[PATCH 1/3] kref refcnt and false positives

Greg KH
2006-12-20T20:04:30Z

From: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>

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>
---
lib/kref.c | 7 +------
1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/lib/kref.c b/lib/kref.c
index 4a467fa..0d07cc3 100644
--- a/lib/kref.c
+++ b/lib/kref.c
@@ -52,12 +52,7 @@ int kref_put(struct kref *kref, void (*release)(struct kref *kref))
WARN_ON(release == NULL);
WARN_ON(release == (void (*)(struct kref *))kfree);

- /*
- * if current count is one, we are the last user and can release object
- * right now, avoiding an atomic operation on 'refcount'
- */
- if ((atomic_read(&kref->refcount) == 1) ||
- (atomic_dec_and_test(&kref->refcount))) {
+ if (atomic_dec_and_test(&kref->refcount)) {
release(kref);
return 1;
}
--
1.4.4.2