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authorTejun Heo <tj@kernel.org>2015-09-29 17:47:18 -0400
committerTejun Heo <tj@kernel.org>2016-08-10 15:02:58 -0400
commit18808354b79622ed11857e41f9044ba17aec5b01 (patch)
tree44f91394a6c0385b30e5271432ff0300cc17ef83
parentb2302c7fdc654d249c546aac6228b8e10969bc1e (diff)
percpu_ref: unify staggered atomic switching wait behavior
When an atomic or percpu switching starts before the previous atomic switching finishes, the taken behaviors are * If the new atomic switching has confirmation callback, it waits for the previous atomic switching to complete. * If the new percpu switching is the first percpu switching following the previous atomic switching, it waits the previous atomic switching to complete. No percpu_ref user depends on these subtleties. The only meaningful part is that, if the caller ensures that atomic switching isn't in progress, mode switching operations can be issued from any context. This patch pulls the wait logic to the top of both switching functions so that they always wait for the previous atomic switching to complete. This makes the behavior simpler and consistent for both directions and will help allowing concurrent invocations of mode switching functions. Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r--lib/percpu-refcount.c31
1 files changed, 21 insertions, 10 deletions
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 599a78c0633b..c3617a8525d7 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -161,15 +161,19 @@ 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) {
- /*
- * Somebody else already set ATOMIC. Wait for its
- * completion and invoke @confirm_switch() directly.
- */
- wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
+ if (confirm_switch)
confirm_switch(ref);
- }
return;
}
@@ -180,7 +184,6 @@ static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref,
* 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 */
@@ -192,13 +195,21 @@ 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))
return;
- wait_event(percpu_ref_switch_waitq, !ref->confirm_switch);
-
atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);
/*