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Groups > linux.kernel > #1521937
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [RFC][PATCH 7/7] kref: Implement using refcount_t |
| Date | 2016-11-14 18:50 +0100 |
| Message-ID | <sDtyi-1DM-23@gated-at.bofh.it> (permalink) |
| References | <sDtyh-1DM-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Provide refcount_t, an atomic_t like primitive built just for
refcounting.
It provides overflow and underflow checks as well as saturation
semantics such that when it overflows, we'll never attempt to free it
again, ever.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/kref.h | 29 ++----
include/linux/refcount.h | 221 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 232 insertions(+), 18 deletions(-)
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -15,16 +15,13 @@
#ifndef _KREF_H_
#define _KREF_H_
-#include <linux/bug.h>
-#include <linux/atomic.h>
-#include <linux/kernel.h>
-#include <linux/mutex.h>
+#include <linux/refcount.h>
struct kref {
- atomic_t refcount;
+ refcount_t refcount;
};
-#define KREF_INIT(n) { .refcount = ATOMIC_INIT(n), }
+#define KREF_INIT(n) { .refcount = REFCOUNT_INIT(n), }
/**
* kref_init - initialize object.
@@ -32,12 +29,12 @@ struct kref {
*/
static inline void kref_init(struct kref *kref)
{
- atomic_set(&kref->refcount, 1);
+ refcount_set(&kref->refcount, 1);
}
-static inline int kref_read(const struct kref *kref)
+static inline unsigned int kref_read(const struct kref *kref)
{
- return atomic_read(&kref->refcount);
+ return refcount_read(&kref->refcount);
}
/**
@@ -46,11 +43,7 @@ static inline int kref_read(const struct
*/
static inline void kref_get(struct kref *kref)
{
- /* If refcount was 0 before incrementing then we have a race
- * condition when this kref is freeing by some other thread right now.
- * In this case one should use kref_get_unless_zero()
- */
- WARN_ON_ONCE(atomic_inc_return(&kref->refcount) < 2);
+ refcount_inc(&kref->refcount);
}
/**
@@ -74,7 +67,7 @@ static inline int kref_put(struct kref *
{
WARN_ON(release == NULL);
- if (atomic_dec_and_test(&kref->refcount)) {
+ if (refcount_dec_and_test(&kref->refcount)) {
release(kref);
return 1;
}
@@ -87,7 +80,7 @@ static inline int kref_put_mutex(struct
{
WARN_ON(release == NULL);
- if (atomic_dec_and_mutex_lock(&kref->refcount, lock)) {
+ if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
release(kref);
return 1;
}
@@ -100,7 +93,7 @@ static inline int kref_put_lock(struct k
{
WARN_ON(release == NULL);
- if (atomic_dec_and_lock(&kref->refcount, lock)) {
+ if (refcount_dec_and_lock(&kref->refcount, lock)) {
release(kref);
return 1;
}
@@ -125,6 +118,6 @@ static inline int kref_put_lock(struct k
*/
static inline int __must_check kref_get_unless_zero(struct kref *kref)
{
- return atomic_add_unless(&kref->refcount, 1, 0);
+ return refcount_inc_not_zero(&kref->refcount);
}
#endif /* _KREF_H_ */
--- /dev/null
+++ b/include/linux/refcount.h
@@ -0,0 +1,221 @@
+#ifndef _LINUX_REFCOUNT_H
+#define _LINUX_REFCOUNT_H
+
+/*
+ * Variant of atomic_t specialized for refcounting.
+ *
+ * The interface matches the atomic_t interface (to aid in porting) but only
+ * provides the few functions one should use for refcounting.
+ *
+ * They add explicit overflow and underflow tests, once a refcount hits
+ * UINT_MAX it stays there.
+ *
+ * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
+ * and provide only what is strictly required for refcounts.
+ *
+ * The increments are fully relaxed; these will not provide ordering. The
+ * rationale is that whatever is used to obtain the object we're increasing the
+ * reference count on will provide the ordering. For locked data structures,
+ * its the lock acquire, for RCU/lockless data structures its the dependent
+ * read.
+ *
+ * Do note that inc_not_zero() provides a control dependency which will order
+ * future stores against the inc, this ensures we'll never modify the object
+ * if we did not in fact acquire a reference.
+ *
+ * The decrements will provide release order, such that all the prior loads and
+ * stores will be issued before we proceed with freeing the object.
