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From: Dave Chinner <david@fromorbit.com>
To: linux-xfs@vger.kernel.org
Subject: [PATCH 09/27] atomic: convert to uatomic
Date: Thu, 15 Oct 2020 18:21:37 +1100
Message-ID: <20201015072155.1631135-10-david@fromorbit.com> (raw)
In-Reply-To: <20201015072155.1631135-1-david@fromorbit.com>

From: Dave Chinner <dchinner@redhat.com>

Now we have liburcu, we can make use of it's atomic variable
implementation. It is almost identical to the kernel API - it's just
got a "uatomic" prefix. liburcu also provides all the same aomtic
variable memory barriers as the kernel, so if we pull memory barrier
dependent kernel code across, it will just work with the right
barrier wrappers.

This is preparation the addition of more extensive atomic operations
the that kernel buffer cache requires to function correctly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 include/atomic.h | 60 +++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 52 insertions(+), 8 deletions(-)

diff --git a/include/atomic.h b/include/atomic.h
index 1aabecc3ae57..5860d7897ae5 100644
--- a/include/atomic.h
+++ b/include/atomic.h
@@ -7,18 +7,62 @@
 #define __ATOMIC_H__
 
 /*
- * Warning: These are not really atomic at all. They are wrappers around the
- * kernel atomic variable interface. If we do need these variables to be atomic
- * (due to multithreading of the code that uses them) we need to add some
- * pthreads magic here.
+ * Atomics are provided by liburcu.
+ *
+ * API and guidelines for which operations provide memory barriers is here:
+ *
+ * https://github.com/urcu/userspace-rcu/blob/master/doc/uatomic-api.md
+ *
+ * Unlike the kernel, the same interface supports 32 and 64 bit atomic integers.
  */
+#include <urcu/uatomic.h>
+#include "spinlock.h"
+
 typedef	int32_t	atomic_t;
 typedef	int64_t	atomic64_t;
 
-#define atomic_inc_return(x)	(++(*(x)))
-#define atomic_dec_return(x)	(--(*(x)))
+#define atomic_read(a)		uatomic_read(a)
+#define atomic_set(a, v)	uatomic_set(a, v)
+
+#define atomic_inc_return(a)	uatomic_add_return(a, 1)
+#define atomic_dec_return(a)	uatomic_sub_return(a, 1)
+
+#define atomic_inc(a)		atomic_inc_return(a)
+#define atomic_dec(a)		atomic_inc_return(a)
+
+#define atomic_dec_and_test(a)	(atomic_dec_return(a) == 0)
+
+#define cmpxchg(a, o, n)        uatomic_cmpxchg(a, o, n);
+
+static inline bool atomic_add_unless(atomic_t *a, int v, int u)
+{
+	int r = atomic_read(a);
+	int n, o;
+
+	do {
+		o = r;
+		if (o == u)
+			break;
+		n = o + v;
+		r = uatomic_cmpxchg(a, o, n);
+	} while (r != o);
+
+	return o != u;
+}
+
+static inline bool atomic_dec_and_lock(atomic_t *a, spinlock_t *lock)
+{
+	if (atomic_add_unless(a, -1, 1))
+		return 0;
+
+	spin_lock(lock);
+	if (atomic_dec_and_test(a))
+		return 1;
+	spin_unlock(lock);
+	return 0;
+}
 
-#define atomic64_read(x)	*(x)
-#define atomic64_set(x, v)	(*(x) = v)
+#define atomic64_read(x)	uatomic_read(x)
+#define atomic64_set(x, v)	uatomic_set(x, v)
 
