Commit a67823c1 authored by Roman Pen's avatar Roman Pen Committed by Tejun Heo

percpu-refcount: init ->confirm_switch member properly

This patch targets two things which are related to ->confirm_switch:

 1. Init ->confirm_switch pointer with NULL on percpu_ref_init() or
    kernel frightfully complains with WARN_ON_ONCE(ref->confirm_switch)
    at __percpu_ref_switch_to_atomic if memory chunk was not properly
    zeroed.

 2. Warn if RCU callback is still in progress on percpu_ref_exit().
    The race still exists, because percpu_ref_call_confirm_rcu()
    drops ->confirm_switch to NULL early, but that is only a warning
    and still the caller is responsible that ref is no longer in
    active use.  Hopefully that can help to catch incorrect usage
    of percpu-refcount.
Signed-off-by: default avatarRoman Pen <roman.penyaev@profitbricks.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 33e465ce
...@@ -83,6 +83,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release, ...@@ -83,6 +83,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
atomic_long_set(&ref->count, start_count); atomic_long_set(&ref->count, start_count);
ref->release = release; ref->release = release;
ref->confirm_switch = NULL;
return 0; return 0;
} }
EXPORT_SYMBOL_GPL(percpu_ref_init); EXPORT_SYMBOL_GPL(percpu_ref_init);
...@@ -102,6 +103,8 @@ void percpu_ref_exit(struct percpu_ref *ref) ...@@ -102,6 +103,8 @@ void percpu_ref_exit(struct percpu_ref *ref)
unsigned long __percpu *percpu_count = percpu_count_ptr(ref); unsigned long __percpu *percpu_count = percpu_count_ptr(ref);
if (percpu_count) { if (percpu_count) {
/* non-NULL confirm_switch indicates switching in progress */
WARN_ON_ONCE(ref->confirm_switch);
free_percpu(percpu_count); free_percpu(percpu_count);
ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD; ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD;
} }
......
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