xarray: add the xa_lock to the radix_tree_root

This results in no change in structure size on 64-bit machines as it
fits in the padding between the gfp_t and the void *.  32-bit machines
will grow the structure from 8 to 12 bytes.  Almost all radix trees are
protected with (at least) a spinlock, so as they are converted from
radix trees to xarrays, the data structures will shrink again.

Initialising the spinlock requires a name for the benefit of lockdep, so
RADIX_TREE_INIT() now needs to know the name of the radix tree it's
initialising, and so do IDR_INIT() and IDA_INIT().

Also add the xa_lock() and xa_unlock() family of wrappers to make it
easier to use the lock.  If we could rely on -fplan9-extensions in the
compiler, we could avoid all of this syntactic sugar, but that wasn't
added until gcc 4.6.

Link: http://lkml.kernel.org/r/20180313132639.17387-8-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/f2fs/gc.c

@@ -1015,7 +1015,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 	unsigned int init_segno = segno;
 	struct gc_inode_list gc_list = {
 		.ilist = LIST_HEAD_INIT(gc_list.ilist),
-		.iroot = RADIX_TREE_INIT(GFP_NOFS),
+		.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
 	};
 
 	trace_f2fs_gc_begin(sbi->sb, sync, background,

include/linux/idr.h

@@ -32,27 +32,28 @@ struct idr {
 #define IDR_RT_MARKER	(ROOT_IS_IDR | (__force gfp_t)			\
 					(1 << (ROOT_TAG_SHIFT + IDR_FREE)))
 
-#define IDR_INIT_BASE(base) {						\
-	.idr_rt = RADIX_TREE_INIT(IDR_RT_MARKER),			\
+#define IDR_INIT_BASE(name, base) {					\
+	.idr_rt = RADIX_TREE_INIT(name, IDR_RT_MARKER),			\
 	.idr_base = (base),						\
 	.idr_next = 0,							\
 }
 
 /**
  * IDR_INIT() - Initialise an IDR.
+ * @name: Name of IDR.
  *
  * A freshly-initialised IDR contains no IDs.
  */
-#define IDR_INIT	IDR_INIT_BASE(0)
+#define IDR_INIT(name)	IDR_INIT_BASE(name, 0)
 
 /**
- * DEFINE_IDR() - Define a statically-allocated IDR
- * @name: Name of IDR
+ * DEFINE_IDR() - Define a statically-allocated IDR.
+ * @name: Name of IDR.
  *
  * An IDR defined using this macro is ready for use with no additional
  * initialisation required.  It contains no IDs.
  */
-#define DEFINE_IDR(name)	struct idr name = IDR_INIT
+#define DEFINE_IDR(name)	struct idr name = IDR_INIT(name)
 
 /**
  * idr_get_cursor - Return the current position of the cyclic allocator
@@ -219,10 +220,10 @@ struct ida {
 	struct radix_tree_root	ida_rt;
 };
 
-#define IDA_INIT	{						\
-	.ida_rt = RADIX_TREE_INIT(IDR_RT_MARKER | GFP_NOWAIT),		\
+#define IDA_INIT(name)	{						\
+	.ida_rt = RADIX_TREE_INIT(name, IDR_RT_MARKER | GFP_NOWAIT),	\
 }
-#define DEFINE_IDA(name)	struct ida name = IDA_INIT
+#define DEFINE_IDA(name)	struct ida name = IDA_INIT(name)
 
 int ida_pre_get(struct ida *ida, gfp_t gfp_mask);
 int ida_get_new_above(struct ida *ida, int starting_id, int *p_id);

include/linux/radix-tree.h

@@ -110,20 +110,23 @@ struct radix_tree_node {
 #define ROOT_TAG_SHIFT	(__GFP_BITS_SHIFT)
 
 struct radix_tree_root {
+	spinlock_t		xa_lock;
 	gfp_t			gfp_mask;
 	struct radix_tree_node	__rcu *rnode;
 };
 
-#define RADIX_TREE_INIT(mask)	{					\
+#define RADIX_TREE_INIT(name, mask)	{				\
+	.xa_lock = __SPIN_LOCK_UNLOCKED(name.xa_lock),			\
 	.gfp_mask = (mask),						\
 	.rnode = NULL,							\
 }
 
 #define RADIX_TREE(name, mask) \
-	struct radix_tree_root name = RADIX_TREE_INIT(mask)
+	struct radix_tree_root name = RADIX_TREE_INIT(name, mask)
 
 #define INIT_RADIX_TREE(root, mask)					\
 do {									\
+	spin_lock_init(&(root)->xa_lock);				\
 	(root)->gfp_mask = (mask);					\
 	(root)->rnode = NULL;						\
 } while (0)

include/linux/xarray.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+#ifndef _LINUX_XARRAY_H
+#define _LINUX_XARRAY_H
+/*
+ * eXtensible Arrays
+ * Copyright (c) 2017 Microsoft Corporation
+ * Author: Matthew Wilcox <mawilcox@microsoft.com>
+ */
+
+#include <linux/spinlock.h>
+
+#define xa_trylock(xa)		spin_trylock(&(xa)->xa_lock)
+#define xa_lock(xa)		spin_lock(&(xa)->xa_lock)
+#define xa_unlock(xa)		spin_unlock(&(xa)->xa_lock)
+#define xa_lock_bh(xa)		spin_lock_bh(&(xa)->xa_lock)
+#define xa_unlock_bh(xa)	spin_unlock_bh(&(xa)->xa_lock)
+#define xa_lock_irq(xa)		spin_lock_irq(&(xa)->xa_lock)
+#define xa_unlock_irq(xa)	spin_unlock_irq(&(xa)->xa_lock)
+#define xa_lock_irqsave(xa, flags) \
+				spin_lock_irqsave(&(xa)->xa_lock, flags)
+#define xa_unlock_irqrestore(xa, flags) \
+				spin_unlock_irqrestore(&(xa)->xa_lock, flags)
+
+#endif /* _LINUX_XARRAY_H */

kernel/pid.c

@@ -70,7 +70,7 @@ int pid_max_max = PID_MAX_LIMIT;
  */
 struct pid_namespace init_pid_ns = {
 	.kref = KREF_INIT(2),
-	.idr = IDR_INIT,
+	.idr = IDR_INIT(init_pid_ns.idr),
 	.pid_allocated = PIDNS_ADDING,
 	.level = 0,
 	.child_reaper = &init_task,

tools/include/linux/spinlock.h

@@ -7,6 +7,7 @@
 
 #define spinlock_t		pthread_mutex_t
 #define DEFINE_SPINLOCK(x)	pthread_mutex_t x = PTHREAD_MUTEX_INITIALIZER;
+#define __SPIN_LOCK_UNLOCKED(x)	(pthread_mutex_t)PTHREAD_MUTEX_INITIALIZER
 
 #define spin_lock_irqsave(x, f)		(void)f, pthread_mutex_lock(x)
 #define spin_unlock_irqrestore(x, f)	(void)f, pthread_mutex_unlock(x)