1 files changed, 217 insertions, 88 deletions

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index a89cf09a8268..6111bcb28376 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -1,6 +1,8 @@
 #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>
 
 /*
@@ -11,8 +13,8 @@
  * 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
@@ -25,75 +27,64 @@
  * 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()
@@ -107,26 +98,39 @@ EXPORT_SYMBOL_GPL(percpu_ref_reinit);
  */
 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
@@ -140,21 +144,137 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
          * 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);
 }
 
 /**
@@ -164,39 +284,48 @@ static void percpu_ref_kill_rcu(struct rcu_head *rcu)
  *
  * 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);