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| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2017-07-10 15:49:29 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-07-10 16:32:32 -0700 |
| commit | f07e0f849a921ec8c0b509c8b8030455a2b21f7f (patch) | |
| tree | 5b3a6a4174700b917bdfe5f31eac21ec4f9f9909 | |
| parent | b002529d256307602c669d1886c0b953b52b8700 (diff) | |
| download | talos-obmc-linux-f07e0f849a921ec8c0b509c8b8030455a2b21f7f.tar.gz talos-obmc-linux-f07e0f849a921ec8c0b509c8b8030455a2b21f7f.zip | |
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>
| -rw-r--r-- | mm/swap_slots.c | 5 |
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; } |
