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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2017-07-10 15:49:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-10 16:32:32 -0700
commitf07e0f849a921ec8c0b509c8b8030455a2b21f7f (patch)
tree5b3a6a4174700b917bdfe5f31eac21ec4f9f9909 /mm/swap_slots.c
parentb002529d256307602c669d1886c0b953b52b8700 (diff)
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mm/swap_slots.c: don't disable preemption while taking the per-CPU cache
get_cpu_var() disables preemption and returns the per-CPU version of the variable. Disabling preemption is useful to ensure atomic access to the variable within the critical section. In this case however, after the per-CPU version of the variable is obtained the ->free_lock is acquired. For that reason it seems the raw accessor could be used. It only seems that ->slots_ret should be retested (because with disabled preemption this variable can not be set to NULL otherwise). This popped up during PREEMPT-RT testing because it tries to take spinlocks in a preempt disabled section. In RT, spinlocks can sleep. Link: http://lkml.kernel.org/r/20170623114755.2ebxdysacvgxzott@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ying Huang <ying.huang@intel.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.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 90c1032a8ac3..13a174006b91 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -273,11 +273,11 @@ int free_swap_slot(swp_entry_t entry)
{
struct swap_slots_cache *cache;
- cache = &get_cpu_var(swp_slots);
+ cache = raw_cpu_ptr(&swp_slots);
if (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) {
+ if (!use_swap_slot_cache || !cache->slots_ret) {
spin_unlock_irq(&cache->free_lock);
goto direct_free;
}
@@ -297,7 +297,6 @@ int free_swap_slot(swp_entry_t entry)
direct_free:
swapcache_free_entries(&entry, 1);
}
- put_cpu_var(swp_slots);
return 0;
}