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Groups > linux.kernel > #1522639
| From | Boqun Feng <boqun.feng@gmail.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCH 7/7] kref: Implement using refcount_t |
| Date | 2016-11-15 13:40 +0100 |
| Message-ID | <sDLbQ-4VX-3@gated-at.bofh.it> (permalink) |
| References | <sDtyh-1DM-5@gated-at.bofh.it> <sDtyi-1DM-23@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
[Multipart message — attachments visible in raw view] - view raw
Hi Peter,
On Mon, Nov 14, 2016 at 06:39:53PM +0100, Peter Zijlstra wrote:
[...]
> +/*
> + * 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.
I'm not sure this is correct, the RELEASE semantics is for the STORE
part of cmpxchg, and semantically it will guarantee that memory
operations after cmpxchg won't be reordered upwards, for example, on
ARM64, the following code:
WRITE_ONCE(x, 1)
atomic_cmpxchg_release(&a, 1, 2);
r1 = ll(&a)
if (r1 == 1) {
sc_release(&a, 2);
}
free()
could be reordered as, I think:
atomic_cmpxchg_release(&a, 1, 2);
r1 = ll(&a)
if (r1 == 1) {
free()
WRITE_ONCE(x, 1)
sc_release(&a, 2);
}
Of course, we need to wait for Will to confirm about this. But if this
could happen, we'd better to use a smp_mb()+atomic_cmpxchg_relaxed()
here and for other refcount_dec_and_*().
That said, I think the really ordering guarantee we need here is that
two cmpxchg()s in refcount_dec_and_*() could be paired with each other
to ensure nobody observes a freed object inside a refcount critical
section. In that case, we need atomic_cmpxchg() here for ordering on
both sides. Or maybe replace atomic_read() with smp_load_acquire().
Regards,
Boqun
> + */
> +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 */
>
>
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[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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