[PATCH -next] slub: Replace __this_cpu_inc usage w/ SLUB_STATS

Josh Cartwright
2014-03-06T18:32:33Z

On Thu, Mar 06, 2014 at 09:53:16AM -0600, Josh Cartwright wrote:
> Booting on my Samsung Series 9 laptop gives me loads and loads of BUGs
> triggered by __this_cpu_add(), making making the system completely
> unusable:
>
> [ 5.808326] BUG: using __this_cpu_add() in preemptible [00000000] code: swapper/0/1
> [ 5.812331] caller is __this_cpu_preempt_check+0x2b/0x30
> [ 5.815654] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.14.0-rc5-next-20140306-joshc-08290-g0ffb2fe #1
> [ 5.819553] Hardware name: SAMSUNG ELECTRONICS CO., LTD. 900X3C/900X3D/900X3E/900X4C/900X4D/NP900X3E-A02US, BIOS P07ABK 04/09/2013
> [ 5.823558] ffff8801182157c0 ffff880118215790 ffffffff81a64cec 0000000000000000
> [ 5.827177] ffff8801182157b0 ffffffff81462360 ffff8800c3d553e0 ffffea00030f5500
> [ 5.830744] ffff8801182157e8 ffffffff814623bb 635f736968745f5f 29286464615f7570
> [ 5.834134] Call Trace:
> [ 5.836848] [<ffffffff81a64cec>] dump_stack+0x4e/0x7a
> [ 5.839943] [<ffffffff81462360>] check_preemption_disabled+0xd0/0xe0
> [ 5.842997] [<ffffffff814623bb>] __this_cpu_preempt_check+0x2b/0x30
> [ 5.846022] [<ffffffff81a6331d>] __slab_free+0x38/0x590
> [ 5.848863] [<ffffffff811759dd>] ? get_parent_ip+0xd/0x50
> [ 5.850467] BUG: using __this_cpu_add() in preemptible [00000000] code: khubd/36
> [ 5.850472] caller is __this_cpu_preempt_check+0x2b/0x30
> [ 5.859125] [<ffffffff81175b3b>] ? preempt_count_sub+0x6b/0xf0
> [ 5.862521] [<ffffffff81a7175a>] ? _raw_spin_unlock_irqrestore+0x4a/0x80
> [ 5.865599] [<ffffffff81462e5e>] ? __debug_check_no_obj_freed+0x13e/0x240
> [ 5.868738] [<ffffffff814623bb>] ? __this_cpu_preempt_check+0x2b/0x30
> [ 5.871799] [<ffffffff81287327>] kfree+0x2f7/0x300

FWIW, it looks like the magic combination of options are:
- CONFIG_DEBUG_PREEMPT=y
- CONFIG_SLUB=y
- CONFIG_SLUB_STATS=y

Looks like the new percpu() checks are complaining about SLUB's use of
__this_cpu_inc() for maintaining it's stat counters. The below patch
seems to fix it.

Although, I'm wondering how exact these statistics need to be. Is
making them preemption safe even a concern?

Thanks,
Josh

--8<--
Make slub statistics maintenance preemption-safe.

Fixes the following warning when CONFIG_SLUB_STATS and
CONFIG_DEBUG_PREEMPT:

BUG: using __this_cpu_add() in preemptible [00000000] code: systemd-journal/226
caller is __this_cpu_preempt_check+0x2b/0x30
Call Trace:
dump_stack+0x4e/0x7a
check_preemption_disabled+0xd0/0xe0
__this_cpu_preempt_check+0x2b/0x30
__slab_free+0x38/0x590
kmem_cache_free+0x367/0x3a0
jbd2_journal_stop+0x24d/0x500
__ext4_journal_stop+0x37/0x90
ext4_truncate+0x1ab/0x570
ext4_setattr+0x2d3/0x810
notify_change+0x159/0x3a0
do_truncate+0x6f/0xa0
do_sys_ftruncate.constprop.18+0x10e/0x160
SyS_ftruncate+0xe/0x10
system_call_fastpath+0x1a/0x1f

Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
---
mm/slub.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index c6eb29d..c873e61 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -224,7 +224,7 @@ static inline void memcg_propagate_slab_attrs(struct kmem_cache *s) { }
static inline void stat(const struct kmem_cache *s, enum stat_item si)
{
#ifdef CONFIG_SLUB_STATS
- __this_cpu_inc(s->cpu_slab->stat[si]);
+ this_cpu_inc(s->cpu_slab->stat[si]);
#endif
}

--
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