 #endif /* __ATOMIC_H__ */
-- 
2.28.0


  parent reply index

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-15  7:21 [PATCH 00/27] [RFC, WIP] xfsprogs: xfs_buf unification and AIO Dave Chinner
2020-10-15  7:21 ` [PATCH 01/27] xfsprogs: remove unused buffer tracing code Dave Chinner
2020-10-15  7:21 ` [PATCH 02/27] xfsprogs: remove unused IO_DEBUG functionality Dave Chinner
2020-11-16  2:31   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 03/27] libxfs: get rid of b_bcount from xfs_buf Dave Chinner
2020-11-23 19:53   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 04/27] libxfs: rename buftarg->dev to btdev Dave Chinner
2020-11-16  2:33   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 05/27] xfsprogs: get rid of ancient btree tracing fragments Dave Chinner
2020-11-16  2:35   ` Eric Sandeen
2020-10-15  7:21 ` [PATCH 06/27] xfsprogs: remove xfs_buf_t typedef Dave Chinner
2020-10-15 15:22   ` Darrick J. Wong
2020-10-15 20:54     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 07/27] xfsprogs: introduce liburcu support Dave Chinner
2020-10-15  7:21 ` [PATCH 08/27] libxfs: add spinlock_t wrapper Dave Chinner
2020-10-15  7:21 ` Dave Chinner [this message]
2020-10-15  7:21 ` [PATCH 10/27] libxfs: add kernel-compatible completion API Dave Chinner
2020-10-15 17:09   ` Darrick J. Wong
2020-10-19 22:21     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 11/27] libxfs: add wrappers for kernel semaphores Dave Chinner
2020-10-15  7:21 ` [PATCH 12/27] xfsprogs: convert use-once buffer reads to uncached IO Dave Chinner
2020-10-15 17:12   ` Darrick J. Wong
2020-10-19 22:36     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 13/27] libxfs: introduce userspace buftarg infrastructure Dave Chinner
2020-10-15  7:21 ` [PATCH 14/27] xfs: rename libxfs_buftarg_init to libxfs_open_devices() Dave Chinner
2020-10-15  7:21 ` [PATCH 15/27] libxfs: introduce userspace buftarg infrastructure Dave Chinner
2020-10-15 17:16   ` Darrick J. Wong
2020-10-15  7:21 ` [PATCH 16/27] libxfs: add a synchronous IO engine to the buftarg Dave Chinner
2020-10-15  7:21 ` [PATCH 17/27] xfsprogs: convert libxfs_readbufr to libxfs_buf_read_uncached Dave Chinner
2020-10-15  7:21 ` [PATCH 18/27] libxfs: convert libxfs_bwrite to buftarg IO Dave Chinner
2020-10-15  7:21 ` [PATCH 19/27] libxfs: add cache infrastructure to buftarg Dave Chinner
2020-10-15  7:21 ` [PATCH 20/27] libxfs: add internal lru to btcache Dave Chinner
2020-10-15  7:21 ` [PATCH 21/27] libxfs: Add kernel list_lru wrapper Dave Chinner
2020-10-15  7:21 ` [PATCH 22/27] libxfs: introduce new buffer cache infrastructure Dave Chinner
2020-10-15 17:46   ` Darrick J. Wong
2020-10-15  7:21 ` [PATCH 23/27] libxfs: use PSI information to detect memory pressure Dave Chinner
2020-10-15 17:56   ` Darrick J. Wong
2020-10-15 21:20     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 24/27] libxfs: add a buftarg cache shrinker implementation Dave Chinner
2020-10-15 18:01   ` Darrick J. Wong
2020-10-15 21:33     ` Dave Chinner
2020-10-15  7:21 ` [PATCH 25/27] libxfs: switch buffer cache implementations Dave Chinner
2020-10-15  7:21 ` [PATCH 26/27] build: set platform_defs.h.in dependency correctly Dave Chinner
2020-10-15  7:21 ` [PATCH 27/27] libxfs: convert sync IO buftarg engine to AIO Dave Chinner
2020-10-15 18:26   ` Darrick J. Wong
2020-10-15 21:42     ` Dave Chinner
2020-10-15  7:29 ` [PATCH 00/27] [RFC, WIP] xfsprogs: xfs_buf unification and AIO Dave Chinner
2020-10-15 18:37 ` Darrick J. Wong
2020-10-15 22:35   ` Dave Chinner

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