locking/refcounts: Out-of-line everything
Linus asked to please make this real C code. And since size then isn't an issue what so ever anymore, remove the debug knob and make all WARN()s unconditional. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dwindsor@gmail.com Cc: elena.reshetova@intel.com Cc: gregkh@linuxfoundation.org Cc: ishkamiel@gmail.com Cc: keescook@chromium.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
Ingo Molnar
parent
2bfe01eff4
commit
29dee3c03a
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@ -1,55 +1,10 @@
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#ifndef _LINUX_REFCOUNT_H
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#define _LINUX_REFCOUNT_H
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/*
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* Variant of atomic_t specialized for reference counts.
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*
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* The interface matches the atomic_t interface (to aid in porting) but only
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* provides the few functions one should use for reference counting.
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*
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* It differs in that the counter saturates at UINT_MAX and will not move once
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* there. This avoids wrapping the counter and causing 'spurious'
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* use-after-free issues.
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*
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* Memory ordering rules are slightly relaxed wrt regular atomic_t functions
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* and provide only what is strictly required for refcounts.
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*
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* The increments are fully relaxed; these will not provide ordering. The
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* rationale is that whatever is used to obtain the object we're increasing the
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* reference count on will provide the ordering. For locked data structures,
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* its the lock acquire, for RCU/lockless data structures its the dependent
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* load.
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*
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* Do note that inc_not_zero() provides a control dependency which will order
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* future stores against the inc, this ensures we'll never modify the object
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* if we did not in fact acquire a reference.
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*
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* The decrements will provide release order, such that all the prior loads and
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* stores will be issued before, it also provides a control dependency, which
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* will order us against the subsequent free().
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*
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* The control dependency is against the load of the cmpxchg (ll/sc) that
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* succeeded. This means the stores aren't fully ordered, but this is fine
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* because the 1->0 transition indicates no concurrency.
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*
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* Note that the allocator is responsible for ordering things between free()
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* and alloc().
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*
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*/
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#include <linux/atomic.h>
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#include <linux/bug.h>
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#include <linux/mutex.h>
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#include <linux/spinlock.h>
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#ifdef CONFIG_DEBUG_REFCOUNT
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#define REFCOUNT_WARN(cond, str) WARN_ON(cond)
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#define __refcount_check __must_check
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#else
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#define REFCOUNT_WARN(cond, str) (void)(cond)
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#define __refcount_check
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#endif
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typedef struct refcount_struct {
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atomic_t refs;
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} refcount_t;
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@ -66,229 +21,21 @@ static inline unsigned int refcount_read(const refcount_t *r)
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return atomic_read(&r->refs);
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}
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static inline __refcount_check
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bool refcount_add_not_zero(unsigned int i, refcount_t *r)
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{
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unsigned int old, new, val = atomic_read(&r->refs);
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extern __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r);
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extern void refcount_add(unsigned int i, refcount_t *r);
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for (;;) {
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if (!val)
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return false;
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extern __must_check bool refcount_inc_not_zero(refcount_t *r);
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extern void refcount_inc(refcount_t *r);
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if (unlikely(val == UINT_MAX))
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return true;
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extern __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r);
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extern void refcount_sub(unsigned int i, refcount_t *r);
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new = val + i;
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if (new < val)
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new = UINT_MAX;
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old = atomic_cmpxchg_relaxed(&r->refs, val, new);
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if (old == val)
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break;
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extern __must_check bool refcount_dec_and_test(refcount_t *r);
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extern void refcount_dec(refcount_t *r);
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val = old;
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}
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REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
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return true;
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}
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static inline void refcount_add(unsigned int i, refcount_t *r)
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{
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REFCOUNT_WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
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}
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/*
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* Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
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*
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* Provides no memory ordering, it is assumed the caller has guaranteed the
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* object memory to be stable (RCU, etc.). It does provide a control dependency
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* and thereby orders future stores. See the comment on top.
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*/
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static inline __refcount_check
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bool refcount_inc_not_zero(refcount_t *r)
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{
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unsigned int old, new, val = atomic_read(&r->refs);
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for (;;) {
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new = val + 1;
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if (!val)
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return false;
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if (unlikely(!new))
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return true;
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old = atomic_cmpxchg_relaxed(&r->refs, val, new);
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if (old == val)
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break;
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val = old;
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}
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REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
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return true;
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}
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/*
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* Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
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*
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* Provides no memory ordering, it is assumed the caller already has a
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* reference on the object, will WARN when this is not so.
