Re: [linux-usb-devel] [PATCH] back out sysfs reference count change

From: Maneesh Soni
Date: Wed Mar 31 2004 - 04:23:07 EST

On Tue, Mar 30, 2004 at 06:19:15PM -0800, Andrew Morton wrote:
> But it looks like that's all in a faraway perfect world, and Greg is going
> to fix stuff up somehow ;)

For convenience I will explain the race here..

cpu 0 cpu 1
kobject_unregister() sysfs_open_file()
kobject_del() check_perm()
sysfs_remove_dir() :
(dentry remains alive due to ref. taken :
on the way to sysfs_open_file) :
kobject_put() :
kobject_cleanup() kobject_get(->d_fsdata)

cpu 1 could end up referring to a freed kobject through dentry->d_fsdata or
starts spitting Badness in kobject_get at lib/kobject.c:429. For triggering
this race try running these two loops simultaneously on SMP

# while true; do insmod drivers/net/dummy.ko; rmmod dummy; done
# while true; do find /sys/class/net | xargs cat; done

Probably it can be solved by making sure that when sysfs file is
opened/read/written some _race_ free check is done and fail if kobject if gone.


Maneesh Soni
Linux Technology Center,
IBM Software Lab, Bangalore, India
email: maneesh@xxxxxxxxxx
Phone: 91-80-25044999 Fax: 91-80-25268553
T/L : 9243696
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at