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author | Linus Torvalds <torvalds@linux-foundation.org> | 2015-02-10 02:55:45 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-02-10 02:55:45 (GMT) |
commit | c2189e3a3d67e94941c568ee8fab1b86983cd024 (patch) | |
tree | 57622099fc953f33309c8059050cb3e0517c2ebc /include | |
parent | ed824a625006e47d2584ee0bba9227a34cc06671 (diff) | |
parent | 4c907baf36d8339f393bb576d0bab29194d0e6ad (diff) | |
download | linux-c2189e3a3d67e94941c568ee8fab1b86983cd024.tar.xz |
Merge branch 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu
Pull percpu changes from Tejun Heo:
"Nothing too interesting. One cleanup patch and another to add a
trivial state check function"
* 'for-3.20' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu:
percpu_ref: implement percpu_ref_is_dying()
percpu_ref: remove unnecessary ACCESS_ONCE() in percpu_ref_tryget_live()
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/percpu-refcount.h | 34 |
1 files changed, 31 insertions, 3 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h index b433764..12c9b48 100644 --- a/include/linux/percpu-refcount.h +++ b/include/linux/percpu-refcount.h @@ -128,8 +128,22 @@ static inline void percpu_ref_kill(struct percpu_ref *ref) static inline bool __ref_is_percpu(struct percpu_ref *ref, unsigned long __percpu **percpu_countp) { - /* paired with smp_store_release() in percpu_ref_reinit() */ - unsigned long percpu_ptr = lockless_dereference(ref->percpu_count_ptr); + unsigned long percpu_ptr; + + /* + * The value of @ref->percpu_count_ptr is tested for + * !__PERCPU_REF_ATOMIC, which may be set asynchronously, and then + * used as a pointer. If the compiler generates a separate fetch + * when using it as a pointer, __PERCPU_REF_ATOMIC may be set in + * between contaminating the pointer value, meaning that + * ACCESS_ONCE() is required when fetching it. + * + * Also, we need a data dependency barrier to be paired with + * smp_store_release() in __percpu_ref_switch_to_percpu(). + * + * Use lockless deref which contains both. + */ + percpu_ptr = lockless_dereference(ref->percpu_count_ptr); /* * Theoretically, the following could test just ATOMIC; however, @@ -233,7 +247,7 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref) if (__ref_is_percpu(ref, &percpu_count)) { this_cpu_inc(*percpu_count); ret = true; - } else if (!(ACCESS_ONCE(ref->percpu_count_ptr) & __PERCPU_REF_DEAD)) { + } else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) { ret = atomic_long_inc_not_zero(&ref->count); } @@ -281,6 +295,20 @@ static inline void percpu_ref_put(struct percpu_ref *ref) } /** + * percpu_ref_is_dying - test whether a percpu refcount is dying or dead + * @ref: percpu_ref to test + * + * Returns %true if @ref is dying or dead. + * + * This function is safe to call as long as @ref is between init and exit + * and the caller is responsible for synchronizing against state changes. + */ +static inline bool percpu_ref_is_dying(struct percpu_ref *ref) +{ + return ref->percpu_count_ptr & __PERCPU_REF_DEAD; +} + +/** * percpu_ref_is_zero - test whether a percpu refcount reached zero * @ref: percpu_ref to test * |