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rcu: Convert grace-period requests to ->gp_seq

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This commit converts the grace-period request code paths from ->completed
and ->gpnum to ->gp_seq.  The need_future_gp_element() macro encapsulates
the shift operation required to use ->gp_seq as an index to the
->need_future_gp[] array.  The rcu_cbs_completed() function is removed
in favor of the rcu_seq_snap() function.  The rcu_start_this_gp()
gets some temporary consistency checks and uses rcu_seq_done(),
rcu_seq_current(), rcu_seq_state(), and rcu_gp_in_progress() in place
of the earlier open-coded comparisons of ->gpnum and ->completed.
The rcu_future_gp_cleanup() function replaces use of ->completed
with ->gp_seq.  The rcu_accelerate_cbs() function replaces a call to
rcu_cbs_completed() with one to rcu_seq_snap().  The rcu_advance_cbs()
function replaces an access to >completed with one to ->gp_seq and adds
some temporary warnings.  The rcu_nocb_wait_gp() function replaces a
call to rcu_cbs_completed() with one to rcu_seq_snap() and an open-coded
comparison with rcu_seq_done().

The temporary warnings will be removed when the various ->gpnum and
->completed fields are removed.  Their purpose is to locate code who
might still be using ->gpnum and ->completed.  (Much easier that way
than trying to trace down the causes of too-short grace periods and
grace-period hangs!)

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2018-04-30 10:57:36 -07:00
parent d43a5d32e1
commit 29365e563b
3 changed files with 24 additions and 68 deletions
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6
kernel/rcu/tree_plugin.h
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@@ -2105,7 +2105,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
struct rcu_node *rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
c = rcu_cbs_completed(rdp->rsp, rnp);
c = rcu_seq_snap(&rdp->rsp->gp_seq);
needwake = rcu_start_this_gp(rnp, rdp, c);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (needwake)
@@ -2118,8 +2118,8 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait"));
for (;;) {
swait_event_interruptible(
rnp->nocb_gp_wq[c & 0x1],
(d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
rnp->nocb_gp_wq[rcu_seq_ctr(c) & 0x1],
(d = rcu_seq_done(&rnp->gp_seq, c)));
if (likely(d))
break;
WARN_ON(signal_pending(current));