From: Michal Hocko <mhocko@kernel.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
dave.hansen@intel.com, ak@linux.intel.com, aaron.lu@intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Hugh Dickins <hughd@google.com>, Shaohua Li <shli@kernel.org>,
Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Hillf Danton <hillf.zj@alibaba-inc.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH v5 0/9] mm/swap: Regular page swap optimizations
Date: Tue, 17 Jan 2017 08:49:39 +0100 [thread overview]
Message-ID: <20170117074939.GA19699@dhcp22.suse.cz> (raw)
In-Reply-To: <878tqapkar.fsf@yhuang-dev.intel.com>
On Tue 17-01-17 09:06:04, Huang, Ying wrote:
> Michal Hocko <mhocko@kernel.org> writes:
>
> > Hi,
> > I am seeing a lot of preempt unsafe warnings with the current mmotm and
> > I assume that this patchset has introduced the issue. I haven't checked
> > more closely but get_swap_page didn't use this_cpu_ptr before "mm/swap:
> > add cache for swap slots allocation"
> >
> > [ 57.812314] BUG: using smp_processor_id() in preemptible [00000000] code: kswapd0/527
> > [ 57.814360] caller is debug_smp_processor_id+0x17/0x19
> > [ 57.815237] CPU: 1 PID: 527 Comm: kswapd0 Tainted: G W 4.9.0-mmotm-00135-g4e9a9895ebef #1042
> > [ 57.816019] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1 04/01/2014
> > [ 57.816019] ffffc900001939c0 ffffffff81329c60 0000000000000001 ffffffff81a0ce06
> > [ 57.816019] ffffc900001939f0 ffffffff81343c2a 00000000000137a0 ffffea0000dfd2a0
> > [ 57.816019] ffff88003c49a700 ffffc90000193b10 ffffc90000193a00 ffffffff81343c53
> > [ 57.816019] Call Trace:
> > [ 57.816019] [<ffffffff81329c60>] dump_stack+0x68/0x92
> > [ 57.816019] [<ffffffff81343c2a>] check_preemption_disabled+0xce/0xe0
> > [ 57.816019] [<ffffffff81343c53>] debug_smp_processor_id+0x17/0x19
> > [ 57.816019] [<ffffffff8115f06f>] get_swap_page+0x19/0x183
> > [ 57.816019] [<ffffffff8114e01d>] shmem_writepage+0xce/0x38c
> > [ 57.816019] [<ffffffff81148916>] shrink_page_list+0x81f/0xdbf
> > [ 57.816019] [<ffffffff81149652>] shrink_inactive_list+0x2ab/0x594
> > [ 57.816019] [<ffffffff8114a22f>] shrink_node_memcg+0x4c7/0x673
> > [ 57.816019] [<ffffffff8114a49f>] shrink_node+0xc4/0x282
> > [ 57.816019] [<ffffffff8114a49f>] ? shrink_node+0xc4/0x282
> > [ 57.816019] [<ffffffff8114b8cb>] kswapd+0x656/0x834
> > [ 57.816019] [<ffffffff8114b275>] ? mem_cgroup_shrink_node+0x2e1/0x2e1
> > [ 57.816019] [<ffffffff81069fb4>] ? call_usermodehelper_exec_async+0x124/0x12d
> > [ 57.816019] [<ffffffff81073621>] kthread+0xf9/0x101
> > [ 57.816019] [<ffffffff81660198>] ? _raw_spin_unlock_irq+0x2c/0x4a
> > [ 57.816019] [<ffffffff81073528>] ? kthread_park+0x5a/0x5a
> > [ 57.816019] [<ffffffff81069e90>] ? umh_complete+0x25/0x25
> > [ 57.816019] [<ffffffff81660b07>] ret_from_fork+0x27/0x40
>
> Sorry for bothering, we should have tested this before.
I am always running my tests with CONFIG_DEBUG_PREEMPT=y which is what
has caught this one.
[...]
> > would be a way to go but the function takes a sleeping lock so disabling
> > the preemption is not a way forward. So this is either preempt safe
> > for some reason - which should be IMHO documented in a comment - and
> > raw_cpu_ptr can be used or this needs a deeper thought.
>
> Thanks for pointing out this.
>
> We think this is preempt safe. During the development, we have
> considered the possible preemption between getting the per-CPU pointer
> and its usage, and implemented the code to make it work at that
> situation. We will change the code to use raw_cpu_ptr() and add a
> comment for it.
FWIW s@this_cpu_ptr@raw_cpu_ptr@ which I am using as a workaround now
hasn't seemed to cause any issue. At least nothing observable like a
crash.
Thanks!
--
Michal Hocko
SUSE Labs
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prev parent reply other threads:[~2017-01-17 7:49 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-11 17:55 [PATCH v5 0/9] mm/swap: Regular page swap optimizations Tim Chen
2017-01-11 17:55 ` [PATCH v5 1/9] mm/swap: Fix kernel message in swap_info_get() Tim Chen
2017-01-11 17:55 ` [PATCH v5 2/9] mm/swap: Add cluster lock Tim Chen
2017-01-11 23:00 ` Andrew Morton
2017-01-11 23:07 ` Jonathan Corbet
2017-01-11 23:15 ` Andrew Morton
2017-01-12 1:47 ` Huang, Ying
2017-01-12 1:58 ` Andrew Morton
2017-01-12 2:51 ` Huang, Ying
2017-01-14 4:37 ` [Update][PATCH " Huang, Ying
2017-01-12 1:23 ` [PATCH " Huang, Ying
2017-01-11 17:55 ` [PATCH v5 3/9] mm/swap: Split swap cache into 64MB trunks Tim Chen
2017-01-11 23:09 ` Andrew Morton
2017-01-11 23:19 ` Andi Kleen
2017-01-12 16:47 ` Tim Chen
2017-01-11 17:55 ` [PATCH v5 4/9] mm/swap: skip read ahead for unreferenced swap slots Tim Chen
2017-01-11 17:55 ` [PATCH v5 5/9] mm/swap: Allocate swap slots in batches Tim Chen
2017-01-11 17:55 ` [PATCH v5 6/9] mm/swap: Free swap slots in batch Tim Chen
2017-01-11 17:55 ` [PATCH v5 7/9] mm/swap: Add cache for swap slots allocation Tim Chen
2017-01-17 2:55 ` [Update][PATCH " Huang, Ying
2017-01-17 10:16 ` Michal Hocko
2017-01-17 17:24 ` Chen, Tim C
2017-01-17 20:03 ` Michal Hocko
2017-01-17 20:31 ` Chen, Tim C
2017-01-17 21:42 ` Tim Chen
2017-01-18 12:45 ` Michal Hocko
2017-01-18 18:03 ` Tim Chen
2017-01-18 18:15 ` Michal Hocko
2017-01-11 17:55 ` [PATCH v5 8/9] mm/swap: Enable swap slots cache usage Tim Chen
2017-01-11 17:55 ` [PATCH v5 9/9] mm/swap: Skip readahead only when swap slot cache is enabled Tim Chen
2017-01-16 12:02 ` [PATCH v5 0/9] mm/swap: Regular page swap optimizations Michal Hocko
2017-01-17 1:06 ` Huang, Ying
2017-01-17 7:49 ` Michal Hocko [this message]
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