#define pr_fmt(fmt) "%s: " fmt "\n", __func__
#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
#include <linux/percpu-refcount.h>
/*
* percpu counters will all sum to the correct value
*
* (More precisely: because moduler arithmatic is commutative the sum of all the
- * pcpu_count vars will be equal to what it would have been if all the gets and
- * puts were done to a single integer, even if some of the percpu integers
+ * percpu_count vars will be equal to what it would have been if all the gets
+ * and puts were done to a single integer, even if some of the percpu integers
* overflow or underflow).
*
* The real trick to implementing percpu refcounts is shutdown. We can't detect
* works.
*
* Converting to non percpu mode is done with some RCUish stuff in
- * percpu_ref_kill. Additionally, we need a bias value so that the atomic_t
- * can't hit 0 before we've added up all the percpu refs.
+ * percpu_ref_kill. Additionally, we need a bias value so that the
+ * atomic_long_t can't hit 0 before we've added up all the percpu refs.
*/
-#define PCPU_COUNT_BIAS (1U << 31)
+#define PERCPU_COUNT_BIAS (1LU << (BITS_PER_LONG - 1))
-static unsigned __percpu *pcpu_count_ptr(struct percpu_ref *ref)
+static DECLARE_WAIT_QUEUE_HEAD(percpu_ref_switch_waitq);
+
+static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
{
- return (unsigned __percpu *)(ref->pcpu_count_ptr & ~PCPU_REF_DEAD);
+ return (unsigned long __percpu *)
+ (ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
}
/**
* percpu_ref_init - initialize a percpu refcount
* @ref: percpu_ref to initialize
* @release: function which will be called when refcount hits 0
+ * @flags: PERCPU_REF_INIT_* flags
+ * @gfp: allocation mask to use
*
- * Initializes the refcount in single atomic counter mode with a refcount of 1;
- * analagous to atomic_set(ref, 1).
+ * Initializes @ref. If @flags is zero, @ref starts in percpu mode with a
+ * refcount of 1; analagous to atomic_long_set(ref, 1). See the
+ * definitions of PERCPU_REF_INIT_* flags for flag behaviors.
*
* Note that @release must not sleep - it may potentially be called from RCU
* callback context by percpu_ref_kill().
*/
-int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release)
+int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
+ unsigned int flags, gfp_t gfp)
{
- atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS);
+ size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
+ __alignof__(unsigned long));
+ unsigned long start_count = 0;
- ref->pcpu_count_ptr = (unsigned long)alloc_percpu(unsigned);
- if (!ref->pcpu_count_ptr)
+ ref->percpu_count_ptr = (unsigned long)
+ __alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
+ if (!ref->percpu_count_ptr)
return -ENOMEM;
- ref->release = release;
- return 0;
-}
-EXPORT_SYMBOL_GPL(percpu_ref_init);
-
-/**
- * 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)
-{
- unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
- int cpu;
+ ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
- BUG_ON(!pcpu_count);
- WARN_ON(!percpu_ref_is_zero(ref));
+ if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
+ ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
+ else
+ start_count += PERCPU_COUNT_BIAS;
- atomic_set(&ref->count, 1 + PCPU_COUNT_BIAS);
+ if (flags & PERCPU_REF_INIT_DEAD)
+ ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
+ else
+ start_count++;
- /*
- * Restore per-cpu operation. smp_store_release() is paired with
- * smp_read_barrier_depends() in __pcpu_ref_alive() and guarantees
- * that the zeroing is visible to all percpu accesses which can see
- * the following PCPU_REF_DEAD clearing.
