diff options
| author | Tim Chen | 2017-11-15 17:34:18 -0800 |
|---|---|---|
| committer | Linus Torvalds | 2017-11-15 18:21:03 -0800 |
| commit | a2e16731728a285bcfcece0feaaa8cf478d24022 (patch) | |
| tree | b4ff3a46cea6467267e250b127ca6865d00d44cc /mm/swap_slots.c | |
| parent | 3a50d14d0df5776e002a8683a290c87eeac93a21 (diff) | |
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.
[akpm@linux-foundation.org: tidy up comment]
[akpm@linux-foundation.org: fix spello in comment]
Link: http://lkml.kernel.org/r/65a9d0f133f63e66bba37b53b2fd0464b7cae771.1500677066.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Reported-by: Wenwei Tao <wenwei.tww@alibaba-inc.com>
Acked-by: Ying Huang <ying.huang@intel.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap_slots.c')
| -rw-r--r-- | mm/swap_slots.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/mm/swap_slots.c b/mm/swap_slots.c index d81cfc5a43d5..bebc19292018 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -149,6 +149,13 @@ static int alloc_swap_slot_cache(unsigned int cpu) cache->nr = 0; cache->cur = 0; cache->n_ret = 0; + /* + * We initialized 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; @@ -275,7 +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) { @@ -326,7 +333,7 @@ swp_entry_t get_swap_page(struct page *page) */ 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: |