patches/srcu-replace-local_irqsave-with-a-locallock.patch

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 12 Oct 2017 18:37:12 +0200
Subject: [PATCH] srcu: replace local_irqsave() with a locallock

There are two instances which disable interrupts in order to become a
stable this_cpu_ptr() pointer. The restore part is coupled with
spin_unlock_irqrestore() which does not work on RT.
Replace the local_irq_save() call with the appropriate local_lock()
version of it.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/rcu/srcutree.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -37,6 +37,7 @@
 #include <linux/module.h>
 #include <linux/srcu.h>
 #include <linux/cpu.h>
+#include <linux/locallock.h>
 
 #include "rcu.h"
 #include "rcu_segcblist.h"
@@ -749,6 +750,8 @@ static void srcu_flip(struct srcu_struct
  * negligible when amoritized over that time period, and the extra latency
  * of a needlessly non-expedited grace period is similarly negligible.
  */
+static DEFINE_LOCAL_IRQ_LOCK(sp_llock);
+
 static bool srcu_might_be_idle(struct srcu_struct *sp)
 {
 	unsigned long curseq;
@@ -757,13 +760,13 @@ static bool srcu_might_be_idle(struct sr
 	unsigned long t;
 
 	/* If the local srcu_data structure has callbacks, not idle.  */
-	local_irq_save(flags);
+	local_lock_irqsave(sp_llock, flags);
 	sdp = this_cpu_ptr(sp->sda);
 	if (rcu_segcblist_pend_cbs(&sdp->srcu_cblist)) {
-		local_irq_restore(flags);
+		local_unlock_irqrestore(sp_llock, flags);
 		return false; /* Callbacks already present, so not idle. */
 	}
-	local_irq_restore(flags);
+	local_unlock_irqrestore(sp_llock, flags);
 
 	/*
 	 * No local callbacks, so probabalistically probe global state.
@@ -841,7 +844,7 @@ void __call_srcu(struct srcu_struct *sp,
 		return;
 	}
 	rhp->func = func;
-	local_irq_save(flags);
+	local_lock_irqsave(sp_llock, flags);
 	sdp = this_cpu_ptr(sp->sda);
 	spin_lock_rcu_node(sdp);
 	rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);
@@ -857,7 +860,8 @@ void __call_srcu(struct srcu_struct *sp,
 		sdp->srcu_gp_seq_needed_exp = s;
 		needexp = true;
 	}
-	spin_unlock_irqrestore_rcu_node(sdp, flags);
+	spin_unlock_rcu_node(sdp);
+	local_unlock_irqrestore(sp_llock, flags);
 	if (needgp)
 		srcu_funnel_gp_start(sp, sdp, s, do_norm);
 	else if (needexp)