- */
- for_each_possible_cpu(cpu)
- *per_cpu_ptr(pcpu_count, cpu) = 0;
+ atomic_long_set(&ref->count, start_count);
- smp_store_release(&ref->pcpu_count_ptr,
- ref->pcpu_count_ptr & ~PCPU_REF_DEAD);
+ ref->release = release;
+ return 0;
}
-EXPORT_SYMBOL_GPL(percpu_ref_reinit);
+EXPORT_SYMBOL_GPL(percpu_ref_init);
/**
* percpu_ref_exit - undo percpu_ref_init()
*/
void percpu_ref_exit(struct percpu_ref *ref)
{
- unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
+ unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
- if (pcpu_count) {
- free_percpu(pcpu_count);
- ref->pcpu_count_ptr = PCPU_REF_DEAD;
+ if (percpu_count) {
+ free_percpu(percpu_count);
+ ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
}
}
EXPORT_SYMBOL_GPL(percpu_ref_exit);
-static void percpu_ref_kill_rcu(struct rcu_head *rcu)
+static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
+{
+ struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
+
+ ref->confirm_switch(ref);
+ ref->confirm_switch = NULL;
+ wake_up_all(&percpu_ref_switch_waitq);
+
+ /* drop ref from percpu_ref_switch_to_atomic() */
+ percpu_ref_put(ref);
+}
+
+static void percpu_ref_switch_to_atomic_rcu(struct rcu_head *rcu)
{
struct percpu_ref *ref = container_of(rcu, struct percpu_ref, rcu);
- unsigned __percpu *pcpu_count = pcpu_count_ptr(ref);
- unsigned count = 0;
+ unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
+ unsigned long count = 0;
int cpu;
for_each_possible_cpu(cpu)
- count += *per_cpu_ptr(pcpu_count, cpu);
+ count += *per_cpu_ptr(percpu_count, cpu);
- pr_debug("global %i pcpu %i", atomic_read(&ref->count), (int) count);
+ pr_debug("global %ld percpu %ld",
+ atomic_long_read(&ref->count), (long)count);
/*
* It's crucial that we sum the percpu counters _before_ adding the sum
* reaching 0 before we add the percpu counts. But doing it at the same
* time is equivalent and saves us atomic operations:
*/
+ atomic_long_add((long)count - PERCPU_COUNT_BIAS, &ref->count);
+
+ WARN_ONCE(atomic_long_read(&ref->count) <= 0,
+ "percpu ref (%pf) <= 0 (%ld) after switching to atomic",
+ ref->release, atomic_long_read(&ref->count));
+
+ /* @ref is viewed as dead on all CPUs, send out switch confirmation */
+ percpu_ref_call_confirm_rcu(rcu);
+}
+
+static void percpu_ref_noop_confirm_switch(struct percpu_ref *ref)
+{
+}
+
+static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
+ percpu_ref_func_t *confirm_switch)
+{
+ if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC)) {
+ /* switching from percpu to atomic */
+ ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
+
+ /*
+ * Non-NULL ->confirm_switch is used to indicate that
+ * switching is in progress. Use noop one if unspecified.
+ */
+ WARN_ON_ONCE(ref->confirm_switch);
+ ref->confirm_switch =
+ confirm_switch ?: percpu_ref_noop_confirm_switch;
+
+ percpu_ref_get(ref); /* put after confirmation */
+ call_rcu_sched(&ref->rcu, percpu_ref_switch_to_atomic_rcu);
+ } else if (confirm_switch) {
+ /*
+ * Somebody already set ATOMIC. Switching may still be in
+ * progress. @confirm_switch must be invoked after the
+ * switching is complete and a full sched RCU grace period
+ * has passed. Wait synchronously for the previous
+ * switching and schedule @confirm_switch invocation.
+ */
+ wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
+ ref->confirm_switch = confirm_switch;
- atomic_add((int) count - PCPU_COUNT_BIAS, &ref->count);
+ percpu_ref_get(ref); /* put after confirmation */
+ call_rcu_sched(&ref->rcu, percpu_ref_call_confirm_rcu);
+ }
+}
+
+/**
+ * percpu_ref_switch_to_atomic - switch a percpu_ref to atomic mode
+ * @ref: percpu_ref to switch to atomic mode
+ * @confirm_switch: optional confirmation callback
+ *
+ * There's no reason to use this function for the usual reference counting.
+ * Use percpu_ref_kill[_and_confirm]().
