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rcu: Make non-preemptive schedule be Tasks RCU quiescent state

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Currently, a call to schedule() acts as a Tasks RCU quiescent state
only if a context switch actually takes place.  However, just the
call to schedule() guarantees that the calling task has moved off of
whatever tracing trampoline that it might have been one previously.
This commit therefore plumbs schedule()'s "preempt" parameter into
rcu_note_context_switch(), which then records the Tasks RCU quiescent
state, but only if this call to schedule() was -not- due to a preemption.

To avoid adding overhead to the common-case context-switch path,
this commit hides the rcu_note_context_switch() check under an existing
non-common-case check.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-04-11 15:50:41 -07:00
parent 0497b489b8
commit bcbfdd01dc
6 changed files with 43 additions and 11 deletions
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11
include/linux/rcupdate.h
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@ -363,15 +363,20 @@ static inline void rcu_init_nohz(void)
#ifdef CONFIG_TASKS_RCU
#define TASKS_RCU(x) x
extern struct srcu_struct tasks_rcu_exit_srcu;
#define rcu_note_voluntary_context_switch(t) \
#define rcu_note_voluntary_context_switch_lite(t) \
do { \
rcu_all_qs(); \
if (READ_ONCE((t)->rcu_tasks_holdout)) \
WRITE_ONCE((t)->rcu_tasks_holdout, false); \
} while (0)
#define rcu_note_voluntary_context_switch(t) \
do { \
rcu_all_qs(); \
rcu_note_voluntary_context_switch_lite(t); \
} while (0)
#else /* #ifdef CONFIG_TASKS_RCU */
#define TASKS_RCU(x) do { } while (0)
#define rcu_note_voluntary_context_switch(t) rcu_all_qs()
#define rcu_note_voluntary_context_switch_lite(t) do { } while (0)
#define rcu_note_voluntary_context_switch(t) rcu_all_qs()
#endif /* #else #ifdef CONFIG_TASKS_RCU */
/**