percpu_ref: restructure operation mode switching

Restructure atomic/percpu mode switching.

* The users of __percpu_ref_switch_to_atomic/percpu() now call a new
  function __percpu_ref_switch_mode() which calls either of the
  original switching functions depending on the current state of
  ref->force_atomic and the __PERCPU_REF_DEAD flag.  The callers no
  longer check whether switching is necessary but always invoke
  __percpu_ref_switch_mode().

* !ref->confirm_switch waiting is collected into
  __percpu_ref_switch_mode().

This patch doesn't cause any behavior differences.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 29 insertions, 35 deletions

diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index c3617a8525d7..f3ff793691ac 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -161,16 +161,6 @@ 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 the previous ATOMIC switching hasn't finished yet, wait for
-         * its completion.  If the caller ensures that ATOMIC switching
-         * isn't in progress, this function can be called from any context.
-         * Do an extra confirm_switch test to circumvent the unconditional
-         * might_sleep() in wait_event().
-         */
-        if (ref->confirm_switch)
-                wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
-
         if (ref->percpu_count_ptr & __PERCPU_REF_ATOMIC) {
                 if (confirm_switch)
                         confirm_switch(ref);
@@ -195,16 +185,6 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
         unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
         int cpu;
 
-        /*
-         * If the previous ATOMIC switching hasn't finished yet, wait for
-         * its completion.  If the caller ensures that ATOMIC switching
-         * isn't in progress, this function can be called from any context.
-         * Do an extra confirm_switch test to circumvent the unconditional
-         * might_sleep() in wait_event().
-         */
-        if (ref->confirm_switch)
-                wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
-
         BUG_ON(!percpu_count);
 
         if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
@@ -225,6 +205,25 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
                           ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC);
 }
 
+static void __percpu_ref_switch_mode(struct percpu_ref *ref,
+                                     percpu_ref_func_t *confirm_switch)
+{
+        /*
+         * If the previous ATOMIC switching hasn't finished yet, wait for
+         * its completion.  If the caller ensures that ATOMIC switching
+         * isn't in progress, this function can be called from any context.
+         * Do an extra confirm_switch test to circumvent the unconditional
+         * might_sleep() in wait_event().
+         */
+        if (ref->confirm_switch)
+                wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
+
+        if (ref->force_atomic || (ref->percpu_count_ptr & __PERCPU_REF_DEAD))
+                __percpu_ref_switch_to_atomic(ref, confirm_switch);
+        else
+                __percpu_ref_switch_to_percpu(ref);
+}
+
 /**
  * percpu_ref_switch_to_atomic - switch a percpu_ref to atomic mode
  * @ref: percpu_ref to switch to atomic mode
@@ -241,16 +240,15 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
  * 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.
+ * This function may block if @ref is in the process of switching to atomic
+ * mode.  If the caller ensures that @ref is not in the process of
+ * switching to atomic mode, this function can be called from any context.
  */
 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);
+        __percpu_ref_switch_mode(ref, confirm_switch);
 }
 
 /**
@@ -267,17 +265,14 @@ void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
  * 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().
+ * This function may block if @ref is in the process of switching to atomic
+ * mode.  If the caller ensures that @ref is not in the process of
+ * switching to atomic mode, this function can be called from any context.
  */
 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);
+        __percpu_ref_switch_mode(ref, NULL);
 }
 
 /**
@@ -302,7 +297,7 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
                   "%s called more than once on %pf!", __func__, ref->release);
 
         ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
-        __percpu_ref_switch_to_atomic(ref, confirm_kill);
+        __percpu_ref_switch_mode(ref, confirm_kill);
         percpu_ref_put(ref);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
@@ -324,7 +319,6 @@ void percpu_ref_reinit(struct percpu_ref *ref)
 
         ref->percpu_count_ptr &= ~__PERCPU_REF_DEAD;
         percpu_ref_get(ref);
-        if (!ref->force_atomic)
-                __percpu_ref_switch_to_percpu(ref);
+        __percpu_ref_switch_mode(ref, NULL);
 }
 EXPORT_SYMBOL_GPL(percpu_ref_reinit);