Messages in this thread Patch in this message | | | Date | Tue, 17 Jan 2017 13:42:35 -0800 | From | Tim Chen <> | Subject | Re: [Update][PATCH v5 7/9] mm/swap: Add cache for swap slots allocation |
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On Tue, Jan 17, 2017 at 10:55:47AM +0800, Huang, Ying wrote: > Hi, Andrew, > > This update patch is to fix the preemption warning raised by Michal > Hocko. raw_cpu_ptr() is used to replace this_cpu_ptr() and comments are > added for why it is used. >
Andrew & Michal,
Here's a fix that's a follow on patch instead of an updated patch as Michal has suggested. I've updated the comments a bit to make it clearer.
Thanks.
Tim
--->8--- Date: Tue, 17 Jan 2017 12:57:00 -0800 Subject: [PATCH] mm/swap: Use raw_cpu_ptr over this_cpu_ptr for swap slots access To: Andrew Morton <akpm@linux-foundation.org> Cc: Ying Huang <ying.huang@intel.com>, 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>, Michal Hocko <mhocko@kernel.org>, Hillf Danton <hillf.zj@alibaba-inc.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Jonathan Corbet <corbet@lwn.net>
From: "Huang, Ying" <ying.huang@intel.com>
The usage of this_cpu_ptr in get_swap_page causes a bug warning as it is used in pre-emptible code.
[ 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
Logic wise, We do allow pre-emption as per cpu ptr cache->slots is protected by the mutex cache->alloc_lock. We switch the inappropriately used this_cpu_ptr to raw_cpu_ptr for per cpu ptr access of cache->slots.
Reported-by: Michal Hocko <mhocko@kernel.org> Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> --- mm/swap_slots.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/swap_slots.c b/mm/swap_slots.c index 8cf941e..9b5bc86 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -303,7 +303,16 @@ swp_entry_t get_swap_page(void) swp_entry_t entry, *pentry; struct swap_slots_cache *cache; - cache = this_cpu_ptr(&swp_slots); + /* + * Preemption is allowed here, because we may sleep + * in refill_swap_slots_cache(). But it is safe, because + * accesses to the per-CPU data structure are protected by the + * mutex cache->alloc_lock. + * + * The alloc path here does not touch cache->slots_ret + * so cache->free_lock is not taken. + */ + cache = raw_cpu_ptr(&swp_slots); entry.val = 0; if (check_cache_active()) { -- 2.5.5 [unhandled content-type:application/pgp-signature] | |