Re: kref refcnt and false positives

From: David Woodhouse
Date: Sun Dec 31 2006 - 10:16:43 EST

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On Thu, 2006-12-21 at 09:01 +0000, Linux Kernel Mailing List wrote:
> Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=f334b60b43a0927f4ab1187cbdb4582f5227c3b1
> Commit: f334b60b43a0927f4ab1187cbdb4582f5227c3b1
> Parent: f238085415c56618e042252894f2fcc971add645
> Author: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
> AuthorDate: Tue Dec 19 13:01:29 2006 -0800
> Committer: Greg Kroah-Hartman <gregkh@xxxxxxx>
> CommitDate: Wed Dec 20 10:56:43 2006 -0800
>
> 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()
>
<...>
> 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@xxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> ---
> 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;
> }

This makes my Maple board very unhappy -- it triggers a WARN_ON() in
kref_get() lots of times...

time_init: decrementer frequency = 175.000000 MHz
time_init: processor frequency = 1400.000000 MHz
------------[ cut here ]------------
Badness at lib/kref.c:32
Call Trace:
[C00000000050F440] [C00000000000F4C8] .show_stack+0x68/0x1b0 (unreliable)
[C00000000050F4E0] [C000000000189708] .report_bug+0x94/0xe8
[C00000000050F570] [C000000000021A98] .program_check_exception+0x18c/0x5d0
[C00000000050F640] [C000000000004774] program_check_common+0xf4/0x100
--- Exception: 700 at .kref_get+0xc/0x24
LR = .of_node_get+0x20/0x3c
[C00000000050F930] [C00000000050F9D0] init_thread_union+0x39d0/0x4000 (unreliabl
e)
[C00000000050F9B0] [C000000000020F1C] .of_get_parent+0x38/0x64
[C00000000050FA40] [C00000000001B750] .of_translate_address+0xf0/0x38c
[C00000000050FB50] [C00000000001BA28] .__of_address_to_resource+0x3c/0xe0
[C00000000050FBF0] [C00000000001BB14] .of_address_to_resource+0x48/0x68
[C00000000050FC90] [C00000000045D240] .maple_get_boot_time+0x40/0x12c
[C00000000050FD70] [C00000000001F884] .get_boot_time+0x3c/0xb8
[C00000000050FE10] [C000000000454040] .time_init+0x274/0x450
[C00000000050FEF0] [C00000000044B74C] .start_kernel+0x188/0x2bc
[C00000000050FF90] [C0000000000084C8] .start_here_common+0x54/0x8c
Maple: Found RTC at IO 0x900
Console: colour dummy device 80x25
Dentry cache hash table entries: 65536 (order: 7, 524288 bytes)
Inode-cache hash table entries: 32768 (order: 6, 262144 bytes)
Memory: 501628k/524288k available (4608k kernel code, 21932k reserved, 552k data
, 354k bss, 212k init)
Calibrating delay loop... 349.18 BogoMIPS (lpj=698368)
Mount-cache hash table entries: 256
------------[ cut here ]------------
Badness at lib/kref.c:32
Call Trace:
[C00000000050F7F0] [C00000000000F4C8] .show_stack+0x68/0x1b0 (unreliable)
[C00000000050F890] [C000000000189708] .report_bug+0x94/0xe8
[C00000000050F920] [C000000000021A98] .program_check_exception+0x18c/0x5d0
[C00000000050F9F0] [C000000000004774] program_check_common+0xf4/0x100
--- Exception: 700 at .kref_get+0xc/0x24
LR = .of_node_get+0x20/0x3c
[C00000000050FCE0] [C00000001F7DDF38] 0xc00000001f7ddf38 (unreliable)
[C00000000050FD60] [C000000000020650] .of_find_node_by_path+0x60/0xac
[C00000000050FDE0] [C0000000000EE038] .proc_device_tree_init+0x58/0xa4
[C00000000050FE70] [C0000000004641AC] .proc_root_init+0x134/0x168
[C00000000050FEF0] [C00000000044B860] .start_kernel+0x29c/0x2bc
[C00000000050FF90] [C0000000000084C8] .start_here_common+0x54/0x8c
mpic: requesting IPIs ...
Processor 1 is stuck.
Brought up 1 CPUs
NET: Registered protocol family 16
PCI: Probing PCI hardware
Failed to request PCI IO region on PCI domain 0000
------------[ cut here ]------------
Badness at lib/kref.c:32
Call Trace:
[C00000001F7832E0] [C00000000000F4C8] .show_stack+0x68/0x1b0 (unreliable)
[C00000001F783380] [C000000000189708] .report_bug+0x94/0xe8
[C00000001F783410] [C000000000021A98] .program_check_exception+0x18c/0x5d0
