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percpu-refcount: require percpu_ref to be exited explicitly

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Currently, a percpu_ref undoes percpu_ref_init() automatically by
freeing the allocated percpu area when the percpu_ref is killed.
While seemingly convenient, this has the following niggles.

* It's impossible to re-init a released reference counter without
  going through re-allocation.

* In the similar vein, it's impossible to initialize a percpu_ref
  count with static percpu variables.

* We need and have an explicit destructor anyway for failure paths -
  percpu_ref_cancel_init().

This patch removes the automatic percpu counter freeing in
percpu_ref_kill_rcu() and repurposes percpu_ref_cancel_init() into a
generic destructor now named percpu_ref_exit().  percpu_ref_destroy()
is considered but it gets confusing with percpu_ref_kill() while
"exit" clearly indicates that it's the counterpart of
percpu_ref_init().

All percpu_ref_cancel_init() users are updated to invoke
percpu_ref_exit() instead and explicit percpu_ref_exit() calls are
added to the destruction path of all percpu_ref users.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Cc: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo
2014-06-28 08:10:14 -04:00
parent 7d74207512
commit 9a1049da9b
5 changed files with 24 additions and 33 deletions
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6
fs/aio.c
View File

@@ -506,6 +506,8 @@ static void free_ioctx(struct work_struct *work)
aio_free_ring(ctx);
free_percpu(ctx->cpu);
percpu_ref_exit(&ctx->reqs);
percpu_ref_exit(&ctx->users);
kmem_cache_free(kioctx_cachep, ctx);
}
@@ -715,8 +717,8 @@ err_ctx:
err:
mutex_unlock(&ctx->ring_lock);
free_percpu(ctx->cpu);
percpu_ref_cancel_init(&ctx->reqs);
percpu_ref_cancel_init(&ctx->users);
percpu_ref_exit(&ctx->reqs);
percpu_ref_exit(&ctx->users);
kmem_cache_free(kioctx_cachep, ctx);
pr_debug("error allocating ioctx %d\n", err);
return ERR_PTR(err);