Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754458AbbGQX3j (ORCPT ); Fri, 17 Jul 2015 19:29:39 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:49094 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753169AbbGQX3c (ORCPT ); Fri, 17 Jul 2015 19:29:32 -0400 X-Helo: d03dlp01.boulder.ibm.com X-MailFrom: paulmck@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 07/19] rcu: Abstract sequence counting from synchronize_sched_expedited() Date: Fri, 17 Jul 2015 16:29:12 -0700 Message-Id: <1437175764-24096-7-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1437175764-24096-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20150717232901.GA22511@linux.vnet.ibm.com> <1437175764-24096-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15071723-8236-0000-0000-00000D42E134 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5087 Lines: 136 From: "Paul E. McKenney" This commit creates rcu_exp_gp_seq_start() and rcu_exp_gp_seq_end() to bracket an expedited grace period, rcu_exp_gp_seq_snap() to snapshot the sequence counter, and rcu_exp_gp_seq_done() to check to see if a full expedited grace period has elapsed since the snapshot. These will be applied to synchronize_rcu_expedited(). These are defined in terms of underlying rcu_seq_start(), rcu_seq_end(), rcu_seq_snap(), rcu_seq_done(), which will be applied to _rcu_barrier(). One reason that this commit doesn't use the seqcount primitives themselves is that the smp_wmb() in those primitive is insufficient due to the fact that expedited grace periods do reads as well as writes. In addition, the read-side seqcount primitives detect a potentially partial change, where the expedited primitives instead need a guaranteed full change. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 58 insertions(+), 10 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c5c8509054ef..67fe75725486 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3255,6 +3255,60 @@ void cond_synchronize_rcu(unsigned long oldstate) } EXPORT_SYMBOL_GPL(cond_synchronize_rcu); +/* Adjust sequence number for start of update-side operation. */ +static void rcu_seq_start(unsigned long *sp) +{ + WRITE_ONCE(*sp, *sp + 1); + smp_mb(); /* Ensure update-side operation after counter increment. */ + WARN_ON_ONCE(!(*sp & 0x1)); +} + +/* Adjust sequence number for end of update-side operation. */ +static void rcu_seq_end(unsigned long *sp) +{ + smp_mb(); /* Ensure update-side operation before counter increment. */ + WRITE_ONCE(*sp, *sp + 1); + WARN_ON_ONCE(*sp & 0x1); +} + +/* Take a snapshot of the update side's sequence number. */ +static unsigned long rcu_seq_snap(unsigned long *sp) +{ + unsigned long s; + + smp_mb(); /* Caller's modifications seen first by other CPUs. */ + s = (READ_ONCE(*sp) + 3) & ~0x1; + smp_mb(); /* Above access must not bleed into critical section. */ + return s; +} + +/* + * Given a snapshot from rcu_seq_snap(), determine whether or not a + * full update-side operation has occurred. + */ +static bool rcu_seq_done(unsigned long *sp, unsigned long s) +{ + return ULONG_CMP_GE(READ_ONCE(*sp), s); +} + +/* Wrapper functions for expedited grace periods. */ +static void rcu_exp_gp_seq_start(struct rcu_state *rsp) +{ + rcu_seq_start(&rsp->expedited_sequence); +} +static void rcu_exp_gp_seq_end(struct rcu_state *rsp) +{ + rcu_seq_end(&rsp->expedited_sequence); +} +static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp) +{ + return rcu_seq_snap(&rsp->expedited_sequence); +} +static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s) +{ + return rcu_seq_done(&rsp->expedited_sequence, s); +} + static int synchronize_sched_expedited_cpu_stop(void *data) { struct rcu_state *rsp = data; @@ -3269,7 +3323,7 @@ static int synchronize_sched_expedited_cpu_stop(void *data) static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp, atomic_long_t *stat, unsigned long s) { - if (ULONG_CMP_GE(READ_ONCE(rsp->expedited_sequence), s)) { + if (rcu_exp_gp_seq_done(rsp, s)) { if (rnp) mutex_unlock(&rnp->exp_funnel_mutex); /* Ensure test happens before caller kfree(). */ @@ -3306,9 +3360,7 @@ void synchronize_sched_expedited(void) struct rcu_state *rsp = &rcu_sched_state; /* Take a snapshot of the sequence number. */ - smp_mb(); /* Caller's modifications seen first by other CPUs. */ - s = (READ_ONCE(rsp->expedited_sequence) + 3) & ~0x1; - smp_mb(); /* Above access must not bleed into critical section. */ + s = rcu_exp_gp_seq_snap(rsp); if (!try_get_online_cpus()) { /* CPU hotplug operation in flight, fall back to normal GP. */ @@ -3339,9 +3391,7 @@ void synchronize_sched_expedited(void) if (sync_sched_exp_wd(rsp, rnp0, &rsp->expedited_workdone2, s)) return; - WRITE_ONCE(rsp->expedited_sequence, rsp->expedited_sequence + 1); - smp_mb(); /* Ensure expedited GP seen after counter increment. */ - WARN_ON_ONCE(!(rsp->expedited_sequence & 0x1)); + rcu_exp_gp_seq_start(rsp); /* Stop each CPU that is online, non-idle, and not us. */ init_waitqueue_head(&rsp->expedited_wq); @@ -3364,9 +3414,7 @@ void synchronize_sched_expedited(void) wait_event(rsp->expedited_wq, !atomic_read(&rsp->expedited_need_qs)); - smp_mb(); /* Ensure expedited GP seen before counter increment. */ - WRITE_ONCE(rsp->expedited_sequence, rsp->expedited_sequence + 1); - WARN_ON_ONCE(rsp->expedited_sequence & 0x1); + rcu_exp_gp_seq_end(rsp); mutex_unlock(&rnp0->exp_funnel_mutex); smp_mb(); /* ensure subsequent action seen after grace period. */ -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/