+ *
+ * Schedule switching of @ref to atomic mode. All its percpu counts will
+ * be collected to the main atomic counter. On completion, when all CPUs
+ * are guaraneed to be in atomic mode, @confirm_switch, which may not
+ * block, is invoked. This function may be invoked concurrently with all
+ * the get/put operations and can safely be mixed with kill and reinit
+ * operations. Note that @ref will stay in atomic mode across kill/reinit
+ * cycles until percpu_ref_switch_to_percpu() is called.
+ *
+ * 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. In such cases, @confirm_switch
+ * will be invoked after the switching is complete.
+ *
+ * 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
+ * implementation detail and must not be depended upon.
+ */
+void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
+ percpu_ref_func_t *confirm_switch)
+{
+ ref->force_atomic = true;
+ __percpu_ref_switch_to_atomic(ref, confirm_switch);
+}
- WARN_ONCE(atomic_read(&ref->count) <= 0, "percpu ref <= 0 (%i)",
- atomic_read(&ref->count));
+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);
- /* @ref is viewed as dead on all CPUs, send out kill confirmation */
- if (ref->confirm_kill)
- ref->confirm_kill(ref);
+ 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);
/*
- * Now we're in single atomic_t mode with a consistent refcount, so it's
- * safe to drop our initial ref:
+ * 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 clearing.
*/
- percpu_ref_put(ref);
+ 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);
+}
+
+/**
+ * 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 reverses the sticky atomic state set
+ * by PERCPU_REF_INIT_ATOMIC or percpu_ref_switch_to_atomic(). If @ref is
+ * dying or dead, the actual switching takes place on the following
+ * percpu_ref_reinit().
+ *
+ * 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)
+{
+ ref->force_atomic = false;
+
+ /* 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);
}
/**
*
* Equivalent to percpu_ref_kill() but also schedules kill confirmation if
* @confirm_kill is not NULL. @confirm_kill, which may not block, will be
- * called after @ref is seen as dead from all CPUs - all further
- * invocations of percpu_ref_tryget() will fail. See percpu_ref_tryget()
- * for more details.
+ * called after @ref is seen as dead from all CPUs at which point all
+ * further invocations of percpu_ref_tryget_live() will fail. See
+ * 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 in the
+ * process of switching to atomic mode by percpu_ref_switch_atomic().
*
- * Due to the way percpu_ref is implemented, @confirm_kill will be called
- * after at least one full RCU grace period has passed but this is an
- * implementation detail and callers must not depend on it.
+ * 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
+ * implementation detail and must not be depended upon.
*/
void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
percpu_ref_func_t *confirm_kill)
{
- WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,
- "percpu_ref_kill() called more than once!\n");
+ WARN_ONCE(ref->percpu_count_ptr & __PERCPU_REF_DEAD,
+ "%s called more than once on %pf!", __func__, ref->release);
- ref->pcpu_count_ptr |= PCPU_REF_DEAD;
- ref->confirm_kill = confirm_kill;
-
- call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
+ ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
+ __percpu_ref_switch_to_atomic(ref, confirm_kill);
+ percpu_ref_put(ref);
}
EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
-/*
- * XXX: Temporary kludge to work around SCSI blk-mq stall. Used only by
- * block/blk-mq.c::blk_mq_freeze_queue(). Will be removed during v3.18
- * devel cycle. Do not use anywhere else.
+/**
+ * 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() ignoring %PERCPU_REF_INIT_DEAD. @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_kill_expedited(struct percpu_ref *ref)
+void percpu_ref_reinit(struct percpu_ref *ref)
{
- WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,
- "percpu_ref_kill() called more than once on %pf!",
- ref->release);
+ WARN_ON_ONCE(!percpu_ref_is_zero(ref));
- ref->pcpu_count_ptr |= PCPU_REF_DEAD;
- synchronize_sched_expedited();
- percpu_ref_kill_rcu(&ref->rcu);
+ ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;
+ percpu_ref_get(ref);
+ if (!ref->force_atomic)
+ __percpu_ref_switch_to_percpu(ref);
}
+EXPORT_SYMBOL_GPL(percpu_ref_reinit);
projects / firefly-linux-kernel-4.4.55.git / blobdiff