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author | Tejun Heo <tj@kernel.org> | 2014-09-24 13:31:49 -0400 |
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committer | Tejun Heo <tj@kernel.org> | 2014-09-24 13:31:49 -0400 |
commit | f47ad45784611297b699f3dffb6c7222b76afe64 (patch) | |
tree | 9497c0a4bad4c6b97cfd08bf22a8b2313606ce6a /lib | |
parent | 490c79a65708873228cf114cf00e32c204e4e907 (diff) | |
download | lwn-f47ad45784611297b699f3dffb6c7222b76afe64.tar.gz lwn-f47ad45784611297b699f3dffb6c7222b76afe64.zip |
percpu_ref: decouple switching to percpu mode and reinit
percpu_ref has treated the dropping of the base reference and
switching to atomic mode as an integral operation; however, there's
nothing inherent tying the two together.
The use cases for percpu_ref have been expanding continuously. While
the current init/kill/reinit/exit model can cover a lot, the coupling
of kill/reinit with atomic/percpu mode switching is turning out to be
too restrictive for use cases where many percpu_refs are created and
destroyed back-to-back with only some of them reaching extended
operation. The coupling also makes implementing always-atomic debug
mode difficult.
This patch separates out percpu mode switching into
percpu_ref_switch_to_percpu() and reimplements percpu_ref_reinit() on
top of it.
* DEAD still requires ATOMIC. A dead ref can't be switched to percpu
mode w/o going through reinit.
v2: __percpu_ref_switch_to_percpu() was missing static. Fixed.
Reported by Fengguang aka kbuild test robot.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: kbuild test robot <fengguang.wu@intel.com>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/percpu-refcount.c | 73 |
1 files changed, 54 insertions, 19 deletions
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index 6e0d14366c5d..5a6d43baccc5 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -206,40 +206,54 @@ void percpu_ref_switch_to_atomic(struct percpu_ref *ref, __percpu_ref_switch_to_atomic(ref, confirm_switch); } -/** - * percpu_ref_reinit - re-initialize a percpu refcount - * @ref: perpcu_ref to re-initialize - * - * Re-initialize @ref so that it's in the same state as when it finished - * percpu_ref_init(). @ref must have been initialized successfully, killed - * and reached 0 but not exited. - * - * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while - * this function is in progress. - */ -void percpu_ref_reinit(struct percpu_ref *ref) +static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref) { unsigned long __percpu *percpu_count = percpu_count_ptr(ref); int cpu; BUG_ON(!percpu_count); - WARN_ON_ONCE(!percpu_ref_is_zero(ref)); - atomic_long_set(&ref->count, 1 + PERCPU_COUNT_BIAS); + if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC)) + return; + + wait_event(percpu_ref_switch_waitq, !ref->confirm_switch); + + atomic_long_add(PERCPU_COUNT_BIAS, &ref->count); /* * Restore per-cpu operation. smp_store_release() is paired with * smp_read_barrier_depends() in __ref_is_percpu() and guarantees * that the zeroing is visible to all percpu accesses which can see - * the following __PERCPU_REF_ATOMIC_DEAD clearing. + * the following __PERCPU_REF_ATOMIC clearing. */ for_each_possible_cpu(cpu) *per_cpu_ptr(percpu_count, cpu) = 0; smp_store_release(&ref->percpu_count_ptr, - ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD); + ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC); +} + +/** + * percpu_ref_switch_to_percpu - switch a percpu_ref to percpu mode + * @ref: percpu_ref to switch to percpu mode + * + * There's no reason to use this function for the usual reference counting. + * To re-use an expired ref, use percpu_ref_reinit(). + * + * Switch @ref to percpu mode. This function may be invoked concurrently + * with all the get/put operations and can safely be mixed with kill and + * reinit operations. + * + * This function normally doesn't block and can be called from any context + * but it may block if @ref is in the process of switching to atomic mode + * by percpu_ref_switch_atomic(). + */ +void percpu_ref_switch_to_percpu(struct percpu_ref *ref) +{ + /* a dying or dead ref can't be switched to percpu mode w/o reinit */ + if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) + __percpu_ref_switch_to_percpu(ref); } -EXPORT_SYMBOL_GPL(percpu_ref_reinit); /** * percpu_ref_kill_and_confirm - drop the initial ref and schedule confirmation @@ -253,8 +267,8 @@ EXPORT_SYMBOL_GPL(percpu_ref_reinit); * percpu_ref_tryget_live() for details. * * This function normally doesn't block and can be called from any context - * but it may block if @confirm_kill is specified and @ref is already in - * the process of switching to atomic mode by percpu_ref_switch_atomic(). + * but it may block if @confirm_kill is specified and @ref is in the + * process of switching to atomic mode by percpu_ref_switch_atomic(). * * Due to the way percpu_ref is implemented, @confirm_switch will be called * after at least one full sched RCU grace period has passed but this is an @@ -271,3 +285,24 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref, percpu_ref_put(ref); } EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm); + +/** + * percpu_ref_reinit - re-initialize a percpu refcount + * @ref: perpcu_ref to re-initialize + * + * Re-initialize @ref so that it's in the same state as when it finished + * percpu_ref_init(). @ref must have been initialized successfully and + * reached 0 but not exited. + * + * Note that percpu_ref_tryget[_live]() are safe to perform on @ref while + * this function is in progress. + */ +void percpu_ref_reinit(struct percpu_ref *ref) +{ + WARN_ON_ONCE(!percpu_ref_is_zero(ref)); + + ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD; + percpu_ref_get(ref); + __percpu_ref_switch_to_percpu(ref); +} +EXPORT_SYMBOL_GPL(percpu_ref_reinit); |