linux-kernel - Re: [tip:locking/core] locking/refcount: Create unchecked atomic

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Date:   Mon, 4 Sep 2017 14:37:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     davem@...emloft.net, arnd@...db.de, manfred@...orfullife.com,
        riel@...hat.com, hpa@...or.com, ebiggers3@...il.com,
        elena.reshetova@...el.com, keescook@...omium.org,
        dwindsor@...il.com, mingo@...nel.org, jannh@...gle.com,
        serge@...lyn.com, adobriyan@...il.com, gregkh@...uxfoundation.org,
        ebiederm@...ssion.com, ishkamiel@...il.com, tglx@...utronix.de,
        hch@...radead.org, jpoimboe@...hat.com,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        akpm@...ux-foundation.org, dave@...olabs.net,
        linux-arch@...r.kernel.org, James.Bottomley@...senpartnership.com
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:locking/core] locking/refcount: Create unchecked atomic_t
 implementation

On Wed, Jun 28, 2017 at 09:58:15AM -0700, tip-bot for Kees Cook wrote:
> locking/refcount: Create unchecked atomic_t implementation

This seems to do only half the job. Here's the rest.

---
Subject: locking/refcount: Finish unchecked atomic_t implementation

For some reason the unchecked atomic_t implementation stopped half-way
through, complete it it.

Fixes: fd25d19f6b8d ("locking/refcount: Create unchecked atomic_t implementation")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/linux/refcount.h | 35 ++++++++++++++++++++++++++++++-----
 lib/Makefile             |  7 +++----
 lib/refcount.c           |  3 ---
 3 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 48b7c9c68c4d..ef714e4347d9 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -52,10 +52,17 @@ extern __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r);
 
 extern __must_check bool refcount_dec_and_test(refcount_t *r);
 extern void refcount_dec(refcount_t *r);
+
+extern __must_check bool refcount_dec_if_one(refcount_t *r);
+extern __must_check bool refcount_dec_not_one(refcount_t *r);
+extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock);
+extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock);
+
 #else
 # ifdef CONFIG_ARCH_HAS_REFCOUNT
 #  include <asm/refcount.h>
 # else
+
 static inline __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r)
 {
 	return atomic_add_unless(&r->refs, i, 0);
@@ -90,12 +97,30 @@ static inline void refcount_dec(refcount_t *r)
 {
 	atomic_dec(&r->refs);
 }
+
+static inline __must_check bool refcount_dec_if_one(refcount_t *r)
+{
+	int val = 1;
+
+	return atomic_try_cmpxchg_release(&r->refs, &val, 0);
+}
+
+static inline __must_check bool refcount_dec_not_one(refcount_t *r)
+{
+	return atomic_add_unless(&r->refs, -1, 1);
+}
+
+static inline __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
+{
+	return atomic_dec_and_mutex_lock(&r->refs, lock);
+}
+
+static inline __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
+{
+	return atomic_dec_and_lock(&r->refs, lock);
+}
+
 # endif /* !CONFIG_ARCH_HAS_REFCOUNT */
 #endif /* CONFIG_REFCOUNT_FULL */
 
-extern __must_check bool refcount_dec_if_one(refcount_t *r);
-extern __must_check bool refcount_dec_not_one(refcount_t *r);
-extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock);
-extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock);
-
 #endif /* _LINUX_REFCOUNT_H */
diff --git a/lib/Makefile b/lib/Makefile
index 40c18372b301..b96859e69c57 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -38,12 +38,11 @@ obj-y += bcd.o div64.o sort.o parser.o debug_locks.o random32.o \
 	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
 	 bsearch.o find_bit.o llist.o memweight.o kfifo.o \
 	 percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \
-	 once.o refcount.o usercopy.o errseq.o
-obj-y += string_helpers.o
+	 once.o usercopy.o errseq.o string_helpers.o hexdump.o kstrtox.o
+
+obj-$(CONFIG_REFCOUNT_FULL) += refcount.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
-obj-y += hexdump.o
 obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
-obj-y += kstrtox.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
 obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
 obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
diff --git a/lib/refcount.c b/lib/refcount.c
index 5d0582a9480c..9f906783987e 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -37,8 +37,6 @@
 #include <linux/refcount.h>
 #include <linux/bug.h>
 
-#ifdef CONFIG_REFCOUNT_FULL
-
 /**
  * refcount_add_not_zero - add a value to a refcount unless it is 0
  * @i: the value to add to the refcount
@@ -227,7 +225,6 @@ void refcount_dec(refcount_t *r)
 	WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
 }
 EXPORT_SYMBOL(refcount_dec);
-#endif /* CONFIG_REFCOUNT_FULL */
 
 /**
  * refcount_dec_if_one - decrement a refcount if it is 1