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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-06-25 15:00:58 -0700 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-17 14:58:51 -0700 |
commit | 28f00767e3db933cacc3030f4d9736acd037be2c (patch) | |
tree | cd49629a604b727bc8d871870e3bb27000907210 /kernel/rcu/tree.c | |
parent | 3a6d7c64d78a78d279851524d39999637a549363 (diff) | |
download | op-kernel-dev-28f00767e3db933cacc3030f4d9736acd037be2c.zip op-kernel-dev-28f00767e3db933cacc3030f4d9736acd037be2c.tar.gz |
rcu: Abstract sequence counting from synchronize_sched_expedited()
This commit creates rcu_exp_gp_seq_start() and rcu_exp_gp_seq_end() to
bracket an expedited grace period, rcu_exp_gp_seq_snap() to snapshot the
sequence counter, and rcu_exp_gp_seq_done() to check to see if a full
expedited grace period has elapsed since the snapshot. These will be
applied to synchronize_rcu_expedited(). These are defined in terms of
underlying rcu_seq_start(), rcu_seq_end(), rcu_seq_snap(), rcu_seq_done(),
which will be applied to _rcu_barrier().
One reason that this commit doesn't use the seqcount primitives themselves
is that the smp_wmb() in those primitive is insufficient due to the fact
that expedited grace periods do reads as well as writes. In addition,
the read-side seqcount primitives detect a potentially partial change,
where the expedited primitives instead need a guaranteed full change.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/tree.c')
-rw-r--r-- | kernel/rcu/tree.c | 68 |
1 files changed, 58 insertions, 10 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c5c8509..67fe757 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3255,6 +3255,60 @@ void cond_synchronize_rcu(unsigned long oldstate) } EXPORT_SYMBOL_GPL(cond_synchronize_rcu); +/* Adjust sequence number for start of update-side operation. */ +static void rcu_seq_start(unsigned long *sp) +{ + WRITE_ONCE(*sp, *sp + 1); + smp_mb(); /* Ensure update-side operation after counter increment. */ + WARN_ON_ONCE(!(*sp & 0x1)); +} + +/* Adjust sequence number for end of update-side operation. */ +static void rcu_seq_end(unsigned long *sp) +{ + smp_mb(); /* Ensure update-side operation before counter increment. */ + WRITE_ONCE(*sp, *sp + 1); + WARN_ON_ONCE(*sp & 0x1); +} + +/* Take a snapshot of the update side's sequence number. */ +static unsigned long rcu_seq_snap(unsigned long *sp) +{ + unsigned long s; + + smp_mb(); /* Caller's modifications seen first by other CPUs. */ + s = (READ_ONCE(*sp) + 3) & ~0x1; + smp_mb(); /* Above access must not bleed into critical section. */ + return s; +} + +/* + * Given a snapshot from rcu_seq_snap(), determine whether or not a + * full update-side operation has occurred. + */ +static bool rcu_seq_done(unsigned long *sp, unsigned long s) +{ + return ULONG_CMP_GE(READ_ONCE(*sp), s); +} + +/* Wrapper functions for expedited grace periods. */ +static void rcu_exp_gp_seq_start(struct rcu_state *rsp) +{ + rcu_seq_start(&rsp->expedited_sequence); +} +static void rcu_exp_gp_seq_end(struct rcu_state *rsp) +{ + rcu_seq_end(&rsp->expedited_sequence); +} +static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp) +{ + return rcu_seq_snap(&rsp->expedited_sequence); +} +static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s) +{ + return rcu_seq_done(&rsp->expedited_sequence, s); +} + static int synchronize_sched_expedited_cpu_stop(void *data) { struct rcu_state *rsp = data; @@ -3269,7 +3323,7 @@ static int synchronize_sched_expedited_cpu_stop(void *data) static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp, atomic_long_t *stat, unsigned long s) { - if (ULONG_CMP_GE(READ_ONCE(rsp->expedited_sequence), s)) { + if (rcu_exp_gp_seq_done(rsp, s)) { if (rnp) mutex_unlock(&rnp->exp_funnel_mutex); /* Ensure test happens before caller kfree(). */ @@ -3306,9 +3360,7 @@ void synchronize_sched_expedited(void) struct rcu_state *rsp = &rcu_sched_state; /* Take a snapshot of the sequence number. */ - smp_mb(); /* Caller's modifications seen first by other CPUs. */ - s = (READ_ONCE(rsp->expedited_sequence) + 3) & ~0x1; - smp_mb(); /* Above access must not bleed into critical section. */ + s = rcu_exp_gp_seq_snap(rsp); if (!try_get_online_cpus()) { /* CPU hotplug operation in flight, fall back to normal GP. */ @@ -3339,9 +3391,7 @@ void synchronize_sched_expedited(void) if (sync_sched_exp_wd(rsp, rnp0, &rsp->expedited_workdone2, s)) return; - WRITE_ONCE(rsp->expedited_sequence, rsp->expedited_sequence + 1); - smp_mb(); /* Ensure expedited GP seen after counter increment. */ - WARN_ON_ONCE(!(rsp->expedited_sequence & 0x1)); + rcu_exp_gp_seq_start(rsp); /* Stop each CPU that is online, non-idle, and not us. */ init_waitqueue_head(&rsp->expedited_wq); @@ -3364,9 +3414,7 @@ void synchronize_sched_expedited(void) wait_event(rsp->expedited_wq, !atomic_read(&rsp->expedited_need_qs)); - smp_mb(); /* Ensure expedited GP seen before counter increment. */ - WRITE_ONCE(rsp->expedited_sequence, rsp->expedited_sequence + 1); - WARN_ON_ONCE(rsp->expedited_sequence & 0x1); + rcu_exp_gp_seq_end(rsp); mutex_unlock(&rnp0->exp_funnel_mutex); smp_mb(); /* ensure subsequent action seen after grace period. */ |