From: Mike Galbraith <umgwanakikbuti@gmail.com>
Date: Thu, 31 Mar 2016 04:08:28 +0200
Subject: drivers/block/zram: Replace bit spinlocks with rtmutex for -rt
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: fec3d3077c5c5fd05b721555b9f66b1eca48433c
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

They're nondeterministic, and lead to ___might_sleep() splats in -rt.
OTOH, they're a lot less wasteful than an rtmutex per page.

Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 drivers/block/zram/zram_drv.c |   12 ++++++++++++
 drivers/block/zram/zram_drv.h |   19 +++++++++++++++++++
 2 files changed, 31 insertions(+)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -759,12 +759,22 @@ static DEVICE_ATTR_RO(debug_stat);
 
 static void zram_slot_lock(struct zram *zram, u32 index)
 {
+#ifndef CONFIG_PREEMPT_RT_BASE
 	bit_spin_lock(ZRAM_ACCESS, &zram->table[index].value);
+#else
+	spin_lock(&zram->table[index].lock);
+	__set_bit(ZRAM_ACCESS, &zram->table[index].value);
+#endif
 }
 
 static void zram_slot_unlock(struct zram *zram, u32 index)
 {
+#ifndef CONFIG_PREEMPT_RT_BASE
 	bit_spin_unlock(ZRAM_ACCESS, &zram->table[index].value);
+#else
+	spin_unlock(&zram->table[index].lock);
+	__clear_bit(ZRAM_ACCESS, &zram->table[index].value);
+#endif
 }
 
 static void zram_meta_free(struct zram *zram, u64 disksize)
@@ -795,6 +805,8 @@ static bool zram_meta_alloc(struct zram
 		return false;
 	}
 
+	zram_meta_init_table_locks(zram, disksize);
+
 	return true;
 }
 
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -76,6 +76,9 @@ struct zram_table_entry {
 		unsigned long element;
 	};
 	unsigned long value;
+#ifdef CONFIG_PREEMPT_RT_BASE
+	spinlock_t lock;
+#endif
 };
 
 struct zram_stats {
@@ -124,4 +127,20 @@ struct zram {
 	spinlock_t bitmap_lock;
 #endif
 };
+
+#ifndef CONFIG_PREEMPT_RT_BASE
+static inline void zram_meta_init_table_locks(struct zram *zram, u64 disksize) { }
+#else /* CONFIG_PREEMPT_RT_BASE */
+static inline void zram_meta_init_table_locks(struct zram *zram, u64 disksize)
+{
+        size_t num_pages = disksize >> PAGE_SHIFT;
+        size_t index;
+
+        for (index = 0; index < num_pages; index++) {
+		spinlock_t *lock = &zram->table[index].lock;
+		spin_lock_init(lock);
+        }
+}
+#endif /* CONFIG_PREEMPT_RT_BASE */
+
 #endif