Patch "mm: vmscan: clear kswapd's special reclaim powers before exiting" has been added to the 3.15-stable tree

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This is a note to let you know that I've just added the patch titled

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

to the 3.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-vmscan-clear-kswapd-s-special-reclaim-powers-before-exiting.patch
and it can be found in the queue-3.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 71abdc15adf8c702a1dd535f8e30df50758848d2 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Date: Fri, 6 Jun 2014 14:35:35 -0700
Subject: mm: vmscan: clear kswapd's special reclaim powers before exiting

From: Johannes Weiner <hannes@xxxxxxxxxxx>

commit 71abdc15adf8c702a1dd535f8e30df50758848d2 upstream.

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@xxxxxxxxxxx>
Reported-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: Tang Chen <tangchen@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/vmscan.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3333,7 +3333,10 @@ static int kswapd(void *p)
 		}
 	}
 
+	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
 	current->reclaim_state = NULL;
+	lockdep_clear_current_reclaim_state();
+
 	return 0;
 }
 


Patches currently in stable-queue which might be from hannes@xxxxxxxxxxx are

queue-3.15/memcg-do-not-hang-on-oom-when-killed-by-userspace-oom-access-to-memory-reserves.patch
queue-3.15/mm-page_alloc-use-word-based-accesses-for-get-set-pageblock-bitmaps.patch
queue-3.15/mm-vmscan-clear-kswapd-s-special-reclaim-powers-before-exiting.patch
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