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locking/refcount: Define constants for saturation and max refcount values

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[ Upstream commit 23e6b169c9917fbd77534f8c5f378cb073f548bd ]

The REFCOUNT_FULL implementation uses a different saturation point than
the x86 implementation, which means that the shared refcount code in
lib/refcount.c (e.g. refcount_dec_not_one()) needs to be aware of the
difference.

Rather than duplicate the definitions from the lkdtm driver, instead
move them into <linux/refcount.h> and update all references accordingly.

Signed-off-by: Will Deacon <[email protected]>
Reviewed-by: Ard Biesheuvel <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Tested-by: Hanjun Guo <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Elena Reshetova <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Will Deacon 2019-11-21 11:58:53 +00:00 • committed by Greg Kroah-Hartman
commit 68b4ee68e8
3 changed files with 29 additions and 26 deletions
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37
lib/refcount.c
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@ -5,8 +5,8 @@
* The interface matches the atomic_t interface (to aid in porting) but only
* provides the few functions one should use for reference counting.
*
* It differs in that the counter saturates at UINT_MAX and will not move once
* there. This avoids wrapping the counter and causing 'spurious'
* It differs in that the counter saturates at REFCOUNT_SATURATED and will not
* move once there. This avoids wrapping the counter and causing 'spurious'
* use-after-free issues.
*
* Memory ordering rules are slightly relaxed wrt regular atomic_t functions
@ -48,7 +48,7 @@
* @i: the value to add to the refcount
* @r: the refcount
*
* Will saturate at UINT_MAX and WARN.
* Will saturate at REFCOUNT_SATURATED and WARN.
*
* 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
@ -69,16 +69,17 @@ bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r)
if (!val)
return false;
if (unlikely(val == UINT_MAX))
if (unlikely(val == REFCOUNT_SATURATED))
return true;
new = val + i;
if (new < val)
new = UINT_MAX;
new = REFCOUNT_SATURATED;
} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
WARN_ONCE(new == REFCOUNT_SATURATED,
"refcount_t: saturated; leaking memory.\n");
return true;
}
@ -89,7 +90,7 @@ EXPORT_SYMBOL(refcount_add_not_zero_checked);
* @i: the value to add to the refcount
* @r: the refcount
*
* Similar to atomic_add(), but will saturate at UINT_MAX and WARN.
* Similar to atomic_add(), but will saturate at REFCOUNT_SATURATED and WARN.
*
* 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
@ -110,7 +111,8 @@ EXPORT_SYMBOL(refcount_add_checked);
* refcount_inc_not_zero_checked - increment a refcount unless it is 0
* @r: the refcount to increment
*
* Similar to atomic_inc_not_zero(), but will saturate at UINT_MAX and WARN.
* Similar to atomic_inc_not_zero(), but will saturate at REFCOUNT_SATURATED
* and WARN.
*
* 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
@ -133,7 +135,8 @@ bool refcount_inc_not_zero_checked(refcount_t *r)
} while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new));
WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n");
WARN_ONCE(new == REFCOUNT_SATURATED,
"refcount_t: saturated; leaking memory.\n");
return true;
}
@ -143,7 +146,7 @@ EXPORT_SYMBOL(refcount_inc_not_zero_checked);
* refcount_inc_checked - increment a refcount
* @r: the refcount to increment
*
* Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.
* Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN.
*
* Provides no memory ordering, it is assumed the caller already has a
* reference on the object.
@ -164,7 +167,7 @@ EXPORT_SYMBOL(refcount_inc_checked);
*
* Similar to atomic_dec_and_test(), but it will WARN, return false and
* ultimately leak on underflow and will fail to decrement when saturated
* at UINT_MAX.
* at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides an acquire ordering on success such that free()
@ -182,7 +185,7 @@ bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);
do {
if (unlikely(val == UINT_MAX))
if (unlikely(val == REFCOUNT_SATURATED))
return false;
new = val - i;
@ -207,7 +210,7 @@ EXPORT_SYMBOL(refcount_sub_and_test_checked);
* @r: the refcount
*
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
* decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides an acquire ordering on success such that free()
@ -226,7 +229,7 @@ EXPORT_SYMBOL(refcount_dec_and_test_checked);
* @r: the refcount
*
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
* when saturated at UINT_MAX.
* when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before.
@ -277,7 +280,7 @@ bool refcount_dec_not_one(refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);
do {
if (unlikely(val == UINT_MAX))
if (unlikely(val == REFCOUNT_SATURATED))
return true;
if (val == 1)
@ -302,7 +305,7 @@ EXPORT_SYMBOL(refcount_dec_not_one);
* @lock: the mutex to be locked
*
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
* to decrement when saturated at UINT_MAX.
* to decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
@ -333,7 +336,7 @@ EXPORT_SYMBOL(refcount_dec_and_mutex_lock);
* @lock: the spinlock to be locked
*
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
* decrement when saturated at REFCOUNT_SATURATED.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.