History

tools include: Adopt kernel's refcount.h

To aid in catching bugs when using atomics as a reference count. This is a trimmed down version with just what is used by tools/ at this point. After this, the patches submitted by Elena for tools/ doing the conversion from atomic_ to recount_ methods can be applied and tested. To activate it, buint perf with: make DEBUG=1 -C tools/perf

Arnaldo Carvalho de Melo committed 9 years ago

Commit 73a9bf91 parent eaa75b52 files · +152 −0Browse files

Unified · Split

2 files
  1. tools/include/linux/refcount.h +151 −0
  2. tools/perf/MANIFEST +1 −0
tools/include/linux/refcount.h+151−0
@@ -0,0 +1,151 @@
1+#ifndef _TOOLS_LINUX_REFCOUNT_H
2+#define _TOOLS_LINUX_REFCOUNT_H
3+
4+/*
5+ * Variant of atomic_t specialized for reference counts.
6+ *
7+ * The interface matches the atomic_t interface (to aid in porting) but only
8+ * provides the few functions one should use for reference counting.
9+ *
10+ * It differs in that the counter saturates at UINT_MAX and will not move once
11+ * there. This avoids wrapping the counter and causing 'spurious'
12+ * use-after-free issues.
13+ *
14+ * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
15+ * and provide only what is strictly required for refcounts.
16+ *
17+ * The increments are fully relaxed; these will not provide ordering. The
18+ * rationale is that whatever is used to obtain the object we're increasing the
19+ * reference count on will provide the ordering. For locked data structures,
20+ * its the lock acquire, for RCU/lockless data structures its the dependent
21+ * load.
22+ *
23+ * Do note that inc_not_zero() provides a control dependency which will order
24+ * future stores against the inc, this ensures we'll never modify the object
25+ * if we did not in fact acquire a reference.
26+ *
27+ * The decrements will provide release order, such that all the prior loads and
28+ * stores will be issued before, it also provides a control dependency, which
29+ * will order us against the subsequent free().
30+ *
31+ * The control dependency is against the load of the cmpxchg (ll/sc) that
32+ * succeeded. This means the stores aren't fully ordered, but this is fine
33+ * because the 1->0 transition indicates no concurrency.
34+ *
35+ * Note that the allocator is responsible for ordering things between free()
36+ * and alloc().
37+ *
38+ */
39+
40+#include <linux/atomic.h>
41+#include <linux/kernel.h>
42+
43+#ifdef NDEBUG
44+#define REFCOUNT_WARN(cond, str) (void)(cond)
45+#define __refcount_check
46+#else
47+#define REFCOUNT_WARN(cond, str) BUG_ON(cond)
48+#define __refcount_check __must_check
49+#endif
50+
51+typedef struct refcount_struct {
52+ atomic_t refs;
53+} refcount_t;
54+
55+#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
56+
57+static inline void refcount_set(refcount_t *r, unsigned int n)
58+{
59+ atomic_set(&r->refs, n);
60+}
61+
62+static inline unsigned int refcount_read(const refcount_t *r)
63+{
64+ return atomic_read(&r->refs);
65+}
66+
67+/*
68+ * Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
69+ *
70+ * Provides no memory ordering, it is assumed the caller has guaranteed the
71+ * object memory to be stable (RCU, etc.). It does provide a control dependency
72+ * and thereby orders future stores. See the comment on top.
73+ */
74+static inline __refcount_check
75+bool refcount_inc_not_zero(refcount_t *r)
76+{
77+ unsigned int old, new, val = atomic_read(&r->refs);
78+
79+ for (;;) {
80+ new = val + 1;
81+
82+ if (!val)
83+ return false;
84+
85+ if (unlikely(!new))
86+ return true;
87+
88+ old = atomic_cmpxchg_relaxed(&r->refs, val, new);
89+ if (old == val)
90+ break;
91+
92+ val = old;
93+ }
94+
95+ REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
96+
97+ return true;
98+}
99+
100+/*
101+ * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
102+ *
103+ * Provides no memory ordering, it is assumed the caller already has a
104+ * reference on the object, will WARN when this is not so.
105+ */
106+static inline void refcount_inc(refcount_t *r)
107+{
108+ REFCOUNT_WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
109+}
110+
111+/*
112+ * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
113+ * decrement when saturated at UINT_MAX.
114+ *
115+ * Provides release memory ordering, such that prior loads and stores are done
116+ * before, and provides a control dependency such that free() must come after.
117+ * See the comment on top.
118+ */
119+static inline __refcount_check
120+bool refcount_sub_and_test(unsigned int i, refcount_t *r)
121+{
122+ unsigned int old, new, val = atomic_read(&r->refs);
123+
124+ for (;;) {
125+ if (unlikely(val == UINT_MAX))
126+ return false;
127+
128+ new = val - i;
129+ if (new > val) {
130+ REFCOUNT_WARN(new > val, "refcount_t: underflow; use-after-free.\n");
131+ return false;
132+ }
133+
134+ old = atomic_cmpxchg_release(&r->refs, val, new);
135+ if (old == val)
136+ break;
137+
138+ val = old;
139+ }
140+
141+ return !new;
142+}
143+
144+static inline __refcount_check
145+bool refcount_dec_and_test(refcount_t *r)
146+{
147+ return refcount_sub_and_test(1, r);
148+}
149+
150+
151+#endif /* _ATOMIC_LINUX_REFCOUNT_H */
tools/perf/MANIFEST+1−0
@@ -79,6 +79,7 @@ tools/include/uapi/linux/perf_event.h · 78 unmodified lines
7979 tools/include/linux/poison.h
8080 tools/include/linux/rbtree.h
8181 tools/include/linux/rbtree_augmented.h
82+tools/include/linux/refcount.h
8283 tools/include/linux/string.h
8384 tools/include/linux/stringify.h
8485 tools/include/linux/types.h

Keyboard shortcuts

General

Show keyboard shortcuts
?
Focus the current search
/

Issues and pull requests

Open filters
f

Issues, pull requests and Inbox

Select next item
j↓
Select previous item
k↑
Open selected item
Enter
Dismiss filters or clear selection
Esc

Repository code

Go to file
t