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rcu-tasks: Add Kconfig option to mediate smp_mb() vs. IPI

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This commit provides a new TASKS_TRACE_RCU_READ_MB Kconfig option that
enables use of read-side memory barriers by both rcu_read_lock_trace()
and rcu_read_unlock_trace() when the are executed with the
current->trc_reader_special.b.need_mb flag set.  This flag is currently
never set.  Doing that is the subject of a later commit.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney
2020-03-18 17:16:37 -07:00
parent 238dbce39e
commit 9ae58d7bd1
3 changed files with 22 additions and 2 deletions
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3
kernel/rcu/tasks.h
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@@ -734,7 +734,8 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
{
int nq = t->trc_reader_special.b.need_qs;
if (t->trc_reader_special.b.need_mb)
if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) &&
t->trc_reader_special.b.need_mb)
smp_mb(); // Pairs with update-side barriers.
// Update .need_qs before ->trc_reader_nesting for irq/NMI handlers.
if (nq)