diff options
author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-11-02 13:33:57 -0700 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-01-16 14:59:54 -0800 |
commit | 6563de9d6f1336157c9861bcd9864e0b47d65f9d (patch) | |
tree | a7bcbcf895f02a1a5b488c6a91ac5b5a2e95033b /kernel/rcu/tree.c | |
parent | 52d7e48b86fc108e45a656d8e53e4237993c481d (diff) |
rcu: Abstract the dynticks momentary-idle operation
This commit is the first step towards full abstraction of all accesses to
the ->dynticks counter, implementing the previously open-coded atomic add
of two in a new rcu_dynticks_momentary_idle() function. This abstraction
will ease changes to the ->dynticks counter operation.
Note that this commit gets rid of the smp_mb__before_atomic() and the
smp_mb__after_atomic() calls that were previously present. The reason
that this is OK from a memory-ordering perspective is that the atomic
operation is now atomic_add_return(), which, as a value-returning atomic,
guarantees full ordering.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'kernel/rcu/tree.c')
-rw-r--r-- | kernel/rcu/tree.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index cb4e2056ccf3..14e283c351f6 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -281,6 +281,19 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ }; +/* + * Do a double-increment of the ->dynticks counter to emulate a + * momentary idle-CPU quiescent state. + */ +static void rcu_dynticks_momentary_idle(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + int special = atomic_add_return(2, &rdtp->dynticks); + + /* It is illegal to call this from idle state. */ + WARN_ON_ONCE(!(special & 0x1)); +} + DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr); EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr); @@ -300,7 +313,6 @@ EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr); static void rcu_momentary_dyntick_idle(void) { struct rcu_data *rdp; - struct rcu_dynticks *rdtp; int resched_mask; struct rcu_state *rsp; @@ -327,10 +339,7 @@ static void rcu_momentary_dyntick_idle(void) * quiescent state, with no need for this CPU to do anything * further. */ - rdtp = this_cpu_ptr(&rcu_dynticks); - smp_mb__before_atomic(); /* Earlier stuff before QS. */ - atomic_add(2, &rdtp->dynticks); /* QS. */ - smp_mb__after_atomic(); /* Later stuff after QS. */ + rcu_dynticks_momentary_idle(); break; } } |