+ *
+ */
+
+#include <linux/atomic.h>
+#include <linux/bug.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+
+typedef struct refcount_struct {
+ atomic_t refs;
+} refcount_t;
+
+#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
+
+static inline void refcount_set(refcount_t *r, int n)
+{
+ atomic_set(&r->refs, n);
+}
+
+static inline unsigned int refcount_read(const refcount_t *r)
+{
+ return atomic_read(&r->refs);
+}
+
+/*
+ * Similar to atomic_inc(), will BUG on overflow and saturate at UINT_MAX.
+ *
+ * Provides no memory ordering, it is assumed the caller already has a
+ * reference on the object, will WARN when this is not so.
+ */
+static inline void refcount_inc(refcount_t *r)
+{
+ unsigned int old, new, val = atomic_read(&r->refs);
+
+ for (;;) {
+ WARN_ON_ONCE(!val);
+
+ new = val + 1;
+ if (new < val)
+ BUG(); /* overflow */
+
+ old = atomic_cmpxchg_relaxed(&r->refs, val, new);
+ if (old == val)
+ break;
+
+ val = old;
+ }
+}
+
+/*
+ * Similar to atomic_inc_not_zero(), will BUG on overflow and saturate at UINT_MAX.
+ *
+ * Provides no memory ordering, it is assumed the caller has guaranteed the
+ * object memory to be stable (RCU, etc.). It does provide a control dependency
+ * and thereby orders future stores.
+ */
+static inline __must_check
+bool refcount_inc_not_zero(refcount_t *r)
+{
+ unsigned int old, new, val = atomic_read(&r->refs);
+
+ for (;;) {
+ if (!val)
+ return false;
+
+ new = val + 1;
+ if (new < val)
+ BUG(); /* overflow */
+
+ old = atomic_cmpxchg_relaxed(&r->refs, val, new);
+ if (old == val)
+ break;
+
+ val = old;
+ }
+
+ return true;
+}
+
+/*
+ * Similar to atomic_dec_and_test(), it will BUG on underflow and fail to
+ * decrement when saturated at UINT_MAX.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before a subsequent free.
+ */
+static inline __must_check
+bool refcount_dec_and_test(refcount_t *r)
+{
+ unsigned int old, new, val = atomic_read(&r->refs);
+
+ for (;;) {
+ if (val == UINT_MAX)
+ return false;
+
+ new = val - 1;
+ if (new > val)
+ BUG(); /* underflow */
+
+ old = atomic_cmpxchg_release(&r->refs, val, new);
+ if (old == val)
+ break;
+
+ val = old;
+ }
+
+ return !new;
+}
+
+/*
+ * Similar to atomic_dec_and_mutex_lock(), it will BUG on underflow and fail
+ * to decrement when saturated at UINT_MAX.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before a subsequent free. This allows free() while holding the mutex.
+ */
+static inline __must_check
+bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
+{
+ unsigned int old, new, val = atomic_read(&r->refs);
+ bool locked = false;
+
+ for (;;) {
+ if (val == UINT_MAX)
+ return false;
+
+ if (val == 1 && !locked) {
+ locked = true;
+ mutex_lock(lock);
+ }
+
+ new = val - 1;
+ if (new > val) {
+ if (locked)
+ mutex_unlock(lock);
+ BUG(); /* underflow */
+ }
+
+ old = atomic_cmpxchg_release(&r->refs, val, new);
+ if (old == val)
+ break;
+
+ val = old;
+ }
+
+ if (new && locked)
+ mutex_unlock(lock);
+
+ return !new;
+}
+
+/*
+ * Similar to atomic_dec_and_lock(), it will BUG on underflow and fail
+ * to decrement when saturated at UINT_MAX.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before a subsequent free. This allows free() while holding the lock.
