8b5536bbee
Avoid an atomic operation in kref_put() when the last reference is dropped. On most platforms, atomic_read() is a plan read of the counter and involves no atomic at all. Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
/*
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* kref.c - library routines for handling generic reference counted objects
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*
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* Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
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* Copyright (C) 2004 IBM Corp.
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*
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* based on lib/kobject.c which was:
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* Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
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*
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* This file is released under the GPLv2.
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*
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*/
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#include <linux/kref.h>
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#include <linux/module.h>
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/**
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* kref_init - initialize object.
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* @kref: object in question.
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*/
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void kref_init(struct kref *kref)
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{
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atomic_set(&kref->refcount,1);
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}
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/**
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* kref_get - increment refcount for object.
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* @kref: object.
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*/
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void kref_get(struct kref *kref)
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{
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WARN_ON(!atomic_read(&kref->refcount));
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atomic_inc(&kref->refcount);
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}
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/**
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* kref_put - decrement refcount for object.
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* @kref: object.
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* @release: pointer to the function that will clean up the object when the
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* last reference to the object is released.
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* This pointer is required, and it is not acceptable to pass kfree
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* in as this function.
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*
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* Decrement the refcount, and if 0, call release().
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* Return 1 if the object was removed, otherwise return 0. Beware, if this
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* function returns 0, you still can not count on the kref from remaining in
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* memory. Only use the return value if you want to see if the kref is now
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* gone, not present.
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*/
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int kref_put(struct kref *kref, void (*release)(struct kref *kref))
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{
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WARN_ON(release == NULL);
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WARN_ON(release == (void (*)(struct kref *))kfree);
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/*
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* if current count is one, we are the last user and can release object
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* right now, avoiding an atomic operation on 'refcount'
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*/
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if ((atomic_read(&kref->refcount) == 1) ||
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(atomic_dec_and_test(&kref->refcount))) {
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release(kref);
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return 1;
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}
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return 0;
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}
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EXPORT_SYMBOL(kref_init);
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EXPORT_SYMBOL(kref_get);
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EXPORT_SYMBOL(kref_put);
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