The patch titled
Subject: mm/swap_slots.c: fix race conditions in swap_slots cache init
has been added to the -mm tree. Its filename is
mm-swap-fix-race-conditions-in-swap_slots-cache-init.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-fix-race-conditions-in-swap_slots-cache-init.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-swap-fix-race-conditions-in-swap_slots-cache-init.patch
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------------------------------------------------------
From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Subject: mm/swap_slots.c: fix race conditions in swap_slots cache init
Memory allocations can happen before the swap_slots cache initialization
is completed during cpu bring up. If we are low on memory, we could call
get_swap_page() and access swap_slots_cache before it is fully
initialized.
Add a check in get_swap_page() for initialized swap_slots_cache to prevent
this condition. Similar check already exists in free_swap_slot. Also
annotate the checks to indicate the likely condition.
We also added a memory barrier to make sure that the locks initialization
are done before the assignment of cache->slots and cache->slots_ret
pointers. This ensures the assumption that it is safe to acquire the
slots cache locks and use the slots cache when the corresponding
cache->slots or cache->slots_ret pointers are non null.
Link: http://lkml.kernel.org/r/65a9d0f133f63e66bba37b53b2fd0464b7cae771.1500677066.git.tim.c.chen@xxxxxxxxxxxxxxx
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Reported-by: Wenwei Tao <wenwei.tww@xxxxxxxxxxxxxxx>
Acked-by: Ying Huang <ying.huang@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap_slots.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff -puN mm/swap_slots.c~mm-swap-fix-race-conditions-in-swap_slots-cache-init mm/swap_slots.c
--- a/mm/swap_slots.c~mm-swap-fix-race-conditions-in-swap_slots-cache-init
+++ a/mm/swap_slots.c
@@ -148,6 +148,14 @@ static int alloc_swap_slot_cache(unsigne
cache->nr = 0;
cache->cur = 0;
cache->n_ret = 0;
+ /*
+ * We intialized alloc_lock and free_lock earlier.
+ * We use !cache->slots or !cache->slots_ret
+ * to know if it is safe to acquire the corresponding
+ * lock and use the cache. Memory barrier
+ * below ensures the assumption.
+ */
+ mb();
cache->slots = slots;
slots = NULL;
cache->slots_ret = slots_ret;
@@ -274,7 +282,7 @@ int free_swap_slot(swp_entry_t entry)
struct swap_slots_cache *cache;
cache = raw_cpu_ptr(&swp_slots);
- if (use_swap_slot_cache && cache->slots_ret) {
+ if (likely(use_swap_slot_cache && cache->slots_ret)) {
spin_lock_irq(&cache->free_lock);
/* Swap slots cache may be deactivated before acquiring lock */
if (!use_swap_slot_cache || !cache->slots_ret) {
@@ -325,7 +333,7 @@ swp_entry_t get_swap_page(struct page *p
*/
cache = raw_cpu_ptr(&swp_slots);
- if (check_cache_active()) {
+ if (likely(check_cache_active() && cache->slots)) {
mutex_lock(&cache->alloc_lock);
if (cache->slots) {
repeat:
_
Patches currently in -mm which might be from tim.c.chen@xxxxxxxxxxxxxxx are
mm-swap-fix-race-conditions-in-swap_slots-cache-init.patch
mm-swap-remove-lock_initialized-flag-from-swap_slots_cache.patch
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