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SubjectRe: [PATCH] kobject: fix double kobject_put in kobject_unregister()
On Wed, 10 Nov 2004 15:04:01 -0800 Keshavamurthy Anil S wrote:
> On Wed, Nov 10, 2004 at 02:54:21PM -0800, Greg KH wrote:
> > On Wed, Nov 10, 2004 at 02:19:23PM -0800, Keshavamurthy Anil S wrote:
> > > Hi Greg,
> > >
> > > This patch fixes the problem where in kobject resources were getting
> > > freed when those kobject were still in use due to double kobject_put()
> > > getting called in the kobject_unregister() code path.
> > >
> > > With out this patch kobject_unregister() will have some serious side effects.
> > >
> > > Please apply.
> > >
> > > signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
> > >
> > >
> > > linux-2.6.10-rc1-mm4-askeshav/lib/kobject.c | 3 ++-
> > > 1 files changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff -puN lib/kobject.c~kobject_unregister_fix lib/kobject.c
> > > --- linux-2.6.10-rc1-mm4/lib/kobject.c~kobject_unregister_fix 2004-11-10 13:43:42.243877455 -0800
> > > +++ linux-2.6.10-rc1-mm4-askeshav/lib/kobject.c 2004-11-10 13:46:30.788797265 -0800
> > > @@ -301,6 +301,8 @@ void kobject_del(struct kobject * kobj)
> > > {
> > > kobject_hotplug(kobj, KOBJ_REMOVE);
> > > sysfs_remove_dir(kobj);
> > > +
> > > + /* unlink does kobject_put() for us */
> > > unlink(kobj);
> > > }
> > >
> > > @@ -313,7 +315,6 @@ void kobject_unregister(struct kobject *
> > > {
> > > pr_debug("kobject %s: unregistering\n",kobject_name(kobj));
> > > kobject_del(kobj);
> > > - kobject_put(kobj);
> > > }
> >
> > No, this is wrong. Count the add and put in the sequence of:
> > kobject_register()
> > kobject_unregister()
> >
> > they are balanced.
> >
> > You mention you are seeing problems. Have a trace? Example code?
>
> Here is the call trace when I tried to do kobject_unregiser()
> Call Trace:
> [<a000000100016de0>] show_stack+0x80/0xa0
> sp=e00000000e3cf730 bsp=e00000000e3c9230
> [<a000000100017640>] show_regs+0x840/0x880
> sp=e00000000e3cf900 bsp=e00000000e3c91c8
> [<a000000100023f10>] die+0x150/0x1c0
> sp=e00000000e3cf910 bsp=e00000000e3c9188
> [<a000000100023fc0>] die_if_kernel+0x40/0x60
> sp=e00000000e3cf910 bsp=e00000000e3c9158
> [<a0000001000240f0>] ia64_fault+0x110/0x1060
> sp=e00000000e3cf910 bsp=e00000000e3c9100
> [<a00000010000dae0>] ia64_leave_kernel+0x0/0x260
> sp=e00000000e3cfb20 bsp=e00000000e3c9100
> [<a0000001002743e0>] strlen+0x20/0x140
> sp=e00000000e3cfcf0 bsp=e00000000e3c90a8
> [<a00000010026a270>] kobject_get_path+0x150/0x1e0
> sp=e00000000e3cfcf0 bsp=e00000000e3c9068
> [<a00000010026a770>] kobject_hotplug+0x350/0x6e0
> sp=e00000000e3cfcf0 bsp=e00000000e3c9008
> [<a0000001002695b0>] kobject_del+0x30/0x80
> sp=e00000000e3cfd10 bsp=e00000000e3c8fe0
> [<a000000100269620>] kobject_unregister+0x20/0x60
> sp=e00000000e3cfd10 bsp=e00000000e3c8fc0
> [<a000000100302420>] acpi_device_unregister+0x320/0x340
> sp=e00000000e3cfd10 bsp=e00000000e3c8fa0
> [<a000000100302b70>] acpi_bus_remove+0x2f0/0x340
> sp=e00000000e3cfd10 bsp=e00000000e3c8f68
> [<a000000100302ec0>] acpi_bus_trim+0x300/0x440
> sp=e00000000e3cfd30 bsp=e00000000e3c8f18
> [<a000000100303110>] acpi_eject_store+0x110/0x240
> sp=e00000000e3cfde0 bsp=e00000000e3c8ee0
> [<a000000100301fb0>] acpi_device_attr_store+0x70/0xa0
> sp=e00000000e3cfe20 bsp=e00000000e3c8ea8
> [<a0000001001864b0>] sysfs_write_file+0x270/0x300
> sp=e00000000e3cfe20 bsp=e00000000e3c8e58
> [<a0000001001052e0>] vfs_write+0x200/0x2c0
>
> I will try to explain the what is happening here.
>
> I have a sysfs tree like this.
> .../_SB/LSB0
> .../_SB/LSB0/CPU5
> .../_SB/LSB0/MEM1
> .../_SB/LSB0/MEM2
>
> Say LSB0 is kobj1, CPU5 is kobj2, MEM1 is kobj3, MEM2 is kobj4
>
> All I am trying to do is first I will do kobject_unregister(kobj2),then
> kobject_unregister(kobj3), then kobject_unregister(kobj4) and now
> when I try to do kobject_unregister(kobj1) i.e when I am trying to remove
> LSB0 directory, I am seeing the above stack trace.
>
> The patch I posted fixed this problem.
>
> Let me know if you need more data.