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*/
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static inline void refcount_inc(refcount_t *r)
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{
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REFCOUNT_WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
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}
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/*
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* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
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* decrement when saturated at UINT_MAX.
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*
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* Provides release memory ordering, such that prior loads and stores are done
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* before, and provides a control dependency such that free() must come after.
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* See the comment on top.
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*/
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static inline __refcount_check
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bool refcount_sub_and_test(unsigned int i, refcount_t *r)
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{
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unsigned int old, new, val = atomic_read(&r->refs);
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for (;;) {
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if (unlikely(val == UINT_MAX))
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return false;
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new = val - i;
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if (new > val) {
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REFCOUNT_WARN(new > val, "refcount_t: underflow; use-after-free.\n");
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return false;
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}
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old = atomic_cmpxchg_release(&r->refs, val, new);
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if (old == val)
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break;
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val = old;
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}
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return !new;
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}
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static inline __refcount_check
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bool refcount_dec_and_test(refcount_t *r)
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{
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return refcount_sub_and_test(1, r);
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}
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/*
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* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
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* when saturated at UINT_MAX.
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*
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* Provides release memory ordering, such that prior loads and stores are done
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* before.
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*/
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static inline
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void refcount_dec(refcount_t *r)
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{
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REFCOUNT_WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
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}
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/*
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* No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
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* success thereof.
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*
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* Like all decrement operations, it provides release memory order and provides
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* a control dependency.
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*
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* It can be used like a try-delete operator; this explicit case is provided
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* and not cmpxchg in generic, because that would allow implementing unsafe
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* operations.
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*/
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static inline __refcount_check
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bool refcount_dec_if_one(refcount_t *r)
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{
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return atomic_cmpxchg_release(&r->refs, 1, 0) == 1;
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}
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/*
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* No atomic_t counterpart, it decrements unless the value is 1, in which case
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* it will return false.
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*
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* Was often done like: atomic_add_unless(&var, -1, 1)
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*/
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static inline __refcount_check
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bool refcount_dec_not_one(refcount_t *r)
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{
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unsigned int old, new, val = atomic_read(&r->refs);
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for (;;) {
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if (unlikely(val == UINT_MAX))
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return true;
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if (val == 1)
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return false;
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new = val - 1;
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if (new > val) {
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REFCOUNT_WARN(new > val, "refcount_t: underflow; use-after-free.\n");
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return true;
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}
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old = atomic_cmpxchg_release(&r->refs, val, new);
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if (old == val)
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break;
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val = old;
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}
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return true;
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}
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/*
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* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
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* to decrement when saturated at UINT_MAX.
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*
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* Provides release memory ordering, such that prior loads and stores are done
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* before, and provides a control dependency such that free() must come after.
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* See the comment on top.
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*/
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static inline __refcount_check
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bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
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{
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if (refcount_dec_not_one(r))
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return false;
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mutex_lock(lock);
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if (!refcount_dec_and_test(r)) {
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mutex_unlock(lock);
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return false;
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}
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return true;
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}
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/*
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* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
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* decrement when saturated at UINT_MAX.
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*
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* Provides release memory ordering, such that prior loads and stores are done
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* before, and provides a control dependency such that free() must come after.
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* See the comment on top.
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*/
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static inline __refcount_check
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bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
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{
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if (refcount_dec_not_one(r))
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return false;
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spin_lock(lock);
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if (!refcount_dec_and_test(r)) {
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spin_unlock(lock);
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return false;
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}
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return true;
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}
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extern __must_check bool refcount_dec_if_one(refcount_t *r);
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extern __must_check bool refcount_dec_not_one(refcount_t *r);
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extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock);
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extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock);
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#endif /* _LINUX_REFCOUNT_H */
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@ -716,19 +716,6 @@ source "lib/Kconfig.kmemcheck"
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source "lib/Kconfig.kasan"
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config DEBUG_REFCOUNT
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bool "Verbose refcount checks"
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help
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Say Y here if you want reference counters (refcount_t and kref) to
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generate WARNs on dubious usage. Without this refcount_t will still
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be a saturating counter and avoid Use-After-Free by turning it into
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a resource leak Denial-Of-Service.
