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.deSigned-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: NMichal 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: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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