I think the cause is an imbalance between acpi_device_register()
and acpi_device_unregister(). acpi_device_register() is supposed
to increment a refcount of a target kobject (kobj1) and also a kobject
(kobj2) that inherited its kset to the kobj1, but it doesn't today. This
is because the kset is not set to kobj1 before calling kboject_init() for
kobj1. On the other hand, acpi_device_unregister() decrements the
refcount of both kobj1 and kobj2. Thus, kobj2 would be released
unexpectedly if kobjects using the kset of kobj2 are released.

kobject_init(&device->kobj);
strlcpy(device->kobj.name,device->pnp.bus_id,KOBJ_NAME_LEN);
if (parent)
device->kobj.parent = &parent->kobj;
device->kobj.ktype = &ktype_acpi_ns;
device->kobj.kset = &acpi_namespace_kset; <-- kset is set here.
kobject_add(&device->kobj);

I am attaching a patch fixing this. I have added acpi-devel in cc
since this might be an ACPI issue. Excuse my cross posting...

Thanks,
Keiichiro Tokunaga


Signed-off-by: Keiichiro Tokunaga <tokunaga.keiich@jp.fujitsu.com>
Status: Tested on 2.6.10-rc1-mm4
---

linux-2.6.10-rc1-mm4-kei-kei/drivers/acpi/scan.c | 3 +--
1 files changed, 1 insertion(+), 2 deletions(-)

diff -puN drivers/acpi/scan.c~fix_acpi_device_register drivers/acpi/scan.c
--- linux-2.6.10-rc1-mm4-kei/drivers/acpi/scan.c~fix_acpi_device_register 2004-11-11 10:11:26.121101371 +0900
+++ linux-2.6.10-rc1-mm4-kei-kei/drivers/acpi/scan.c 2004-11-11 10:11:39.126072074 +0900
@@ -112,13 +112,12 @@ static void acpi_device_register(struct
list_add_tail(&device->wakeup_list,&acpi_wakeup_device_list);
spin_unlock(&acpi_device_lock);

- kobject_init(&device->kobj);
strlcpy(device->kobj.name,device->pnp.bus_id,KOBJ_NAME_LEN);
if (parent)
device->kobj.parent = &parent->kobj;
device->kobj.ktype = &ktype_acpi_ns;
device->kobj.kset = &acpi_namespace_kset;
- kobject_add(&device->kobj);
+ kobject_register(&device->kobj);
create_sysfs_device_files(device);
}

_
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