[C00000001F7834E0] [C000000000004774] program_check_common+0xf4/0x100
--- Exception: 700 at .kref_get+0xc/0x24
LR = .of_node_get+0x20/0x3c
[C00000001F7837D0] [C00000001F783870] 0xc00000001f783870 (unreliable)
[C00000001F783850] [C000000000020F1C] .of_get_parent+0x38/0x64
[C00000001F7838E0] [C00000000001ACE4] .of_irq_map_raw+0x100/0x4cc
[C00000001F7839E0] [C00000000001B190] .of_irq_map_one+0xe0/0x11c
[C00000001F783A90] [C00000000001BFB4] .of_irq_map_pci+0x74/0x1b8
[C00000001F783B40] [C0000000000271EC] .pci_read_irq_line+0x20/0x100
[C00000001F783BF0] [C00000000002741C] .do_bus_setup+0x94/0x108
[C00000001F783C80] [C000000000027538] .pcibios_fixup_bus+0xa8/0x11c
[C00000001F783D00] [C000000000196620] .pci_scan_child_bus+0x64/0x100
[C00000001F783DA0] [C000000000028388] .scan_phb+0x1a0/0x1d8
[C00000001F783E40] [C00000000045A190] .pcibios_init+0x4c/0x18c
[C00000001F783EC0] [C0000000000093AC] .init+0x1bc/0x394
[C00000001F783F90] [C000000000023364] .kernel_thread+0x4c/0x68
------------[ cut here ]------------
Badness at lib/kref.c:32
Call Trace:
[C00000001F7832E0] [C00000000000F4C8] .show_stack+0x68/0x1b0 (unreliable)
[C00000001F783380] [C000000000189708] .report_bug+0x94/0xe8
[C00000001F783410] [C000000000021A98] .program_check_exception+0x18c/0x5d0
[C00000001F7834E0] [C000000000004774] program_check_common+0xf4/0x100
--- Exception: 700 at .kref_get+0xc/0x24
LR = .of_node_get+0x20/0x3c
[C00000001F7837D0] [C00000001F783870] 0xc00000001f783870 (unreliable)
[C00000001F783850] [C000000000020F1C] .of_get_parent+0x38/0x64
[C00000001F7838E0] [C00000000001ACE4] .of_irq_map_raw+0x100/0x4cc
[C00000001F7839E0] [C00000000001B190] .of_irq_map_one+0xe0/0x11c
[C00000001F783A90] [C00000000001BFB4] .of_irq_map_pci+0x74/0x1b8
[C00000001F783B40] [C0000000000271EC] .pci_read_irq_line+0x20/0x100
[C00000001F783BF0] [C00000000002741C] .do_bus_setup+0x94/0x108
[C00000001F783C80] [C000000000027538] .pcibios_fixup_bus+0xa8/0x11c
[C00000001F783D00] [C000000000196620] .pci_scan_child_bus+0x64/0x100
[C00000001F783DA0] [C000000000028388] .scan_phb+0x1a0/0x1d8
[C00000001F783E40] [C00000000045A190] .pcibios_init+0x4c/0x18c
[C00000001F783EC0] [C0000000000093AC] .init+0x1bc/0x394
[C00000001F783F90] [C000000000023364] .kernel_thread+0x4c/0x68
------------[ cut here ]------------
Badness at lib/kref.c:32
Call Trace:
[C00000001F7832E0] [C00000000000F4C8] .show_stack+0x68/0x1b0 (unreliable)
[C00000001F783380] [C000000000189708] .report_bug+0x94/0xe8
[C00000001F783410] [C000000000021A98] .program_check_exception+0x18c/0x5d0
[C00000001F7834E0] [C000000000004774] program_check_common+0xf4/0x100
--- Exception: 700 at .kref_get+0xc/0x24
LR = .of_node_get+0x20/0x3c
[C00000001F7837D0] [C00000001F783870] 0xc00000001f783870 (unreliable)
[C00000001F783850] [C000000000020F1C] .of_get_parent+0x38/0x64
[C00000001F7838E0] [C00000000001ACE4] .of_irq_map_raw+0x100/0x4cc
[C00000001F7839E0] [C00000000001B190] .of_irq_map_one+0xe0/0x11c
[C00000001F783A90] [C00000000001BFB4] .of_irq_map_pci+0x74/0x1b8
[C00000001F783B40] [C0000000000271EC] .pci_read_irq_line+0x20/0x100
[C00000001F783BF0] [C00000000002741C] .do_bus_setup+0x94/0x108
[C00000001F783C80] [C000000000027538] .pcibios_fixup_bus+0xa8/0x11c
[C00000001F783D00] [C000000000196620] .pci_scan_child_bus+0x64/0x100
[C00000001F783DA0] [C000000000028388] .scan_phb+0x1a0/0x1d8
[C00000001F783E40] [C00000000045A190] .pcibios_init+0x4c/0x18c
[C00000001F783EC0] [C0000000000093AC] .init+0x1bc/0x394
[C00000001F783F90] [C000000000023364] .kernel_thread+0x4c/0x68
PCI: Transparent bridge - 0000:00:01.0

--
dwmw2

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Next message: Christoph Hellwig: "Re: [PATCH] Open Firmware device tree virtual filesystem"
Previous message: Fengguang Wu: "[BUG 2.6.20-rc2-mm1] init segfaults when CONFIG_PROFILE_LIKELY=y"
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