From f334b60b43a0927f4ab1187cbdb4582f5227c3b1 Mon Sep 17 00:00:00 2001 From: Venkatesh Pallipadi Date: Tue, 19 Dec 2006 13:01:29 -0800 Subject: 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: [] dump_trace+0xaa/0x3ef [] show_trace+0x3a/0x50 [] dump_stack+0x15/0x17 [] kobject_init+0x3f/0x8a [] kobject_register+0x1a/0x3e [] sysdev_register+0x5b/0xf9 [] mce_create_device+0x77/0xf4 [] mce_cpu_callback+0x3a/0xe5 [] notifier_call_chain+0x26/0x3b [] raw_notifier_call_chain+0x9/0xb [] _cpu_up+0xb4/0xdc [] cpu_up+0x2b/0x42 [] store_online+0x4a/0x72 [] sysdev_store+0x24/0x26 [] sysfs_write_file+0xcf/0xfc [] vfs_write+0xae/0x154 [] sys_write+0x47/0x6f [] 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 Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- lib/kref.c | 7 +------ 1 file changed, 1 insertion(+), 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; } -- cgit v1.1