
    critical section API must be used.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

* mm: Add critical section in mm_sem.c for SMP

    To set my_pid into mm_folder atomically in SMP mode,
    critical section API must be used.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

* net: Add critical section in net_lock.c for SMP

    To set my pid (me) into fs_folder atomically in SMP mode,
    critical section API must be used.

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

Approved-by: Gregory Nutt <gnutt@nuttx.org>