From 07079d5357a4d53c2b13126c4a38fb40e6e04966 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 4 Jan 2010 15:09:02 -0800 Subject: [PATCH] rcu: Prohibit starting new grace periods while forcing quiescent states Reduce the number and variety of race conditions by prohibiting the start of a new grace period while force_quiescent_state() is active. A new fqs_active flag in the rcu_state structure is used to trace whether or not force_quiescent_state() is active, and this new flag is tested by rcu_start_gp(). If the CPU that closed out the last grace period needs another grace period, this new grace period may be delayed up to one scheduling-clock tick, but it will eventually get started. Signed-off-by: Paul E. McKenney 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: <126264655052-git-send-email-> Signed-off-by: Ingo Molnar --- kernel/rcutree.c | 31 +++++++++++++++++-------------- kernel/rcutree.h | 2 ++ 2 files changed, 19 insertions(+), 14 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d42ad30c4d70..41688ff60e07 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -659,7 +659,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) struct rcu_data *rdp = rsp->rda[smp_processor_id()]; struct rcu_node *rnp = rcu_get_root(rsp); - if (!cpu_needs_another_gp(rsp, rdp)) { + if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) { if (rnp->completed == rsp->completed) { spin_unlock_irqrestore(&rnp->lock, flags); return; @@ -1195,6 +1195,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) struct rcu_node *rnp = rcu_get_root(rsp); u8 signaled; u8 forcenow; + u8 gpdone; if (!rcu_gp_in_progress(rsp)) return; /* No grace period in progress, nothing to force. */ @@ -1206,15 +1207,16 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) (long)(rsp->jiffies_force_qs - jiffies) >= 0) goto unlock_fqs_ret; /* no emergency and done recently. */ rsp->n_force_qs++; - spin_lock(&rnp->lock); + spin_lock(&rnp->lock); /* irqs already disabled */ lastcomp = rsp->gpnum - 1; signaled = rsp->signaled; rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; if(!rcu_gp_in_progress(rsp)) { rsp->n_force_qs_ngp++; - spin_unlock(&rnp->lock); + spin_unlock(&rnp->lock); /* irqs remain disabled */ goto unlock_fqs_ret; /* no GP in progress, time updated. */ } + rsp->fqs_active = 1; switch (signaled) { case RCU_GP_IDLE: case RCU_GP_INIT: @@ -1223,15 +1225,16 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) case RCU_SAVE_DYNTICK: - spin_unlock(&rnp->lock); + spin_unlock(&rnp->lock); /* irqs remain disabled */ if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK) break; /* So gcc recognizes the dead code. */ /* Record dyntick-idle state. */ - if (rcu_process_dyntick(rsp, lastcomp, - dyntick_save_progress_counter)) - goto unlock_fqs_ret; - spin_lock(&rnp->lock); + gpdone = rcu_process_dyntick(rsp, lastcomp, + dyntick_save_progress_counter); + spin_lock(&rnp->lock); /* irqs already disabled */ + if (gpdone) + break; /* fall into next case. */ case RCU_SAVE_COMPLETED: @@ -1252,17 +1255,17 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) case RCU_FORCE_QS: /* Check dyntick-idle state, send IPI to laggarts. */ - spin_unlock(&rnp->lock); - if (rcu_process_dyntick(rsp, rsp->completed_fqs, - rcu_implicit_dynticks_qs)) - goto unlock_fqs_ret; + spin_unlock(&rnp->lock); /* irqs remain disabled */ + gpdone = rcu_process_dyntick(rsp, rsp->completed_fqs, + rcu_implicit_dynticks_qs); /* Leave state in case more forcing is required. */ - spin_lock(&rnp->lock); + spin_lock(&rnp->lock); /* irqs already disabled */ break; } - spin_unlock(&rnp->lock); + rsp->fqs_active = 0; + spin_unlock(&rnp->lock); /* irqs remain disabled */ unlock_fqs_ret: spin_unlock_irqrestore(&rsp->fqslock, flags); } diff --git a/kernel/rcutree.h b/kernel/rcutree.h index d2a0046f63b2..dc386a7c634f 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -277,6 +277,8 @@ struct rcu_state { u8 signaled ____cacheline_internodealigned_in_smp; /* Force QS state. */ + u8 fqs_active; /* force_quiescent_state() */ + /* is running. */ long gpnum; /* Current gp number. */ long completed; /* # of last completed gp. */