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Date: Tue, 10 Nov 2009 03:19:12 GMT From: "tip-bot for Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-tip-commits@...r.kernel.org Cc: linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com, hpa@...or.com, mingo@...hat.com, tglx@...utronix.de, mingo@...e.hu Subject: [tip:core/rcu] rcu: Fix note_new_gpnum() uses of ->gpnum Commit-ID: 9160306e6f5b68bb64630c9031c517ca1cf463db Gitweb: http://git.kernel.org/tip/9160306e6f5b68bb64630c9031c517ca1cf463db Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> AuthorDate: Mon, 2 Nov 2009 13:52:29 -0800 Committer: Ingo Molnar <mingo@...e.hu> CommitDate: Tue, 10 Nov 2009 04:12:11 +0100 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@...ux.vnet.ibm.com> Cc: laijs@...fujitsu.com Cc: dipankar@...ibm.com Cc: mathieu.desnoyers@...ymtl.ca Cc: josh@...htriplett.org Cc: dvhltc@...ibm.com Cc: niv@...ibm.com Cc: peterz@...radead.org Cc: rostedt@...dmis.org Cc: Valdis.Kletnieks@...edu Cc: dhowells@...hat.com Cc: <stable@...nel.org> # .32.x LKML-Reference: <12571987492350-git-send-email-> Signed-off-by: Ingo Molnar <mingo@...e.hu> --- kernel/rcutree.c | 32 +++++++++++++++++++++++++++----- 1 files changed, 27 insertions(+), 5 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 9e068d1..ec007dd 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) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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