+ */
+static inline __must_check
+bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
+{
+ unsigned int old, new, val = atomic_read(&r->refs);
+ bool locked = false;
+
+ for (;;) {
+ if (val == UINT_MAX)
+ return false;
+
+ if (val == 1 && !locked) {
+ locked = true;
+ spin_lock(lock);
+ }
+
+ new = val - 1;
+ if (new > val) {
+ if (locked)
+ spin_unlock(lock);
+ BUG(); /* underflow */
+ }
+
+ old = atomic_cmpxchg_release(&r->refs, val, new);
+ if (old == val)
+ break;
+
+ val = old;
+ }
+
+ if (new && locked)
+ spin_unlock(lock);
+
+ return !new;
+}
+
+#endif /* _LINUX_REFCOUNT_H */
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[RFC][PATCH 0/7] kref improvements Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
[RFC][PATCH 5/7] kref: Implement kref_put_lock() Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
Re: [RFC][PATCH 5/7] kref: Implement kref_put_lock() Kees Cook <keescook@chromium.org> - 2016-11-14 21:40 +0100
Re: [RFC][PATCH 5/7] kref: Implement kref_put_lock() Peter Zijlstra <peterz@infradead.org> - 2016-11-15 09:00 +0100
[RFC][PATCH 6/7] kref: Avoid more abuse Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
[RFC][PATCH 4/7] kref: Use kref_get_unless_zero() more Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
[RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-14 18:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-15 09:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 10:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-15 11:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 11:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-15 14:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-15 19:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 20:20 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-15 20:30 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-16 09:40 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 10:00 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-16 10:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 10:30 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-16 11:20 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-16 20:00 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 09:40 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-17 21:00 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Kees Cook <keescook@chromium.org> - 2016-11-16 19:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-15 13:40 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-15 14:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-15 15:20 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 10:30 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-17 10:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 11:40 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 11:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Greg KH <gregkh@linuxfoundation.org> - 2016-11-17 12:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:30 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-17 18:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-18 09:30 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-18 11:20 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-17 18:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:30 +0100
RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-18 11:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 12:40 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Will Deacon <will.deacon@arm.com> - 2016-11-18 18:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 20:00 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 05:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Ingo Molnar <mingo@kernel.org> - 2016-11-21 08:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 09:40 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 09:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-21 10:10 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Boqun Feng <boqun.feng@gmail.com> - 2016-11-21 10:40 +0100
RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-18 11:50 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 12:00 +0100
RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-18 18:00 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-18 20:00 +0100
RE: [RFC][PATCH 7/7] kref: Implement using refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-19 08:20 +0100
Re: [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra <peterz@infradead.org> - 2016-11-19 12:50 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Christoph Hellwig <hch@infradead.org> - 2016-11-14 19:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 08:30 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-15 08:50 +0100
[PATCH] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-15 09:40 +0100
[PATCH v2] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-15 09:50 +0100
Re: [PATCH v2] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' Peter Zijlstra <peterz@infradead.org> - 2016-11-15 10:30 +0100
[PATCH v3] printk, locking/atomics, kref: Introduce new %pAa and %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-15 10:50 +0100
Re: [PATCH v2] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' kbuild test robot <lkp@intel.com> - 2016-11-15 11:10 +0100
Re: [PATCH] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-15 17:50 +0100
Re: [PATCH] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' Ingo Molnar <mingo@kernel.org> - 2016-11-16 09:20 +0100
Re: [RFC][PATCH 0/7] kref improvements Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 08:30 +0100
Re: [RFC][PATCH 0/7] kref improvements Ingo Molnar <mingo@kernel.org> - 2016-11-15 08:50 +0100
Re: [RFC][PATCH 0/7] kref improvements Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 16:10 +0100
Re: [RFC][PATCH 0/7] kref improvements Peter Zijlstra <peterz@infradead.org> - 2016-11-15 08:50 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-15 08:40 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-15 09:10 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Kees Cook <keescook@chromium.org> - 2016-11-15 22:00 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 09:30 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-16 11:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 11:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Greg KH <gregkh@linuxfoundation.org> - 2016-11-16 11:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Daniel Borkmann <daniel@iogearbox.net> - 2016-11-16 11:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-16 11:10 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Kees Cook <keescook@chromium.org> - 2016-11-16 20:00 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 09:40 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() David Windsor <dave@progbits.org> - 2016-11-17 13:50 +0100
RE: [RFC][PATCH 2/7] kref: Add kref_read() "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-17 15:40 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:10 +0100
RE: [RFC][PATCH 2/7] kref: Add kref_read() "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-17 18:10 +0100
RE: [RFC][PATCH 2/7] kref: Add kref_read() "Reshetova, Elena" <elena.reshetova@intel.com> - 2016-11-17 19:10 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 20:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 20:40 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra <peterz@infradead.org> - 2016-11-17 18:20 +0100
Re: [RFC][PATCH 2/7] kref: Add kref_read() Kees Cook <keescook@chromium.org> - 2016-11-17 20:40 +0100
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