diff options
author | Thomas Bertschinger <tahbertschinger@gmail.com> | 2024-01-15 23:41:02 -0700 |
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committer | Kent Overstreet <kent.overstreet@linux.dev> | 2024-01-16 01:47:05 -0500 |
commit | f5baaf48e3e82b1caf9f5cd1207d4d6feba3a2e5 (patch) | |
tree | 59f7b0e4667df7a9d3d5a45725f2aaab3e79b4c5 /include/linux/refcount.h | |
parent | fb35dbfdc5a9446fbb856dae5542b23963e28b89 (diff) |
move Rust sources to top level, C sources into c_src
This moves the Rust sources out of rust_src/ and into the top level.
Running the bcachefs executable out of the development tree is now:
$ ./target/release/bcachefs command
or
$ cargo run --profile release -- command
instead of "./bcachefs command".
Building and installing is still:
$ make && make install
Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Diffstat (limited to 'include/linux/refcount.h')
-rw-r--r-- | include/linux/refcount.h | 352 |
1 files changed, 0 insertions, 352 deletions
diff --git a/include/linux/refcount.h b/include/linux/refcount.h deleted file mode 100644 index ddeec986..00000000 --- a/include/linux/refcount.h +++ /dev/null @@ -1,352 +0,0 @@ -/* SPDX-License-Identifier: GPL-2.0 */ -/* - * Variant of atomic_t specialized for reference counts. - * - * The interface matches the atomic_t interface (to aid in porting) but only - * provides the few functions one should use for reference counting. - * - * Saturation semantics - * ==================== - * - * refcount_t differs from atomic_t 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. In order to avoid the - * cost associated with introducing cmpxchg() loops into all of the saturating - * operations, we temporarily allow the counter to take on an unchecked value - * and then explicitly set it to REFCOUNT_SATURATED on detecting that underflow - * or overflow has occurred. Although this is racy when multiple threads - * access the refcount concurrently, by placing REFCOUNT_SATURATED roughly - * equidistant from 0 and INT_MAX we minimise the scope for error: - * - * INT_MAX REFCOUNT_SATURATED UINT_MAX - * 0 (0x7fff_ffff) (0xc000_0000) (0xffff_ffff) - * +--------------------------------+----------------+----------------+ - * <---------- bad value! ----------> - * - * (in a signed view of the world, the "bad value" range corresponds to - * a negative counter value). - * - * As an example, consider a refcount_inc() operation that causes the counter - * to overflow: - * - * int old = atomic_fetch_add_relaxed(r); - * // old is INT_MAX, refcount now INT_MIN (0x8000_0000) - * if (old < 0) - * atomic_set(r, REFCOUNT_SATURATED); - * - * If another thread also performs a refcount_inc() operation between the two - * atomic operations, then the count will continue to edge closer to 0. If it - * reaches a value of 1 before /any/ of the threads reset it to the saturated - * value, then a concurrent refcount_dec_and_test() may erroneously free the - * underlying object. - * Linux limits the maximum number of tasks to PID_MAX_LIMIT, which is currently - * 0x400000 (and can't easily be raised in the future beyond FUTEX_TID_MASK). - * With the current PID limit, if no batched refcounting operations are used and - * the attacker can't repeatedly trigger kernel oopses in the middle of refcount - * operations, this makes it impossible for a saturated refcount to leave the - * saturation range, even if it is possible for multiple uses of the same - * refcount to nest in the context of a single task: - * - * (UINT_MAX+1-REFCOUNT_SATURATED) / PID_MAX_LIMIT = - * 0x40000000 / 0x400000 = 0x100 = 256 - * - * If hundreds of references are added/removed with a single refcounting - * operation, it may potentially be possible to leave the saturation range; but - * given the precise timing details involved with the round-robin scheduling of - * each thread manipulating the refcount and the need to hit the race multiple - * times in succession, there doesn't appear to be a practical avenue of attack - * even if using refcount_add() operations with larger increments. - * - * Memory ordering - * =============== - * - * 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 - * load. - * - * 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, it also provides a control dependency, which - * will order us against the subsequent free(). - * - * The control dependency is against the load of the cmpxchg (ll/sc) that - * succeeded. This means the stores aren't fully ordered, but this is fine - * because the 1->0 transition indicates no concurrency. - * - * Note that the allocator is responsible for ordering things between free() - * and alloc(). - * - * The decrements dec_and_test() and sub_and_test() also provide acquire - * ordering on success. - * - */ - -#ifndef _LINUX_REFCOUNT_H -#define _LINUX_REFCOUNT_H - -#include <linux/atomic.h> -#include <linux/bug.h> -#include <linux/compiler.h> -#include <linux/limits.h> - -struct mutex; - -/** - * typedef refcount_t - variant of atomic_t specialized for reference counts - * @refs: atomic_t counter field - * - * The counter saturates at REFCOUNT_SATURATED and will not move once - * there. This avoids wrapping the counter and causing 'spurious' - * use-after-free bugs. - */ -typedef struct refcount_struct { - atomic_t refs; -} refcount_t; - -#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), } -#define REFCOUNT_MAX INT_MAX -#define REFCOUNT_SATURATED (INT_MIN / 2) - -enum refcount_saturation_type { - REFCOUNT_ADD_NOT_ZERO_OVF, - REFCOUNT_ADD_OVF, - REFCOUNT_ADD_UAF, - REFCOUNT_SUB_UAF, - REFCOUNT_DEC_LEAK, -}; - -/** - * refcount_set - set a refcount's value - * @r: the refcount - * @n: value to which the refcount will be set - */ -static inline void refcount_set(refcount_t *r, int n) -{ - atomic_set(&r->refs, n); -} - -/** - * refcount_read - get a refcount's value - * @r: the refcount - * - * Return: the refcount's value - */ -static inline unsigned int refcount_read(const refcount_t *r) -{ - return atomic_read(&r->refs); -} - -static inline __must_check bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp) -{ - int old = refcount_read(r); - - do { - if (!old) - break; - } while (!atomic_try_cmpxchg_acquire(&r->refs, &old, old + i)); - - if (oldp) - *oldp = old; - - return old; -} - -/** - * refcount_add_not_zero - add a value to a refcount unless it is 0 - * @i: the value to add to the refcount - * @r: the refcount - * - * 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 - * and thereby orders future stores. See the comment on top. - * - * Use of this function is not recommended for the normal reference counting - * use case in which references are taken and released one at a time. In these - * cases, refcount_inc(), or one of its variants, should instead be used to - * increment a reference count. - * - * Return: false if the passed refcount is 0, true otherwise - */ -static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r) -{ - return __refcount_add_not_zero(i, r, NULL); -} - -static inline void __refcount_add(int i, refcount_t *r, int *oldp) -{ - int old = atomic_add_return(i, &r->refs); - - if (oldp) - *oldp = old; -} - -/** - * refcount_add - add a value to a refcount - * @i: the value to add to the refcount - * @r: the refcount - * - * 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 - * and thereby orders future stores. See the comment on top. - * - * Use of this function is not recommended for the normal reference counting - * use case in which references are taken and released one at a time. In these - * cases, refcount_inc(), or one of its variants, should instead be used to - * increment a reference count. - */ -static inline void refcount_add(int i, refcount_t *r) -{ - __refcount_add(i, r, NULL); -} - -static inline __must_check bool __refcount_inc_not_zero(refcount_t *r, int *oldp) -{ - return __refcount_add_not_zero(1, r, oldp); -} - -/** - * refcount_inc_not_zero - increment a refcount unless it is 0 - * @r: the refcount to increment - * - * 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 - * and thereby orders future stores. See the comment on top. - * - * Return: true if the increment was successful, false otherwise - */ -static inline __must_check bool refcount_inc_not_zero(refcount_t *r) -{ - return __refcount_inc_not_zero(r, NULL); -} - -static inline void __refcount_inc(refcount_t *r, int *oldp) -{ - __refcount_add(1, r, oldp); -} - -/** - * refcount_inc - increment a refcount - * @r: the refcount to increment - * - * 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. - * - * Will WARN if the refcount is 0, as this represents a possible use-after-free - * condition. - */ -static inline void refcount_inc(refcount_t *r) -{ - __refcount_inc(r, NULL); -} - -static inline __must_check bool __refcount_sub_and_test(int i, refcount_t *r, int *oldp) -{ - int old = atomic_sub_return_release(i, &r->refs); - - if (oldp) - *oldp = old; - - if (old == i) { - smp_acquire__after_ctrl_dep(); - return true; - } - - return false; -} - -/** - * refcount_sub_and_test - subtract from a refcount and test if it is 0 - * @i: amount to subtract from the refcount - * @r: the refcount - * - * 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 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() - * must come after. - * - * Use of this function is not recommended for the normal reference counting - * use case in which references are taken and released one at a time. In these - * cases, refcount_dec(), or one of its variants, should instead be used to - * decrement a reference count. - * - * Return: true if the resulting refcount is 0, false otherwise - */ -static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r) -{ - return __refcount_sub_and_test(i, r, NULL); -} - -static inline __must_check bool __refcount_dec_and_test(refcount_t *r, int *oldp) -{ - return __refcount_sub_and_test(1, r, oldp); -} - -/** - * refcount_dec_and_test - decrement a refcount and test if it is 0 - * @r: the refcount - * - * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to - * 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() - * must come after. - * - * Return: true if the resulting refcount is 0, false otherwise - */ -static inline __must_check bool refcount_dec_and_test(refcount_t *r) -{ - return __refcount_dec_and_test(r, NULL); -} - -static inline void __refcount_dec(refcount_t *r, int *oldp) -{ - int old = atomic_sub_return_release(1, &r->refs); - - if (oldp) - *oldp = old; -} - -/** - * refcount_dec - decrement a refcount - * @r: the refcount - * - * Similar to atomic_dec(), it will WARN on underflow and fail to decrement - * when saturated at REFCOUNT_SATURATED. - * - * Provides release memory ordering, such that prior loads and stores are done - * before. - */ -static inline void refcount_dec(refcount_t *r) -{ - __refcount_dec(r, NULL); -} - -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) __cond_acquires(lock); -extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) __cond_acquires(lock); -extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r, - spinlock_t *lock, - unsigned long *flags) __cond_acquires(lock); -#endif /* _LINUX_REFCOUNT_H */ |