linux-kernel - Re: [PATCH] mm: Remove bogus warning in copy_huge

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Message-ID: <52B33C93.2020006@redhat.com>
Date:	Thu, 19 Dec 2013 13:36:03 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Alex Thorlton <athorlton@....com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Remove bogus warning in copy_huge_pmd

On 12/19/2013 07:00 AM, Mel Gorman wrote:
> Sasha Levin reported the following warning being triggered
>
> [ 1704.594807] WARNING: CPU: 28 PID: 35287 at mm/huge_memory.c:887 copy_huge_pmd+0x145/ 0x3a0()
> [ 1704.597258] Modules linked in:
> [ 1704.597844] CPU: 28 PID: 35287 Comm: trinity-main Tainted: G        W    3.13.0-rc4-next-20131217-sasha-00013-ga878504-dirty #4149
> [ 1704.599924]  0000000000000377e delta! pid slot 27 [36258]: old:2 now:537927697 diff: 537927695 ffff8803593ddb90 ffffffff8439501c ffffffff854722c1
> [ 1704.604846]  0000000000000000 ffff8803593ddbd0 ffffffff8112f8ac ffff8803593ddbe0
> [ 1704.606391]  ffff88034bc137f0 ffff880e41677000 8000000b47c009e4 ffff88034a638000
> [ 1704.608008] Call Trace:
> [ 1704.608511]  [<ffffffff8439501c>] dump_stack+0x52/0x7f
> [ 1704.609699]  [<ffffffff8112f8ac>] warn_slowpath_common+0x8c/0xc0
> [ 1704.612617]  [<ffffffff8112f8fa>] warn_slowpath_null+0x1a/0x20
> [ 1704.614043]  [<ffffffff812b91c5>] copy_huge_pmd+0x145/0x3a0
> [ 1704.615587]  [<ffffffff8127e032>] copy_page_range+0x3f2/0x560
> [ 1704.616869]  [<ffffffff81199ef1>] ? rwsem_wake+0x51/0x70
> [ 1704.617942]  [<ffffffff8112cf59>] dup_mmap+0x2c9/0x3d0
> [ 1704.619146]  [<ffffffff8112d54d>] dup_mm+0xad/0x150
> [ 1704.620051]  [<ffffffff8112e178>] copy_process+0xa68/0x12e0
> [ 1704.622976]  [<ffffffff81194eda>] ? __lock_release+0x1da/0x1f0
> [ 1704.624234]  [<ffffffff8112eee6>] do_fork+0x96/0x270
> [ 1704.624975]  [<ffffffff81249465>] ? context_tracking_user_exit+0x195/0x1d0
> [ 1704.626427]  [<ffffffff811930ed>] ? trace_hardirqs_on+0xd/0x10
> [ 1704.627681]  [<ffffffff8112f0d6>] SyS_clone+0x16/0x20
> [ 1704.628833]  [<ffffffff843a6309>] stub_clone+0x69/0x90
> [ 1704.629672]  [<ffffffff843a6150>] ? tracesys+0xdd/0xe2
>
> This warning was introduced by "mm: numa: Avoid unnecessary disruption
> of NUMA hinting during migration" for paranoia reasons but the warning
> is bogus. I was thinking of parallel races between NUMA hinting faults
> and forks but this warning would also be triggered by a parallel reclaim
> splitting a THP during a fork. Remote the bogus warning.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Acked-by: Rik van Riel <riel@...hat.com>

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