mm: vmscan: clear kswapd's special reclaim powers before exiting

When kswapd exits, it can end up taking locks that were previously held
by allocating tasks while they waited for reclaim.  Lockdep currently
warns about this:

On Wed, May 28, 2014 at 06:06:34PM +0800, Gu Zheng wrote:
>  inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.
>  kswapd2/1151 [HC0[0]:SC0[0]:HE1:SE1] takes:
>   (&sig->group_rwsem){+++++?}, at: exit_signals+0x24/0x130
>  {RECLAIM_FS-ON-W} state was registered at:
>     mark_held_locks+0xb9/0x140
>     lockdep_trace_alloc+0x7a/0xe0
>     kmem_cache_alloc_trace+0x37/0x240
>     flex_array_alloc+0x99/0x1a0
>     cgroup_attach_task+0x63/0x430
>     attach_task_by_pid+0x210/0x280
>     cgroup_procs_write+0x16/0x20
>     cgroup_file_write+0x120/0x2c0
>     vfs_write+0xc0/0x1f0
>     SyS_write+0x4c/0xa0
>     tracesys+0xdd/0xe2
>  irq event stamp: 49
>  hardirqs last  enabled at (49):  _raw_spin_unlock_irqrestore+0x36/0x70
>  hardirqs last disabled at (48):  _raw_spin_lock_irqsave+0x2b/0xa0
>  softirqs last  enabled at (0):  copy_process.part.24+0x627/0x15f0
>  softirqs last disabled at (0):            (null)
>
>  other info that might help us debug this:
>   Possible unsafe locking scenario:
>
>         CPU0
>         ----
>    lock(&sig->group_rwsem);
>    <Interrupt>
>      lock(&sig->group_rwsem);
>
>   *** DEADLOCK ***
>
>  no locks held by kswapd2/1151.
>
>  stack backtrace:
>  CPU: 30 PID: 1151 Comm: kswapd2 Not tainted 3.10.39+ #4
>  Call Trace:
>    dump_stack+0x19/0x1b
>    print_usage_bug+0x1f7/0x208
>    mark_lock+0x21d/0x2a0
>    __lock_acquire+0x52a/0xb60
>    lock_acquire+0xa2/0x140
>    down_read+0x51/0xa0
>    exit_signals+0x24/0x130
>    do_exit+0xb5/0xa50
>    kthread+0xdb/0x100
>    ret_from_fork+0x7c/0xb0

This is because the kswapd thread is still marked as a reclaimer at the
time of exit.  But because it is exiting, nobody is actually waiting on
it to make reclaim progress anymore, and it's nothing but a regular
thread at this point.  Be tidy and strip it of all its powers
(PF_MEMALLOC, PF_SWAPWRITE, PF_KSWAPD, and the lockdep reclaim state)
before returning from the thread function.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memory-failure.c-failure: send right signal code to correct thread

When a thread in a multi-threaded application hits a machine check because
of an uncorrectable error in memory - we want to send the SIGBUS with
si.si_code = BUS_MCEERR_AR to that thread.  Currently we fail to do that
if the active thread is not the primary thread in the process.
collect_procs() just finds primary threads and this test:

	if ((flags & MF_ACTION_REQUIRED) && t == current) {

will see that the thread we found isn't the current thread and so send a
si.si_code = BUS_MCEERR_AO to the primary (and nothing to the active
thread at this time).

We can fix this by checking whether "current" shares the same mm with the
process that collect_procs() said owned the page.  If so, we send the
SIGBUS to current (with code BUS_MCEERR_AR).

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reported-by: Otto Bruggeman <otto.g.bruggeman@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Chen Gong <gong.chen@linux.jf.intel.com>
Cc: <stable@vger.kernel.org>	[3.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memory-failure.c: don't let collect_procs() skip over processes for MF_ACTION_REQUIRED

When Linux sees an "action optional" machine check (where h/w has reported
an error that is not in the current execution path) we generally do not
want to signal a process, since most processes do not have a SIGBUS
handler - we'd just prematurely terminate the process for a problem that
they might never actually see.

task_early_kill() decides whether to consider a process - and it checks
whether this specific process has been marked for early signals with
"prctl", or if the system administrator has requested early signals for
all processes using /proc/sys/vm/memory_failure_early_kill.

But for MF_ACTION_REQUIRED case we must not defer.  The error is in the
execution path of the current thread so we must send the SIGBUS
immediatley.

Fix by passing a flag argument through collect_procs*() to
task_early_kill() so it knows whether we can defer or must take action.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Chen Gong <gong.chen@linux.jf.intel.com>
Cc: <stable@vger.kernel.org>	[3.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>