diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2009-11-02 13:52:29 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-11-10 04:12:11 +0100 |
| commit | 9160306e6f5b68bb64630c9031c517ca1cf463db (patch) | |
| tree | d8f78f99d417f34121c21e45a4675b2b1d5c2674 /kernel/rcutree.c | |
| parent | d09b62dfa336447c52a5ec9bb88adbc479b0f3b8 (diff) | |
rcu: Fix note_new_gpnum() uses of ->gpnum
Impose a clear locking design on the note_new_gpnum()
function's use of the ->gpnum counter. This is done by updating
rdp->gpnum only from the corresponding leaf rcu_node structure's
rnp->gpnum field, and even then only under the protection of
that same rcu_node structure's ->lock field. Performance and
scalability are maintained using a form of double-checked
locking, and excessive spinning is avoided by use of the
spin_trylock() function. The use of spin_trylock() is safe due
to the fact that CPUs who fail to acquire this lock will try
again later. The hierarchical nature of the rcu_node data
structure limits contention (which could be limited further if
need be using the RCU_FANOUT kernel parameter).
Without this patch, obscure but quite possible races could
result in a quiescent state that occurred during one grace
period to be accounted to the following grace period, causing
this following grace period to end prematurely. Not good!
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
Cc: <stable@kernel.org> # .32.x
LKML-Reference: <12571987492350-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/rcutree.c')
| -rw-r--r-- | kernel/rcutree.c | 32 |
1 files changed, 27 insertions, 5 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 9e068d112153..ec007dd22632 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -540,13 +540,33 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) /* * Update CPU-local rcu_data state to record the newly noticed grace period. * This is used both when we started the grace period and when we notice - * that someone else started the grace period. + * that someone else started the grace period. The caller must hold the + * ->lock of the leaf rcu_node structure corresponding to the current CPU, + * and must have irqs disabled. */ +static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) +{ + if (rdp->gpnum != rnp->gpnum) { + rdp->qs_pending = 1; + rdp->passed_quiesc = 0; + rdp->gpnum = rnp->gpnum; + } +} + static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp) { - rdp->qs_pending = 1; - rdp->passed_quiesc = 0; - rdp->gpnum = rsp->gpnum; + unsigned long flags; + struct rcu_node *rnp; + + local_irq_save(flags); + rnp = rdp->mynode; + if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */ + !spin_trylock(&rnp->lock)) { /* irqs already off, retry later. */ + local_irq_restore(flags); + return; + } + __note_new_gpnum(rsp, rnp, rdp); + spin_unlock_irqrestore(&rnp->lock, flags); } /* @@ -637,6 +657,9 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat */ rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; + + /* Set state so that this CPU will detect the next quiescent state. */ + __note_new_gpnum(rsp, rnp, rdp); } /* @@ -664,7 +687,6 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); dyntick_record_completed(rsp, rsp->completed - 1); - note_new_gpnum(rsp, rdp); /* Special-case the common single-level case. */ if (NUM_RCU_NODES == 1) { |