diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2009-11-13 19:51:39 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-11-14 10:31:42 +0100 |
| commit | 2f51f9884f6a36b0fe9636d5a1937e5cbd25723b (patch) | |
| tree | 0505e111a9714b2bd022322f76e6c4de26861107 | |
| parent | 560d4bc0df9a5e63b980432282d8c2bd3559ec74 (diff) | |
rcu: Eliminate __rcu_pending() false positives
Now that there are both ->gpnum and ->completed fields in the
rcu_node structure, __rcu_pending() should check rdp->gpnum and
rdp->completed against rnp->gpnum and rdp->completed, respectively,
instead of the prior comparison against the rcu_state fields
rsp->gpnum and rsp->completed.
Given the old comparison, __rcu_pending() could return 1, resulting
in a needless raise_softirq(RCU_SOFTIRQ). This useless work would
happen if RCU responded to a scheduling-clock interrupt after the
rcu_state fields had been updated, but before the rcu_node fields
had been updated.
Changing the comparison from the rcu_state fields to the rcu_node
fields prevents this useless work from happening.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12581706991966-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | kernel/rcutree.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 24bbf2ce0605..9b36d6d7fb97 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1403,6 +1403,8 @@ EXPORT_SYMBOL_GPL(call_rcu_bh); */ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) { + struct rcu_node *rnp = rdp->mynode; + rdp->n_rcu_pending++; /* Check for CPU stalls, if enabled. */ @@ -1427,13 +1429,13 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) } /* Has another RCU grace period completed? */ - if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */ + if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */ rdp->n_rp_gp_completed++; return 1; } /* Has a new RCU grace period started? */ - if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */ + if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */ rdp->n_rp_gp_started++; return 1; } |