kernel-ark/lib/kref.c

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/*
* kref.c - library routines for handling generic reference counted objects
*
* Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
* Copyright (C) 2004 IBM Corp.
*
* based on lib/kobject.c which was:
* Copyright (C) 2002-2003 Patrick Mochel <mochel@osdl.org>
*
* This file is released under the GPLv2.
*
*/
#include <linux/kref.h>
#include <linux/module.h>
/**
* kref_init - initialize object.
* @kref: object in question.
*/
void kref_init(struct kref *kref)
{
atomic_set(&kref->refcount,1);
smp_mb();
}
/**
* kref_get - increment refcount for object.
* @kref: object.
*/
void kref_get(struct kref *kref)
{
WARN_ON(!atomic_read(&kref->refcount));
atomic_inc(&kref->refcount);
smp_mb__after_atomic_inc();
}
/**
* kref_put - decrement refcount for object.
* @kref: object.
* @release: pointer to the function that will clean up the object when the
* last reference to the object is released.
* This pointer is required, and it is not acceptable to pass kfree
* in as this function.
*
* Decrement the refcount, and if 0, call release().
* Return 1 if the object was removed, otherwise return 0. Beware, if this
* function returns 0, you still can not count on the kref from remaining in
* memory. Only use the return value if you want to see if the kref is now
* gone, not present.
*/
int kref_put(struct kref *kref, void (*release)(struct kref *kref))
{
WARN_ON(release == NULL);
WARN_ON(release == (void (*)(struct kref *))kfree);
kref refcnt and false positives With WARN_ON addition to kobject_init() [ http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.19/2.6.19-mm1/dont-use/broken-out/gregkh-driver-kobject-warn.patch ] I started seeing following WARNING on CPU offline followed by online on my x86_64 system. WARNING at lib/kobject.c:172 kobject_init() Call Trace: [<ffffffff8020ab45>] dump_trace+0xaa/0x3ef [<ffffffff8020aec4>] show_trace+0x3a/0x50 [<ffffffff8020b0f6>] dump_stack+0x15/0x17 [<ffffffff80350abc>] kobject_init+0x3f/0x8a [<ffffffff80350be1>] kobject_register+0x1a/0x3e [<ffffffff803bbd89>] sysdev_register+0x5b/0xf9 [<ffffffff80211d0b>] mce_create_device+0x77/0xf4 [<ffffffff80211dc2>] mce_cpu_callback+0x3a/0xe5 [<ffffffff805632fd>] notifier_call_chain+0x26/0x3b [<ffffffff8023f6f3>] raw_notifier_call_chain+0x9/0xb [<ffffffff802519bf>] _cpu_up+0xb4/0xdc [<ffffffff80251a12>] cpu_up+0x2b/0x42 [<ffffffff803bef00>] store_online+0x4a/0x72 [<ffffffff803bb6ce>] sysdev_store+0x24/0x26 [<ffffffff802baaa2>] sysfs_write_file+0xcf/0xfc [<ffffffff8027fc6f>] vfs_write+0xae/0x154 [<ffffffff80280418>] sys_write+0x47/0x6f [<ffffffff8020963e>] system_call+0x7e/0x83 DWARF2 unwinder stuck at system_call+0x7e/0x83 Leftover inexact backtrace: This is a false positive as mce.c is unregistering/registering sysfs interfaces cleanly on hotplug. kref_put() and conditional decrement of refcnt seems to be the root cause for this and the patch below resolves the issue for me. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2006-12-19 21:01:29 +00:00
if (atomic_dec_and_test(&kref->refcount)) {
release(kref);
return 1;
}
return 0;
}
EXPORT_SYMBOL(kref_init);
EXPORT_SYMBOL(kref_get);
EXPORT_SYMBOL(kref_put);