On 03/03/13 01:11, Srivatsa S. Bhat wrote:

On 03/02/2013 06:44 PM, Lai Jiangshan wrote:

quoted

From 345a7a75c314ff567be48983e0892bc69c4452e7 Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <redacted>
Date: Sat, 2 Mar 2013 20:33:14 +0800
Subject: [PATCH] lglock: add read-preference local-global rwlock

Current lglock is not read-preference, so it can't be used on some cases
which read-preference rwlock can do. Example, get_cpu_online_atomic().

[...]

quoted

diff --git a/kernel/lglock.c b/kernel/lglock.c
index 6535a66..52e9b2c 100644
--- a/kernel/lglock.c
+++ b/kernel/lglock.c

@@ -87,3 +87,71 @@ void lg_global_unlock(struct lglock *lg)
 	preempt_enable();
 }
 EXPORT_SYMBOL(lg_global_unlock);
+
+#define FALLBACK_BASE	(1UL << 30)
+
+void lg_rwlock_local_read_lock(struct lgrwlock *lgrw)
+{
+	struct lglock *lg = &lgrw->lglock;
+
+	preempt_disable();
+	if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) {
+		rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_);
+		if (unlikely(!arch_spin_trylock(this_cpu_ptr(lg->lock)))) {
+			read_lock(&lgrw->fallback_rwlock);
+			__this_cpu_write(*lgrw->reader_refcnt, FALLBACK_BASE);
+			return;
+		}
+	}
+
+	__this_cpu_inc(*lgrw->reader_refcnt);
+}
+EXPORT_SYMBOL(lg_rwlock_local_read_lock);
+
+void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
+{
+	switch (__this_cpu_read(*lgrw->reader_refcnt)) {
+	case 1:
+		__this_cpu_write(*lgrw->reader_refcnt, 0);
+		lg_local_unlock(&lgrw->lglock);
+		return;

This should be a break, instead of a return, right?
Otherwise, there will be a preempt imbalance...

"lockdep" and "preempt" are handled in lg_local_unlock(&lgrw->lglock);

Thanks,
Lai

quoted

+	case FALLBACK_BASE:
+		__this_cpu_write(*lgrw->reader_refcnt, 0);
+		read_unlock(&lgrw->fallback_rwlock);
+		rwlock_release(&lg->lock_dep_map, 1, _RET_IP_);
+		break;
+	default:
+		__this_cpu_dec(*lgrw->reader_refcnt);
+		break;
+	}
+
+	preempt_enable();
+}

Regards,
Srivatsa S. Bhat

--
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/