From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: 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:
> [ 2457.683370] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.
> [ 2457.761540] kswapd2/1151 [HC0[0]:SC0[0]:HE1:SE1] takes:
> [ 2457.824102] (&sig->group_rwsem){+++++?}, at: [<ffffffff81071864>] exit_signals+0x24/0x130
> [ 2457.923538] {RECLAIM_FS-ON-W} state was registered at:
> [ 2457.985055] [<ffffffff810bfc99>] mark_held_locks+0xb9/0x140
> [ 2458.053976] [<ffffffff810c1e3a>] lockdep_trace_alloc+0x7a/0xe0
> [ 2458.126015] [<ffffffff81194f47>] kmem_cache_alloc_trace+0x37/0x240
> [ 2458.202214] [<ffffffff812c6e89>] flex_array_alloc+0x99/0x1a0
> [ 2458.272175] [<ffffffff810da563>] cgroup_attach_task+0x63/0x430
> [ 2458.344214] [<ffffffff810dcca0>] attach_task_by_pid+0x210/0x280
> [ 2458.417294] [<ffffffff810dcd26>] cgroup_procs_write+0x16/0x20
> [ 2458.488287] [<ffffffff810d8410>] cgroup_file_write+0x120/0x2c0
> [ 2458.560320] [<ffffffff811b21a0>] vfs_write+0xc0/0x1f0
> [ 2458.622994] [<ffffffff811b2bac>] SyS_write+0x4c/0xa0
> [ 2458.684618] [<ffffffff815ec3c0>] tracesys+0xdd/0xe2
> [ 2458.745214] irq event stamp: 49
> [ 2458.782794] hardirqs last enabled at (49): [<ffffffff815e2b56>] _raw_spin_unlock_irqrestore+0x36/0x70
> [ 2458.894388] hardirqs last disabled at (48): [<ffffffff815e337b>] _raw_spin_lock_irqsave+0x2b/0xa0
> [ 2459.000771] softirqs last enabled at (0): [<ffffffff81059247>] copy_process.part.24+0x627/0x15f0
> [ 2459.107161] softirqs last disabled at (0): [< (null)>] (null)
> [ 2459.195852]
> [ 2459.195852] other info that might help us debug this:
> [ 2459.274024] Possible unsafe locking scenario:
> [ 2459.274024]
> [ 2459.344911] CPU0
> [ 2459.374161] ----
> [ 2459.403408] lock(&sig->group_rwsem);
> [ 2459.448490] <Interrupt>
> [ 2459.479825] lock(&sig->group_rwsem);
> [ 2459.526979]
> [ 2459.526979] *** DEADLOCK ***
> [ 2459.526979]
> [ 2459.597866] no locks held by kswapd2/1151.
> [ 2459.646896]
> [ 2459.646896] stack backtrace:
> [ 2459.699049] CPU: 30 PID: 1151 Comm: kswapd2 Not tainted 3.10.39+ #4
> [ 2459.774098] Hardware name: FUJITSU PRIMEQUEST2800E/SB, BIOS PRIMEQUEST 2000 Series BIOS Version 01.48 05/07/2014
> [ 2459.895983] ffffffff82284bf0 ffff88085856bbf8 ffffffff815dbcf6 ffff88085856bc48
> [ 2459.985003] ffffffff815d67c6 0000000000000000 ffff880800000001 ffff880800000001
> [ 2460.074024] 000000000000000a ffff88085edc9600 ffffffff810be0e0 0000000000000009
> [ 2460.163087] Call Trace:
> [ 2460.192345] [<ffffffff815dbcf6>] dump_stack+0x19/0x1b
> [ 2460.253874] [<ffffffff815d67c6>] print_usage_bug+0x1f7/0x208
> [ 2460.399807] [<ffffffff810bfb5d>] mark_lock+0x21d/0x2a0
> [ 2460.462369] [<ffffffff810c076a>] __lock_acquire+0x52a/0xb60
> [ 2460.735516] [<ffffffff810c1592>] lock_acquire+0xa2/0x140
> [ 2460.935691] [<ffffffff815e01e1>] down_read+0x51/0xa0
> [ 2461.062888] [<ffffffff81071864>] exit_signals+0x24/0x130
> [ 2461.127536] [<ffffffff81060d55>] do_exit+0xb5/0xa50
> [ 2461.320433] [<ffffffff8108303b>] kthread+0xdb/0x100
> [ 2461.532049] [<ffffffff815ec0ec>] 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>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN mm/vmscan.c~mm-vmscan-clear-kswapds-special-reclaim-powers-before-exiting mm/vmscan.c
--- a/mm/vmscan.c~mm-vmscan-clear-kswapds-special-reclaim-powers-before-exiting
+++ a/mm/vmscan.c
@@ -3372,7 +3372,10 @@ static int kswapd(void *p)
}
}
+ tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
current->reclaim_state = NULL;
+ lockdep_clear_current_reclaim_state();
+
return 0;
}
_
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