Re: [PATCH 6/7] mm: add CONFIG_DEBUG_VM_RB build option

From: Sasha Levin
Date: Fri Sep 14 2012 - 18:13:38 EST


On 09/04/2012 11:20 AM, Michel Lespinasse wrote:
> Add a CONFIG_DEBUG_VM_RB build option for the previously existing
> DEBUG_MM_RB code. Now that Andi Kleen modified it to avoid using
> recursive algorithms, we can expose it a bit more.
>
> Also extend this code to validate_mm() after stack expansion, and to
> check that the vma's start and last pgoffs have not changed since the
> nodes were inserted on the anon vma interval tree (as it is important
> that the nodes be reindexed after each such update).

This patch exposes the following warning:

[ 24.977502] ------------[ cut here ]------------
[ 24.979089] WARNING: at mm/interval_tree.c:110
anon_vma_interval_tree_verify+0x81/0xa0()
[ 24.981765] Pid: 5928, comm: trinity-child37 Tainted: G W
3.6.0-rc5-next-20120914-sasha-00003-g7deb7fa-dirty #333
[ 24.985501] Call Trace:
[ 24.986345] [<ffffffff81224c91>] ? anon_vma_interval_tree_verify+0x81/0xa0
[ 24.988535] [<ffffffff81106766>] warn_slowpath_common+0x86/0xb0
[ 24.990636] [<ffffffff81106855>] warn_slowpath_null+0x15/0x20
[ 24.992658] [<ffffffff81224c91>] anon_vma_interval_tree_verify+0x81/0xa0
[ 24.994980] [<ffffffff8122e6e8>] validate_mm+0x58/0x1e0
[ 24.996772] [<ffffffff8122e934>] vma_link+0x94/0xe0
[ 24.997719] [<ffffffff812315e9>] copy_vma+0x279/0x2e0
[ 24.998522] [<ffffffff8117a7fd>] ? trace_hardirqs_off+0xd/0x10
[ 25.000772] [<ffffffff81232e89>] move_vma+0xa9/0x260
[ 25.002499] [<ffffffff812334b5>] sys_mremap+0x475/0x540
[ 25.004364] [<ffffffff8374b6e8>] tracesys+0xe1/0xe6
[ 25.006108] ---[ end trace 7c901670963aa6e2 ]---

The code line is

WARN_ON_ONCE(node->cached_vma_last != avc_last_pgoff(node));
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