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Use of this option will increase kernel text size but will alert the
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admin of potential abuse.
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If in doubt, say "N".
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endmenu # "Memory Debugging"
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config ARCH_HAS_KCOV
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@ -36,7 +36,7 @@ obj-y += bcd.o div64.o sort.o parser.o debug_locks.o random32.o \
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gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
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bsearch.o find_bit.o llist.o memweight.o kfifo.o \
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percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \
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once.o
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once.o refcount.o
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obj-y += string_helpers.o
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obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
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obj-y += hexdump.o
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@ -0,0 +1,267 @@
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/*
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* Variant of atomic_t specialized for reference counts.
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*
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* The interface matches the atomic_t interface (to aid in porting) but only
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* provides the few functions one should use for reference counting.
|
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*
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* It differs in that the counter saturates at UINT_MAX and will not move once
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* there. This avoids wrapping the counter and causing 'spurious'
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* use-after-free issues.
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*
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* Memory ordering rules are slightly relaxed wrt regular atomic_t functions
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* and provide only what is strictly required for refcounts.
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*
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* The increments are fully relaxed; these will not provide ordering. The
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* rationale is that whatever is used to obtain the object we're increasing the
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* reference count on will provide the ordering. For locked data structures,
|
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* its the lock acquire, for RCU/lockless data structures its the dependent
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* load.
|
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*
|
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* Do note that inc_not_zero() provides a control dependency which will order
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* future stores against the inc, this ensures we'll never modify the object
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* if we did not in fact acquire a reference.
|
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*
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* The decrements will provide release order, such that all the prior loads and
|
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* stores will be issued before, it also provides a control dependency, which
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* will order us against the subsequent free().
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*
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* The control dependency is against the load of the cmpxchg (ll/sc) that
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* succeeded. This means the stores aren't fully ordered, but this is fine
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* because the 1->0 transition indicates no concurrency.
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*
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* Note that the allocator is responsible for ordering things between free()
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* and alloc().
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*
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*/
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#include <linux/refcount.h>
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#include <linux/bug.h>
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bool refcount_add_not_zero(unsigned int i, refcount_t *r)
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{
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unsigned int old, new, val = atomic_read(&r->refs);
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for (;;) {
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if (!val)
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return false;
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if (unlikely(val == UINT_MAX))
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return true;
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new = val + i;
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if (new < val)
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new = UINT_MAX;
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old = atomic_cmpxchg_relaxed(&r->refs, val, new);
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if (old == val)
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break;
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val = old;
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}
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WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
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return true;
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}
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EXPORT_SYMBOL_GPL(refcount_add_not_zero);
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void refcount_add(unsigned int i, refcount_t *r)
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{
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WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
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}
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EXPORT_SYMBOL_GPL(refcount_add);
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/*
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* Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
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*
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* Provides no memory ordering, it is assumed the caller has guaranteed the
|
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* object memory to be stable (RCU, etc.). It does provide a control dependency
|
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* and thereby orders future stores. See the comment on top.
|
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*/
|
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bool refcount_inc_not_zero(refcount_t *r)
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{
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unsigned int old, new, val = atomic_read(&r->refs);
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for (;;) {
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new = val + 1;
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if (!val)
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return false;
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if (unlikely(!new))
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return true;
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old = atomic_cmpxchg_relaxed(&r->refs, val, new);
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if (old == val)
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break;
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val = old;
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}
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WARN(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
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return true;
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}
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EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
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/*
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* Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
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*
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* Provides no memory ordering, it is assumed the caller already has a
|
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* reference on the object, will WARN when this is not so.
|
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*/
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void refcount_inc(refcount_t *r)
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{
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WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
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}
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EXPORT_SYMBOL_GPL(refcount_inc);
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bool refcount_sub_and_test(unsigned int i, refcount_t *r)
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{
|
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unsigned int old, new, val = atomic_read(&r->refs);
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|
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for (;;) {
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if (unlikely(val == UINT_MAX))
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return false;
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new = val - i;
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if (new > val) {
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WARN(new > val, "refcount_t: underflow; use-after-free.\n");
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return false;
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}
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old = atomic_cmpxchg_release(&r->refs, val, new);
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if (old == val)
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break;
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val = old;
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}
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return !new;
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}
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EXPORT_SYMBOL_GPL(refcount_sub_and_test);
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|
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/*
|
||||
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
|
||||
* decrement when saturated at UINT_MAX.
