RCU Archive on lore.kernel.org
 help / color / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Josh Triplett <josh@joshtriplett.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	rcu@vger.kernel.org
Subject: Re: [PATCH 3/8] srcu: Use local_lock() for per-CPU struct srcu_data access
Date: Wed, 20 May 2020 15:27:55 +0200
Message-ID: <20200520132755.GM317569@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200520120608.mwros5jurmidxxfv@linutronix.de>

On Wed, May 20, 2020 at 02:06:08PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-05-20 12:24:07 [+0200], Peter Zijlstra wrote:

> > Would it perhaps make sense to stick the local_lock in struct srcu_data ?
> 
> In that case we would need something for pointer stability before the
> lock is acquired.

Maybe I need sleep; but I think this will work.

 &x->foo = x + foo-offset

 this_cpu_ptr(x) = x + cpu-offset

 &this_cpu_ptr(x)->foo = (x + cpu-offset) + foo-offset
                       = (x + foo-offset) + cpu-offset
		       = this_cpu_ptr(&x->foo)

---
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -13,6 +13,7 @@
 
 #include <linux/rcu_node_tree.h>
 #include <linux/completion.h>
+#include <linux/locallock.h>
 
 struct srcu_node;
 struct srcu_struct;
@@ -22,6 +23,8 @@ struct srcu_struct;
  * to rcu_node.
  */
 struct srcu_data {
+	struct local_lock llock;
+
 	/* Read-side state. */
 	unsigned long srcu_lock_count[2];	/* Locks per CPU. */
 	unsigned long srcu_unlock_count[2];	/* Unlocks per CPU. */
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -778,13 +778,13 @@ static bool srcu_might_be_idle(struct sr
 	unsigned long tlast;
 
 	/* If the local srcu_data structure has callbacks, not idle.  */
-	local_irq_save(flags);
+	local_lock_irqsave(&ssp->sda->llock, flags);
 	sdp = this_cpu_ptr(ssp->sda);
 	if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
-		local_irq_restore(flags);
+		local_unlock_irqrestore(&ssp->sda->llock, flags);
 		return false; /* Callbacks already present, so not idle. */
 	}
-	local_irq_restore(flags);
+	local_unlock_irqrestore(&ssp->sda->llock, flags);
 
 	/*
 	 * No local callbacks, so probabalistically probe global state.
@@ -864,7 +864,7 @@ static void __call_srcu(struct srcu_stru
 	}
 	rhp->func = func;
 	idx = srcu_read_lock(ssp);
-	local_irq_save(flags);
+	local_lock_irqsave(&ssp->sda->llock, flags);
 	sdp = this_cpu_ptr(ssp->sda);
 	spin_lock_rcu_node(sdp);
 	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
@@ -880,7 +880,8 @@ static void __call_srcu(struct srcu_stru
 		sdp->srcu_gp_seq_needed_exp = s;
 		needexp = true;
 	}
-	spin_unlock_irqrestore_rcu_node(sdp, flags);
+	spin_unlock_rcu_node(sdp);
+	local_unlock_irqrestore(&ssp->sda->llock, flags);
 	if (needgp)
 		srcu_funnel_gp_start(ssp, sdp, s, do_norm);
 	else if (needexp)

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200519201912.1564477-1-bigeasy@linutronix.de>
2020-05-19 20:19 ` Sebastian Andrzej Siewior
2020-05-20 10:24   ` Peter Zijlstra
2020-05-20 12:06     ` Sebastian Andrzej Siewior
2020-05-20 13:27       ` Peter Zijlstra [this message]
2020-05-20 17:42       ` Joel Fernandes
2020-05-20 18:28         ` Sebastian Andrzej Siewior
2020-05-20 18:35           ` Peter Zijlstra
2020-05-20 18:44             ` Joel Fernandes
2020-05-20 18:50               ` Uladzislau Rezki
2020-05-20 18:59           ` Joel Fernandes
2020-05-20 18:43       ` Paul E. McKenney
2020-05-22 15:12         ` Sebastian Andrzej Siewior
2020-05-22 17:39           ` Paul E. McKenney
2020-05-23 15:08             ` Sebastian Andrzej Siewior
2020-05-23 16:59               ` Paul E. McKenney
2020-05-24 19:03               ` Sebastian Andrzej Siewior
2020-05-25  3:27                 ` Paul E. McKenney
2020-05-26 13:41                   ` [PATCH] srcu: Avoid local_irq_save() before acquiring spinlock_t Sebastian Andrzej Siewior
2020-05-26 16:16                     ` Paul E. McKenney
2020-05-26 16:31                       ` Sebastian Andrzej Siewior

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200520132755.GM317569@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=bigeasy@linutronix.de \
    --cc=jiangshanlai@gmail.com \
    --cc=josh@joshtriplett.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mathieu.desnoyers@efficios.com \
    --cc=mingo@kernel.org \
    --cc=paulmck@kernel.org \
    --cc=rcu@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

RCU Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/rcu/0 rcu/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 rcu rcu/ https://lore.kernel.org/rcu \
		rcu@vger.kernel.org
	public-inbox-index rcu

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.rcu


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git