The patch titled
Subject: mm/swap: Use raw_cpu_ptr over this_cpu_ptr for swap slots access
has been added to the -mm tree. Its filename is
mm-swap-add-cache-for-swap-slots-allocation-fix.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-add-cache-for-swap-slots-allocation-fix.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-swap-add-cache-for-swap-slots-allocation-fix.patch
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------------------------------------------------------
From: "Huang, Ying" <ying.huang@xxxxxxxxx>
Subject: mm/swap: Use raw_cpu_ptr over this_cpu_ptr for swap slots access
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-mmot=
m-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 ffffffff=
81a0ce06
[ 57.816019] ffffc900001939f0 ffffffff81343c2a 00000000000137a0 ffffea00=
00dfd2a0
[ 57.816019] ffff88003c49a700 ffffc90000193b10 ffffc90000193a00 ffffffff=
81343c53
[ 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.
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Reported-by: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap_slots.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff -puN mm/swap_slots.c~mm-swap-add-cache-for-swap-slots-allocation-fix mm/swap_slots.c
--- a/mm/swap_slots.c~mm-swap-add-cache-for-swap-slots-allocation-fix
+++ a/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()) {
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
mm-swap-fix-kernel-message-in-swap_info_get.patch
mm-swap-add-cluster-lock.patch
mm-swap-split-swap-cache-into-64mb-trunks.patch
mm-swap-add-cache-for-swap-slots-allocation-fix.patch
mm-swap-skip-readahead-only-when-swap-slot-cache-is-enabled.patch
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