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percpu-refcount: init ->confirm_switch member properly

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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: Roman Pen <roman.penyaev@profitbricks.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Roman Pen 2016-08-11 19:27:09 +02:00 committed by Tejun Heo
parent 33e465ce7c
commit a67823c1ed
1 changed files with 3 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

3
lib/percpu-refcount.c
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@ -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)
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;
} }