|
||||
*
|
||||
* Provides release memory ordering, such that prior loads and stores are done
|
||||
* before, and provides a control dependency such that free() must come after.
|
||||
* See the comment on top.
|
||||
*/
|
||||
bool refcount_dec_and_test(refcount_t *r)
|
||||
{
|
||||
return refcount_sub_and_test(1, r);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(refcount_dec_and_test);
|
||||
|
||||
/*
|
||||
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
|
||||
* when saturated at UINT_MAX.
|
||||
*
|
||||
* Provides release memory ordering, such that prior loads and stores are done
|
||||
* before.
|
||||
*/
|
||||
|
||||
void refcount_dec(refcount_t *r)
|
||||
{
|
||||
WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(refcount_dec);
|
||||
|
||||
/*
|
||||
* No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
|
||||
* success thereof.
|
||||
*
|
||||
* Like all decrement operations, it provides release memory order and provides
|
||||
* a control dependency.
|
||||
*
|
||||
* It can be used like a try-delete operator; this explicit case is provided
|
||||
* and not cmpxchg in generic, because that would allow implementing unsafe
|
||||
* operations.
|
||||
*/
|
||||
bool refcount_dec_if_one(refcount_t *r)
|
||||
{
|
||||
return atomic_cmpxchg_release(&r->refs, 1, 0) == 1;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(refcount_dec_if_one);
|
||||
|
||||
/*
|
||||
* No atomic_t counterpart, it decrements unless the value is 1, in which case
|
||||
* it will return false.
|
||||
*
|
||||
* Was often done like: atomic_add_unless(&var, -1, 1)
|
||||
*/
|
||||
bool refcount_dec_not_one(refcount_t *r)
|
||||
{
|
||||
unsigned int old, new, val = atomic_read(&r->refs);
|
||||
|
||||
for (;;) {
|
||||
if (unlikely(val == UINT_MAX))
|
||||
return true;
|
||||
|
||||
if (val == 1)
|
||||
return false;
|
||||
|
||||
new = val - 1;
|
||||
if (new > val) {
|
||||
WARN(new > val, "refcount_t: underflow; use-after-free.\n");
|
||||
return true;
|
||||
}
|
||||
|
||||
old = atomic_cmpxchg_release(&r->refs, val, new);
|
||||
if (old == val)
|
||||
break;
|
||||
|
||||
val = old;
|
||||
}
|
||||
|
||||
return true;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(refcount_dec_not_one);
|
||||
|
||||
/*
|
||||
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
|
||||
* to decrement when saturated at UINT_MAX.
|
||||
*
|
||||
* Provides release memory ordering, such that prior loads and stores are done
|
||||
* before, and provides a control dependency such that free() must come after.
|
||||
* See the comment on top.
|
||||
*/
|
||||
bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
|
||||
{
|
||||
if (refcount_dec_not_one(r))
|
||||
return false;
|
||||
|
||||
mutex_lock(lock);
|
||||
if (!refcount_dec_and_test(r)) {
|
||||
mutex_unlock(lock);
|
||||
return false;
|
||||
}
|
||||
|
||||
return true;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(refcount_dec_and_mutex_lock);
|
||||
|
||||
/*
|
||||
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
|
||||
* decrement when saturated at UINT_MAX.
|
||||
*
|
||||
* Provides release memory ordering, such that prior loads and stores are done
|
||||
* before, and provides a control dependency such that free() must come after.
|
||||
* See the comment on top.
|
||||
*/
|
||||
bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
|
||||
{
|
||||
if (refcount_dec_not_one(r))
|
||||
return false;
|
||||
|
||||
spin_lock(lock);
|
||||
if (!refcount_dec_and_test(r)) {
|
||||
spin_unlock(lock);
|
||||
return false;
|
||||
}
|
||||
|
||||
return true;
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(refcount_dec_and_lock);
|
||||
|
||||
Loading…
Reference in New Issue